fix some terms
This commit is contained in:
stanzhai
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# 特性
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特性提供了关于声明和类型的更多信息。在Swift中有两类特性，用于修饰声明的以及用于修饰类型的。例如，`required`特性，当应用于一个类的指定或便利初始化器声明时，表明它的每个子类都必须实现那个初始化器。再比如`noreturn`特性，当应用于函数或方法类型时，表明该函数或方法不会返回到它的调用者。
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通过以下方式指定一个特性：符号`@`后面跟特性名，如果包含参数，则把参数带上：
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```
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@attribute name
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@attribute name(attribute arguments)
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```
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有些声明特性通过接收参数来指定特性的更多信息以及它是如何修饰一个特定的声明的。这些特性的参数写在小括号内，它们的格式由它们所属的特性来定义。
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## 声明特性
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声明特性只能应用于声明。然而，你也可以将`noreturn`特性应用于函数或方法类型。
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`assignment`
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该特性用于修饰重载了复合赋值运算符的函数。重载了复合赋值运算符的函数必需将它们的初始输入参数标记为`inout`。如何使用`assignment`特性的一个例子，请见：[复合赋值运算符]()。
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`class_protocol`
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该特性用于修饰一个协议表明该协议只能被类类型采用[待改：adopted]。
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如果你用`objc`特性修饰一个协议，`class_protocol`特性就会隐式地应用到该协议，因此无需显式地用`class_protocol`特性标记该协议。
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`exported`
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该特性用于修饰导入声明，以此来导出已导入的模块，子模块，或当前模块的声明。如果另一个模块导入了当前模块，那么那个模块可以访问当前模块的导出项。
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`final`
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该特性用于修饰一个类或类中的属性，方法，以及下标成员。如果用它修饰一个类，那么这个类则不能被继承。如果用它修饰类中的属性，方法或下标，则表示在子类中，它们不能被重写。
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`lazy`
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该特性用于修饰类或结构体中的存储型变量属性，表示该属性的初始值最多只被计算和存储一次，且发生在第一次访问它时。如何使用`lazy`特性的一个例子，请见：[惰性存储型属性]()。
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`noreturn`
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该特性用于修饰函数或方法声明，表明该函数或方法的对应类型，`T`，是`@noreturn T`。你可以用这个特性修饰函数或方法的类型，这样一来，函数或方法就不会返回到它的调用者中去。
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对于一个没有用`noreturn`特性标记的函数或方法，你可以将它重写(override)为用该特性标记的。相反，对于一个已经用`noreturn`特性标记的函数或方法，你则不可以将它重写为没使用该特性标记的。相同的规则试用于当你在一个comforming类型中实现一个协议方法时。
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`NSCopying`
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该特性用于修饰一个类的存储型变量属性。该特性将使属性的setter与属性值的一个副本合成，由`copyWithZone`方法返回，而不是属性本身的值。该属性的类型必需遵循`NSCopying`协议。
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`NSCopying`特性的行为与Objective-C中的`copy`特性相似。
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`NSManaged`
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该特性用于修饰`NSManagedObject`子类中的存储型变量属性，表明属性的存储和实现由Core Data在运行时基于相关实体描述动态提供。
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`objc`
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该特性用于修饰任意可以在Objective-C中表示的声明，比如，非嵌套类，协议，类和协议中的属性和方法（包含getter和setter），初始化器，析构器，以下下标。`objc`特性告诉编译器该声明可以在Objective-C代码中使用。
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如果你将`objc`特性应用于一个类或协议，它也会隐式地应用于那个类或协议的成员。对于标记了`objc`特性的类，编译器会隐式地为它的子类添加`objc`特性。标记了`objc`特性的协议不能继承自没有标记`objc`的协议。
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`objc`特性有一个可选的参数，由标记符组成。当你想把`objc`所修饰的实体以一个不同的名字暴露给Objective-C，你就可以使用这个特性参数。你可以使用这个参数来命名类，协议，方法，getters，setters，以及初始化器。下面的例子把`ExampleClass`中`enabled`属性的getter暴露给Objective-C，名字是`isEnabled`，而不是它原来的属性名。
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```
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@objc
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class ExampleClass {
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var enabled: Bool {
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@objc(isEnabled) get {
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// Return the appropriate value
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}
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}
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}
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```
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`optional`
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用该特性修饰协议的属性，方法或下标成员，表示实现这些成员并不需要一致性类型（conforming type）。
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你只能用`optional`特性修饰那些标记了`objc`特性的协议。因此，只有类类型可以adopt和comform to那些包含可选成员需求的协议。更多关于如何使用`optional`特性以及如何访问可选协议成员的指导，例如，当你不确定一个conforming类型是否实现了它们，请见：[可选协议需求]()。
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`required`
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用该特性修饰一个类的指定或便利初始化器，表示该类的所有子类都必需实现该初始化器。
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加了该特性的指定初始化器必需显式地实现，而便利初始化器既可显式地实现，也可以在子类实现了超类所有指定初始化器后继承而来（或者当子类使用便利初始化器重写了指定初始化器）。
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### Interface Builder使用的声明特性
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Interface Builder特性是Interface Builder用来与Xcode同步的声明特性。Swift提供了以下的Interface Builder特性：`IBAction`，`IBDesignable`，`IBInspectable`，以及`IBOutlet`。这些特性与Objective-C中对应的特性在概念上是相同的。
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`IBOutlet`和`IBInspectable`用于修饰一个类的属性声明；`IBAction`特性用于修饰一个类的方法声明；`IBDesignable`用于修饰类的声明。
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## 类型特性
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类型特性只能用于修饰类型。然而，你也可以用`noreturn`特性去修饰函数或方法声明。
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`auto_closure`
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这个特性通过自动地将表达式封闭到一个无参数闭包中来延迟表达式的求值。使用该特性修饰无参的函数或方法类型，返回表达式的类型。一个如何使用`auto_closure`特性的例子，见[函数类型]()
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`noreturn`
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该特性用于修饰函数或方法的类型，表明该函数或方法不会返回到它的调用者中去。你也可以用它标记函数或方法的声明，表示函数或方法的相应类型，`T`，是`@noreturn T`。
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> 特性的语法
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> attribute -> @ [attribute-name]() [attribute-argument-clause]()opt
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> attribute-name -> [identifier]()
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> attribute-argument-clause -> ( [balanced-tokens]()opt )
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> attributes -> [attribute]() [attributes]()opt
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> balanced-tokens -> [balanced-token]() [balanced-tokens]()opt
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> balanced-token -> ( [balanced-tokens]()opt )
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> balanced-token -> [ [balanced-tokens]()opt ]
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> balanced-token -> { [balanced-tokens]()opt }
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> balanced-token -> 任意标识符，关键字，字面量，或运算符
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> balanced-token -> 任意标点符号，除了(, ), [, ], {, 或 }
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@ -1,57 +1,738 @@
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# 语法总结 (Summary of the Grammar)
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## 语句
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`结构已搞定，内容已填充，翻译仍在进行中...`
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> 语句
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*statement* → [*expression*]() ; opt
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*statement* → [*declaration*]() ; opt
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*statement* → [*loop-statement*]() ; opt
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*statement* → [*branch-statement*]() ; opt
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*statement* → [*labeled-statement*]()
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*statement* → [*control-transfer-statement*]() ; opt
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*statements* → [*statement statement*]() opt
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## 语句 (Statements)
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<p></p>
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> 循环语句
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> *loop-statement* → [*for-statement*]()
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> *loop-statement* → [*for-in-statement*]()
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> *loop-statement* → [*while-statement*]()
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> *loop-statement* → [*do-while-statement*]()
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> 语句 (Grammar of a statement)
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> *statement* → [*expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression) **;** _opt_
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> *statement* → [*declaration*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/declaration) **;** _opt_
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> *statement* → [*loop-statement*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/loop-statement) **;** _opt_
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> *statement* → [*branch-statement*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/branch-statement) **;** _opt_
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> *statement* → [*labeled-statement*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/labeled-statement)
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> *statement* → [*control-transfer-statement*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/control-transfer-statement) **;** _opt_
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> *statements* → [*statement*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/statement) [*statements*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/statements) _opt_
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<p></p>
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> for 循环
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> *for-statement* → **for** [*for-init*]() opt ; [*expression*]() opt ; [*expression*]() opt [*code-block*]()
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> *for-statement* → **for** ( [*for-init*]() opt ; [*expression*]() opt ; [*expression*]() opt ) [*code-block*]()
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> *for-init* → [*variable-declaration*]() | [*expression-list*]()
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> 循环语句 (Grammar of a loop statement)
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> *loop-statement* → [*for-statement*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/for-statement)
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> *loop-statement* → [*for-in-statement*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/for-in-statement)
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> *loop-statement* → [*while-statement*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/wheetatype类型ile-statement)
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> *loop-statement* → [*do-while-statement*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/do-while-statement)
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<p></p>
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> for-in 循环
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> *for-in-statement* → **for** [*pattern*]() **in** [*expression*]() [*code-block*]()
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> For 循环 (Grammar of a for statement)
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> *for-statement* → **for** [*for-init*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/for-init) _opt_ **;** [*expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression) _opt_ **;** [*expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression) _opt_ [*code-block*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/code-block)
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> *for-statement* → **for** **(** [*for-init*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/for-init) _opt_ **;** [*expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression) _opt_ **;** [*expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression) _opt_ **)** [*code-block*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/code-block)
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> *for-init* → [*variable-declaration*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/variable-declaration) | [*expression-list*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression-list)
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<p></p>
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> while 循环
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> *while-statement* → **while** [*while-condition*]() [*code-block*]()
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> *while-condition* → [*expression*]() | [*declaration*]()
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> For-In 循环 (Grammar of a for-in statement)
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> *for-in-statement* → **for** [*pattern*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Patterns.html#//apple_ref/swift/grammar/pattern) **in** [*expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression) [*code-block*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/code-block)
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<p></p>
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> do-while 循环
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> *do-while-statement* → **do** [*code-block*]() **while** [*while-condition*]()
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> While 循环 (Grammar of a while statement)
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> *while-statement* → **while** [*while-condition*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/while-condition) [*code-block*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/code-block)
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> *while-condition* → [*expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression) | [*declaration*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/declaration)
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<p></p>
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> 判断语句(Branch Statement)
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> *branch-statement* → [*if-statement*]()
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> *branch-statement* → [*switch-statement*]()
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> Do-While 循环 (Grammar of a do-while statement)
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> *do-while-statement* → **do** [*code-block*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/code-block) **while** [*while-condition*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/while-condition)
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<p></p>
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> if 语句
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> *if-statement* → **if** [*if-condition*]() [*code-block*]() [*else-clause*]() opt
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> *if-condition* → [*expression*]() | [*declaration*]()
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> *else-clause* → **else** [*code-block*]() | **else** [*if-statement*]()
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> 分支语句 (Grammar of a branch statement)
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> *branch-statement* → [*if-statement*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/if-statement)
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> *branch-statement* → [*switch-statement*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/switch-statement)
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<p></p>
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> If 语句 (Grammar of an if statement)
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> *if-statement* → **if** [*if-condition*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/if-condition) [*code-block*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/code-block) [*else-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/else-clause) _opt_
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> *if-condition* → [*expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression) | [*declaration*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/declaration)
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> *else-clause* → **else** [*code-block*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/code-block) | **else** [*if-statement*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/if-statement)
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<p></p>
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> Switch 语句 (Grammar of a switch statement)
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> *switch-statement* → **switch** [*expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression) **{** [*switch-cases*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/switch-cases) _opt_ **}**
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> *switch-cases* → [*switch-case*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/switch-case) [*switch-cases*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/switch-cases) _opt_
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> *switch-case* → [*case-label*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/case-label) [*statements*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/statements) | [*default-label*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/default-label) [*statements*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/statements)
|
||||
> *switch-case* → [*case-label*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/case-label) **;** | [*default-label*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/default-label) **;**
|
||||
> *case-label* → **case** [*case-item-list*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/case-item-list) **:**
|
||||
> *case-item-list* → [*pattern*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Patterns.html#//apple_ref/swift/grammar/pattern) [*guard-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/guard-clause) _opt_ | [*pattern*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Patterns.html#//apple_ref/swift/grammar/pattern) [*guard-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/guard-clause) _opt_ **,** [*case-item-list*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/case-item-list)
|
||||
> *default-label* → **default** **:**
|
||||
> *guard-clause* → **where** [*guard-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/guard-expression)
|
||||
> *guard-expression* → [*expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 带标签的语句 (Grammar of a labeled statement)
|
||||
> *labeled-statement* → [*statement-label*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/statement-label) [*loop-statement*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/loop-statement) | [*statement-label*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/statement-label) [*switch-statement*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/switch-statement)
|
||||
> *statement-label* → [*label-name*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/label-name) **:**
|
||||
> *label-name* → [*identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 控制传递语句 (Grammar of a control transfer statement)
|
||||
> *control-transfer-statement* → [*break-statement*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/break-statement)
|
||||
> *control-transfer-statement* → [*continue-statement*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/continue-statement)
|
||||
> *control-transfer-statement* → [*fallthrough-statement*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/fallthrough-statement)
|
||||
> *control-transfer-statement* → [*return-statement*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/return-statement)
|
||||
|
||||
<p></p>
|
||||
|
||||
> Break 语句 (Grammar of a break statement)
|
||||
> *break-statement* → **break** [*label-name*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/label-name) _opt_
|
||||
|
||||
<p></p>
|
||||
|
||||
> Continue 语句 (Grammar of a continue statement)
|
||||
> *continue-statement* → **continue** [*label-name*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/label-name) _opt_
|
||||
|
||||
<p></p>
|
||||
|
||||
> Fallthrough 语句 (Grammar of a fallthrough statement)
|
||||
> *fallthrough-statement* → **fallthrough**
|
||||
|
||||
<p></p>
|
||||
|
||||
> Return 语句 (Grammar of a return statement)
|
||||
> *return-statement* → **return** [*expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression) _opt_
|
||||
|
||||
## 泛型参数 (Generic Parameters and Arguments)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 泛型形参子句 (Grammar of a generic parameter clause)
|
||||
> *generic-parameter-clause* → **<** [*generic-parameter-list*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/GenericParametersAndArguments.html#//apple_ref/swift/grammar/generic-parameter-list) [*requirement-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/GenericParametersAndArguments.html#//apple_ref/swift/grammar/requirement-clause) _opt_ **>**
|
||||
> *generic-parameter-list* → [*generic-parameter*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/GenericParametersAndArguments.html#//apple_ref/swift/grammar/generic-parameter) | [*generic-parameter*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/GenericParametersAndArguments.html#//apple_ref/swift/grammar/generic-parameter) **,** [*generic-parameter-list*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/GenericParametersAndArguments.html#//apple_ref/swift/grammar/generic-parameter-list)
|
||||
> *generic-parameter* → [*type-name*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type-name)
|
||||
> *generic-parameter* → [*type-name*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type-name) **:** [*type-identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type-identifier)
|
||||
> *generic-parameter* → [*type-name*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type-name) **:** [*protocol-composition-type*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/protocol-composition-type)
|
||||
> *requirement-clause* → **where** [*requirement-list*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/GenericParametersAndArguments.html#//apple_ref/swift/grammar/requirement-list)
|
||||
> *requirement-list* → [*requirement*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/GenericParametersAndArguments.html#//apple_ref/swift/grammar/requirement) | [*requirement*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/GenericParametersAndArguments.html#//apple_ref/swift/grammar/requirement) **,** [*requirement-list*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/GenericParametersAndArguments.html#//apple_ref/swift/grammar/requirement-list)
|
||||
> *requirement* → [*conformance-requirement*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/GenericParametersAndArguments.html#//apple_ref/swift/grammar/conformance-requirement) | [*same-type-requirement*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/GenericParametersAndArguments.html#//apple_ref/swift/grammar/same-type-requirement)
|
||||
> *conformance-requirement* → [*type-identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type-identifier) **:** [*type-identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type-identifier)
|
||||
> *conformance-requirement* → [*type-identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type-identifier) **:** [*protocol-composition-type*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/protocol-composition-type)
|
||||
> *same-type-requirement* → [*type-identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type-identifier) **==** [*type-identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type-identifier)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 泛型参数子句 (Grammar of a generic argument clause)
|
||||
> *generic-argument-clause* → **<** [*generic-argument-list*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/GenericParametersAndArguments.html#//apple_ref/swift/grammar/generic-argument-list) **>**
|
||||
> *generic-argument-list* → [*generic-argument*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/GenericParametersAndArguments.html#//apple_ref/swift/grammar/generic-argument) | [*generic-argument*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/GenericParametersAndArguments.html#//apple_ref/swift/grammar/generic-argument) **,** [*generic-argument-list*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/GenericParametersAndArguments.html#//apple_ref/swift/grammar/generic-argument-list)
|
||||
> *generic-argument* → [*type*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type)
|
||||
|
||||
## 声明 (Declarations)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 声明语法 (Grammar of a declaration)
|
||||
> *declaration* → [*import-declaration*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/import-declaration)
|
||||
> *declaration* → [*constant-declaration*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/constant-declaration)
|
||||
> *declaration* → [*variable-declaration*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/variable-declaration)
|
||||
> *declaration* → [*typealias-declaration*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/typealias-declaration)
|
||||
> *declaration* → [*function-declaration*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/function-declaration)
|
||||
> *declaration* → [*enum-declaration*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/enum-declaration)
|
||||
> *declaration* → [*struct-declaration*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/struct-declaration)
|
||||
> *declaration* → [*class-declaration*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/class-declaration)
|
||||
> *declaration* → [*protocol-declaration*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/protocol-declaration)
|
||||
> *declaration* → [*initializer-declaration*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/initializer-declaration)
|
||||
> *declaration* → [*deinitializer-declaration*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/deinitializer-declaration)
|
||||
> *declaration* → [*extension-declaration*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/extension-declaration)
|
||||
> *declaration* → [*subscript-declaration*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/subscript-declaration)
|
||||
> *declaration* → [*operator-declaration*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/operator-declaration)
|
||||
> *declarations* → [*declaration*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/declaration) [*declarations*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/declarations) _opt_
|
||||
> *declaration-specifiers* → [*declaration-specifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/declaration-specifier) [*declaration-specifiers*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/declaration-specifiers) _opt_
|
||||
> *declaration-specifier* → **class** | **mutating** | **nonmutating** | **override** | **static** | **unowned** | **unowned(safe)** | **unowned(unsafe)** | **weak**
|
||||
|
||||
<p></p>
|
||||
|
||||
> (Grammar of a top-level declaration)
|
||||
> *top-level-declaration* → [*statements*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/statements) _opt_
|
||||
|
||||
<p></p>
|
||||
|
||||
> 代码块 (Grammar of a code block)
|
||||
> *code-block* → **{** [*statements*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/statements) _opt_ **}**
|
||||
|
||||
<p></p>
|
||||
|
||||
> (Grammar of an import declaration)
|
||||
> *import-declaration* → [*attributes*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Attributes.html#//apple_ref/swift/grammar/attributes) _opt_ **import** [*import-kind*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/import-kind) _opt_ [*import-path*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/import-path)
|
||||
> *import-kind* → **typealias** | **struct** | **class** | **enum** | **protocol** | **var** | **func**
|
||||
> *import-path* → [*import-path-identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/import-path-identifier) | [*import-path-identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/import-path-identifier) **.** [*import-path*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/import-path)
|
||||
> *import-path-identifier* → [*identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier) | [*operator*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/operator)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 常数声明 (Grammar of a constant declaration)
|
||||
> *constant-declaration* → [*attributes*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Attributes.html#//apple_ref/swift/grammar/attributes) _opt_ [*declaration-specifiers*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/declaration-specifiers) _opt_ **let** [*pattern-initializer-list*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/pattern-initializer-list)
|
||||
> *pattern-initializer-list* → [*pattern-initializer*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/pattern-initializer) | [*pattern-initializer*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/pattern-initializer) **,** [*pattern-initializer-list*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/pattern-initializer-list)
|
||||
> *pattern-initializer* → [*pattern*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Patterns.html#//apple_ref/swift/grammar/pattern) [*initializer*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/initializer) _opt_
|
||||
> *initializer* → **=** [*expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 变量声明 (Grammar of a variable declaration)
|
||||
> *variable-declaration* → [*variable-declaration-head*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/variable-declaration-head) [*pattern-initializer-list*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/pattern-initializer-list)
|
||||
> *variable-declaration* → [*variable-declaration-head*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/variable-declaration-head) [*variable-name*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/variable-name) [*type-annotation*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type-annotation) [*code-block*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/code-block)
|
||||
> *variable-declaration* → [*variable-declaration-head*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/variable-declaration-head) [*variable-name*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/variable-name) [*type-annotation*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type-annotation) [*getter-setter-block*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/getter-setter-block)
|
||||
> *variable-declaration* → [*variable-declaration-head*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/variable-declaration-head) [*variable-name*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/variable-name) [*type-annotation*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type-annotation) [*getter-setter-keyword-block*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/getter-setter-keyword-block)
|
||||
> *variable-declaration* → [*variable-declaration-head*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/variable-declaration-head) [*variable-name*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/variable-name) [*type-annotation*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type-annotation) [*initializer*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/initializer) _opt_ [*willSet-didSet-block*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/willSet-didSet-block)
|
||||
> *variable-declaration-head* → [*attributes*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Attributes.html#//apple_ref/swift/grammar/attributes) _opt_ [*declaration-specifiers*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/declaration-specifiers) _opt_ **var**
|
||||
> *variable-name* → [*identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier)
|
||||
> *getter-setter-block* → **{** [*getter-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/getter-clause) [*setter-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/setter-clause) _opt_ **}**
|
||||
> *getter-setter-block* → **{** [*setter-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/setter-clause) [*getter-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/getter-clause) **}**
|
||||
> *getter-clause* → [*attributes*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Attributes.html#//apple_ref/swift/grammar/attributes) _opt_ **get** [*code-block*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/code-block)
|
||||
> *setter-clause* → [*attributes*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Attributes.html#//apple_ref/swift/grammar/attributes) _opt_ **set** [*setter-name*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/setter-name) _opt_ [*code-block*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/code-block)
|
||||
> *setter-name* → **(** [*identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier) **)**
|
||||
> *getter-setter-keyword-block* → **{** [*getter-keyword-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/getter-keyword-clause) [*setter-keyword-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/setter-keyword-clause) _opt_ **}**
|
||||
> *getter-setter-keyword-block* → **{** [*setter-keyword-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/setter-keyword-clause) [*getter-keyword-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/getter-keyword-clause) **}**
|
||||
> *getter-keyword-clause* → [*attributes*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Attributes.html#//apple_ref/swift/grammar/attributes) _opt_ **get**
|
||||
> *setter-keyword-clause* → [*attributes*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Attributes.html#//apple_ref/swift/grammar/attributes) _opt_ **set**
|
||||
> *willSet-didSet-block* → **{** [*willSet-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/willSet-clause) [*didSet-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/didSet-clause) _opt_ **}**
|
||||
> *willSet-didSet-block* → **{** [*didSet-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/didSet-clause) [*willSet-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/willSet-clause) **}**
|
||||
> *willSet-clause* → [*attributes*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Attributes.html#//apple_ref/swift/grammar/attributes) _opt_ **willSet** [*setter-name*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/setter-name) _opt_ [*code-block*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/code-block)
|
||||
> *didSet-clause* → [*attributes*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Attributes.html#//apple_ref/swift/grammar/attributes) _opt_ **didSet** [*setter-name*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/setter-name) _opt_ [*code-block*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/code-block)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 类型别名声明 (Grammar of a type alias declaration)
|
||||
> *typealias-declaration* → [*typealias-head*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/typealias-head) [*typealias-assignment*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/typealias-assignment)
|
||||
> *typealias-head* → **typealias** [*typealias-name*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/typealias-name)
|
||||
> *typealias-name* → [*identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier)
|
||||
> *typealias-assignment* → **=** [*type*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 函数声明 (Grammar of a function declaration)
|
||||
> *function-declaration* → [*function-head*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/function-head) [*function-name*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/function-name) [*generic-parameter-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/GenericParametersAndArguments.html#//apple_ref/swift/grammar/generic-parameter-clause) _opt_ [*function-signature*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/function-signature) [*function-body*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/function-body)
|
||||
> *function-head* → [*attributes*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Attributes.html#//apple_ref/swift/grammar/attributes) _opt_ [*declaration-specifiers*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/declaration-specifiers) _opt_ **func**
|
||||
> *function-name* → [*identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier) | [*operator*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/operator)
|
||||
> *function-signature* → [*parameter-clauses*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/parameter-clauses) [*function-result*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/function-result) _opt_
|
||||
> *function-result* → **->** [*attributes*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Attributes.html#//apple_ref/swift/grammar/attributes) _opt_ [*type*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type)
|
||||
> *function-body* → [*code-block*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/code-block)
|
||||
> *parameter-clauses* → [*parameter-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/parameter-clause) [*parameter-clauses*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/parameter-clauses) _opt_
|
||||
> *parameter-clause* → **(** **)** | **(** [*parameter-list*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/parameter-list) **...** _opt_ **)**
|
||||
> *parameter-list* → [*parameter*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/parameter) | [*parameter*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/parameter) **,** [*parameter-list*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/parameter-list)
|
||||
> *parameter* → **inout** _opt_ **let** _opt_ **#** _opt_ [*parameter-name*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/parameter-name) [*local-parameter-name*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/local-parameter-name) _opt_ [*type-annotation*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type-annotation) [*default-argument-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/default-argument-clause) _opt_
|
||||
> *parameter* → **inout** _opt_ **var** **#** _opt_ [*parameter-name*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/parameter-name) [*local-parameter-name*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/local-parameter-name) _opt_ [*type-annotation*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type-annotation) [*default-argument-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/default-argument-clause) _opt_
|
||||
> *parameter* → [*attributes*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Attributes.html#//apple_ref/swift/grammar/attributes) _opt_ [*type*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type)
|
||||
> *parameter-name* → [*identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier) | **_**
|
||||
> *local-parameter-name* → [*identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier) | **_**
|
||||
> *default-argument-clause* → **=** [*expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 枚举声明 (Grammar of an enumeration declaration)
|
||||
> *enum-declaration* → [*attributes*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Attributes.html#//apple_ref/swift/grammar/attributes) _opt_ [*union-style-enum*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/union-style-enum) | [*attributes*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Attributes.html#//apple_ref/swift/grammar/attributes) _opt_ [*raw-value-style-enum*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/raw-value-style-enum)
|
||||
> *union-style-enum* → [*enum-name*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/enum-name) [*generic-parameter-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/GenericParametersAndArguments.html#//apple_ref/swift/grammar/generic-parameter-clause) _opt_ **{** [*union-style-enum-members*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/union-style-enum-members) _opt_ **}**
|
||||
> *union-style-enum-members* → [*union-style-enum-member*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/union-style-enum-member) [*union-style-enum-members*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/union-style-enum-members) _opt_
|
||||
> *union-style-enum-member* → [*declaration*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/declaration) | [*union-style-enum-case-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/union-style-enum-case-clause)
|
||||
> *union-style-enum-case-clause* → [*attributes*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Attributes.html#//apple_ref/swift/grammar/attributes) _opt_ **case** [*union-style-enum-case-list*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/union-style-enum-case-list)
|
||||
> *union-style-enum-case-list* → [*union-style-enum-case*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/union-style-enum-case) | [*union-style-enum-case*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/union-style-enum-case) **,** [*union-style-enum-case-list*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/union-style-enum-case-list)
|
||||
> *union-style-enum-case* → [*enum-case-name*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/enum-case-name) [*tuple-type*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/tuple-type) _opt_
|
||||
> *enum-name* → [*identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier)
|
||||
> *enum-case-name* → [*identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier)
|
||||
> *raw-value-style-enum* → [*enum-name*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/enum-name) [*generic-parameter-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/GenericParametersAndArguments.html#//apple_ref/swift/grammar/generic-parameter-clause) _opt_ **:** [*type-identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type-identifier) **{** [*raw-value-style-enum-members*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/raw-value-style-enum-members) _opt_ **}**
|
||||
> *raw-value-style-enum-members* → [*raw-value-style-enum-member*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/raw-value-style-enum-member) [*raw-value-style-enum-members*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/raw-value-style-enum-members) _opt_
|
||||
> *raw-value-style-enum-member* → [*declaration*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/declaration) | [*raw-value-style-enum-case-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/raw-value-style-enum-case-clause)
|
||||
> *raw-value-style-enum-case-clause* → [*attributes*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Attributes.html#//apple_ref/swift/grammar/attributes) _opt_ **case** [*raw-value-style-enum-case-list*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/raw-value-style-enum-case-list)
|
||||
> *raw-value-style-enum-case-list* → [*raw-value-style-enum-case*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/raw-value-style-enum-case) | [*raw-value-style-enum-case*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/raw-value-style-enum-case) **,** [*raw-value-style-enum-case-list*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/raw-value-style-enum-case-list)
|
||||
> *raw-value-style-enum-case* → [*enum-case-name*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/enum-case-name) [*raw-value-assignment*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/raw-value-assignment) _opt_
|
||||
> *raw-value-assignment* → **=** [*literal*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/literal)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 结构体声明 (Grammar of a structure declaration)
|
||||
> *struct-declaration* → [*attributes*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Attributes.html#//apple_ref/swift/grammar/attributes) _opt_ **struct** [*struct-name*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/struct-name) [*generic-parameter-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/GenericParametersAndArguments.html#//apple_ref/swift/grammar/generic-parameter-clause) _opt_ [*type-inheritance-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type-inheritance-clause) _opt_ [*struct-body*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/struct-body)
|
||||
> *struct-name* → [*identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier)
|
||||
> *struct-body* → **{** [*declarations*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/declarations) _opt_ **}**
|
||||
|
||||
<p></p>
|
||||
|
||||
> 类声明 (Grammar of a class declaration)
|
||||
> *class-declaration* → [*attributes*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Attributes.html#//apple_ref/swift/grammar/attributes) _opt_ **class** [*class-name*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/class-name) [*generic-parameter-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/GenericParametersAndArguments.html#//apple_ref/swift/grammar/generic-parameter-clause) _opt_ [*type-inheritance-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type-inheritance-clause) _opt_ [*class-body*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/class-body)
|
||||
> *class-name* → [*identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier)
|
||||
> *class-body* → **{** [*declarations*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/declarations) _opt_ **}**
|
||||
|
||||
<p></p>
|
||||
|
||||
> 协议声明 (Grammar of a protocol declaration)
|
||||
> *protocol-declaration* → [*attributes*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Attributes.html#//apple_ref/swift/grammar/attributes) _opt_ **protocol** [*protocol-name*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/protocol-name) [*type-inheritance-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type-inheritance-clause) _opt_ [*protocol-body*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/protocol-body)
|
||||
> *protocol-name* → [*identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier)
|
||||
> *protocol-body* → **{** [*protocol-member-declarations*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/protocol-member-declarations) _opt_ **}**
|
||||
> *protocol-member-declaration* → [*protocol-property-declaration*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/protocol-property-declaration)
|
||||
> *protocol-member-declaration* → [*protocol-method-declaration*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/protocol-method-declaration)
|
||||
> *protocol-member-declaration* → [*protocol-initializer-declaration*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/protocol-initializer-declaration)
|
||||
> *protocol-member-declaration* → [*protocol-subscript-declaration*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/protocol-subscript-declaration)
|
||||
> *protocol-member-declaration* → [*protocol-associated-type-declaration*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/protocol-associated-type-declaration)
|
||||
> *protocol-member-declarations* → [*protocol-member-declaration*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/protocol-member-declaration) [*protocol-member-declarations*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/protocol-member-declarations) _opt_
|
||||
|
||||
<p></p>
|
||||
|
||||
> 协议属性声明 (Grammar of a protocol property declaration)
|
||||
> *protocol-property-declaration* → [*variable-declaration-head*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/variable-declaration-head) [*variable-name*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/variable-name) [*type-annotation*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type-annotation) [*getter-setter-keyword-block*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/getter-setter-keyword-block)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 协议方法声明 (Grammar of a protocol method declaration)
|
||||
> *protocol-method-declaration* → [*function-head*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/function-head) [*function-name*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/function-name) [*generic-parameter-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/GenericParametersAndArguments.html#//apple_ref/swift/grammar/generic-parameter-clause) _opt_ [*function-signature*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/function-signature)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 协议构造函数声明 (Grammar of a protocol initializer declaration)
|
||||
> *protocol-initializer-declaration* → [*initializer-head*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/initializer-head) [*generic-parameter-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/GenericParametersAndArguments.html#//apple_ref/swift/grammar/generic-parameter-clause) _opt_ [*parameter-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/parameter-clause)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 协议附属脚本声明 (Grammar of a protocol subscript declaration)
|
||||
> *protocol-subscript-declaration* → [*subscript-head*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/subscript-head) [*subscript-result*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/subscript-result) [*getter-setter-keyword-block*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/getter-setter-keyword-block)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 协议关联类型声明 (Grammar of a protocol associated type declaration)
|
||||
> *protocol-associated-type-declaration* → [*typealias-head*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/typealias-head) [*type-inheritance-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type-inheritance-clause) _opt_ [*typealias-assignment*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/typealias-assignment) _opt_
|
||||
|
||||
<p></p>
|
||||
|
||||
> 构造函数声明 (Grammar of an initializer declaration)
|
||||
> *initializer-declaration* → [*initializer-head*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/initializer-head) [*generic-parameter-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/GenericParametersAndArguments.html#//apple_ref/swift/grammar/generic-parameter-clause) _opt_ [*parameter-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/parameter-clause) [*initializer-body*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/initializer-body)
|
||||
> *initializer-head* → [*attributes*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Attributes.html#//apple_ref/swift/grammar/attributes) _opt_ **convenience** _opt_ **init**
|
||||
> *initializer-body* → [*code-block*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/code-block)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 析构函数声明 (Grammar of a deinitializer declaration)
|
||||
> *deinitializer-declaration* → [*attributes*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Attributes.html#//apple_ref/swift/grammar/attributes) _opt_ **deinit** [*code-block*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/code-block)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 扩展声明 (Grammar of an extension declaration)
|
||||
> *extension-declaration* → **extension** [*type-identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type-identifier) [*type-inheritance-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type-inheritance-clause) _opt_ [*extension-body*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/extension-body)
|
||||
> *extension-body* → **{** [*declarations*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/declarations) _opt_ **}**
|
||||
|
||||
<p></p>
|
||||
|
||||
> 附属脚本声明 (Grammar of a subscript declaration)
|
||||
> *subscript-declaration* → [*subscript-head*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/subscript-head) [*subscript-result*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/subscript-result) [*code-block*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/code-block)
|
||||
> *subscript-declaration* → [*subscript-head*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/subscript-head) [*subscript-result*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/subscript-result) [*getter-setter-block*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/getter-setter-block)
|
||||
> *subscript-declaration* → [*subscript-head*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/subscript-head) [*subscript-result*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/subscript-result) [*getter-setter-keyword-block*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/getter-setter-keyword-block)
|
||||
> *subscript-head* → [*attributes*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Attributes.html#//apple_ref/swift/grammar/attributes) _opt_ **subscript** [*parameter-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/parameter-clause)
|
||||
> *subscript-result* → **->** [*attributes*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Attributes.html#//apple_ref/swift/grammar/attributes) _opt_ [*type*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 运算符声明 (Grammar of an operator declaration)
|
||||
> *operator-declaration* → [*prefix-operator-declaration*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/prefix-operator-declaration) | [*postfix-operator-declaration*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/postfix-operator-declaration) | [*infix-operator-declaration*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/infix-operator-declaration)
|
||||
> *prefix-operator-declaration* → **operator** **prefix** [*operator*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/operator) **{** **}**
|
||||
> *postfix-operator-declaration* → **operator** **postfix** [*operator*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/operator) **{** **}**
|
||||
> *infix-operator-declaration* → **operator** **infix** [*operator*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/operator) **{** [*infix-operator-attributes*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/infix-operator-attributes) _opt_ **}**
|
||||
> *infix-operator-attributes* → [*precedence-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/precedence-clause) _opt_ [*associativity-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/associativity-clause) _opt_
|
||||
> *precedence-clause* → **precedence** [*precedence-level*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/precedence-level)
|
||||
> *precedence-level* → Digit 0 through 255
|
||||
> *associativity-clause* → **associativity** [*associativity*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/associativity)
|
||||
> *associativity* → **left** | **right** | **none**
|
||||
|
||||
## 模式 (Patterns)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 模式语法 (Grammar of a pattern)
|
||||
> *pattern* → [*wildcard-pattern*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Patterns.html#//apple_ref/swift/grammar/wildcard-pattern) [*type-annotation*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type-annotation) _opt_
|
||||
> *pattern* → [*identifier-pattern*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Patterns.html#//apple_ref/swift/grammar/identifier-pattern) [*type-annotation*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type-annotation) _opt_
|
||||
> *pattern* → [*value-binding-pattern*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Patterns.html#//apple_ref/swift/grammar/value-binding-pattern)
|
||||
> *pattern* → [*tuple-pattern*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Patterns.html#//apple_ref/swift/grammar/tuple-pattern) [*type-annotation*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type-annotation) _opt_
|
||||
> *pattern* → [*enum-case-pattern*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Patterns.html#//apple_ref/swift/grammar/enum-case-pattern)
|
||||
> *pattern* → [*type-casting-pattern*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Patterns.html#//apple_ref/swift/grammar/type-casting-pattern)
|
||||
> *pattern* → [*expression-pattern*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Patterns.html#//apple_ref/swift/grammar/expression-pattern)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 通配符模式 (Grammar of a wildcard pattern)
|
||||
> *wildcard-pattern* → **_**
|
||||
|
||||
<p></p>
|
||||
|
||||
> 标识符模式 (Grammar of an identifier pattern)
|
||||
> *identifier-pattern* → [*identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 值绑定模式 (Grammar of a value-binding pattern)
|
||||
> *value-binding-pattern* → **var** [*pattern*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Patterns.html#//apple_ref/swift/grammar/pattern) | **let** [*pattern*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Patterns.html#//apple_ref/swift/grammar/pattern)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 元组模式 (Grammar of a tuple pattern)
|
||||
> *tuple-pattern* → **(** [*tuple-pattern-element-list*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Patterns.html#//apple_ref/swift/grammar/tuple-pattern-element-list) _opt_ **)**
|
||||
> *tuple-pattern-element-list* → [*tuple-pattern-element*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Patterns.html#//apple_ref/swift/grammar/tuple-pattern-element) | [*tuple-pattern-element*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Patterns.html#//apple_ref/swift/grammar/tuple-pattern-element) **,** [*tuple-pattern-element-list*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Patterns.html#//apple_ref/swift/grammar/tuple-pattern-element-list)
|
||||
> *tuple-pattern-element* → [*pattern*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Patterns.html#//apple_ref/swift/grammar/pattern)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 枚举用例模式 (Grammar of an enumeration case pattern)
|
||||
> *enum-case-pattern* → [*type-identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type-identifier) _opt_ **.** [*enum-case-name*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/enum-case-name) [*tuple-pattern*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Patterns.html#//apple_ref/swift/grammar/tuple-pattern) _opt_
|
||||
|
||||
<p></p>
|
||||
|
||||
> 类型转换模式 (Grammar of a type casting pattern)
|
||||
> *type-casting-pattern* → [*is-pattern*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Patterns.html#//apple_ref/swift/grammar/is-pattern) | [*as-pattern*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Patterns.html#//apple_ref/swift/grammar/as-pattern)
|
||||
> *is-pattern* → **is** [*type*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type)
|
||||
> *as-pattern* → [*pattern*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Patterns.html#//apple_ref/swift/grammar/pattern) **as** [*type*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 表达式模式 (Grammar of an expression pattern)
|
||||
> *expression-pattern* → [*expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression)
|
||||
|
||||
## 特性 (Attributes)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 特性语法 (Grammar of an attribute)
|
||||
> *attribute* → **@** [*attribute-name*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Attributes.html#//apple_ref/swift/grammar/attribute-name) [*attribute-argument-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Attributes.html#//apple_ref/swift/grammar/attribute-argument-clause) _opt_
|
||||
> *attribute-name* → [*identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier)
|
||||
> *attribute-argument-clause* → **(** [*balanced-tokens*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Attributes.html#//apple_ref/swift/grammar/balanced-tokens) _opt_ **)**
|
||||
> *attributes* → [*attribute*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Attributes.html#//apple_ref/swift/grammar/attribute) [*attributes*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Attributes.html#//apple_ref/swift/grammar/attributes) _opt_
|
||||
> *balanced-tokens* → [*balanced-token*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Attributes.html#//apple_ref/swift/grammar/balanced-token) [*balanced-tokens*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Attributes.html#//apple_ref/swift/grammar/balanced-tokens) _opt_
|
||||
> *balanced-token* → **(** [*balanced-tokens*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Attributes.html#//apple_ref/swift/grammar/balanced-tokens) _opt_ **)**
|
||||
> *balanced-token* → **[** [*balanced-tokens*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Attributes.html#//apple_ref/swift/grammar/balanced-tokens) _opt_ **]**
|
||||
> *balanced-token* → **{** [*balanced-tokens*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Attributes.html#//apple_ref/swift/grammar/balanced-tokens) _opt_ **}**
|
||||
> *balanced-token* → Any identifier, keyword, literal, or operator
|
||||
> *balanced-token* → Any punctuation except (, ), [, ], {, or }
|
||||
|
||||
## 表达式 (Expressions)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 表达式语法 (Grammar of an expression)
|
||||
> *expression* → [*prefix-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/prefix-expression) [*binary-expressions*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/binary-expressions) _opt_
|
||||
> *expression-list* → [*expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression) | [*expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression) **,** [*expression-list*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression-list)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 前缀表达式 (Grammar of a prefix expression)
|
||||
> *prefix-expression* → [*prefix-operator*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/prefix-operator) _opt_ [*postfix-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/postfix-expression)
|
||||
> *prefix-expression* → [*in-out-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/in-out-expression)
|
||||
> *in-out-expression* → **&** [*identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 二进制表达式 (Grammar of a binary expression)
|
||||
> *binary-expression* → [*binary-operator*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/binary-operator) [*prefix-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/prefix-expression)
|
||||
> *binary-expression* → [*assignment-operator*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/assignment-operator) [*prefix-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/prefix-expression)
|
||||
> *binary-expression* → [*conditional-operator*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/conditional-operator) [*prefix-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/prefix-expression)
|
||||
> *binary-expression* → [*type-casting-operator*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/type-casting-operator)
|
||||
> *binary-expressions* → [*binary-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/binary-expression) [*binary-expressions*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/binary-expressions) _opt_
|
||||
|
||||
<p></p>
|
||||
|
||||
> 赋值运算符 (Grammar of an assignment operator)
|
||||
> *assignment-operator* → **=**
|
||||
|
||||
<p></p>
|
||||
|
||||
> 条件运算符 (Grammar of a conditional operator)
|
||||
> *conditional-operator* → **?** [*expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression) **:**
|
||||
|
||||
<p></p>
|
||||
|
||||
> 类型转换运算符 (Grammar of a type-casting operator)
|
||||
> *type-casting-operator* → **is** [*type*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type) | **as** **?** _opt_ [*type*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 主表达式 (Grammar of a primary expression)
|
||||
> *primary-expression* → [*identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier) [*generic-argument-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/GenericParametersAndArguments.html#//apple_ref/swift/grammar/generic-argument-clause) _opt_
|
||||
> *primary-expression* → [*literal-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/literal-expression)
|
||||
> *primary-expression* → [*self-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/self-expression)
|
||||
> *primary-expression* → [*superclass-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/superclass-expression)
|
||||
> *primary-expression* → [*closure-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/closure-expression)
|
||||
> *primary-expression* → [*parenthesized-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/parenthesized-expression)
|
||||
> *primary-expression* → [*implicit-member-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/implicit-member-expression)
|
||||
> *primary-expression* → [*wildcard-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/wildcard-expression)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 文本表达式 (Grammar of a literal expression)
|
||||
> *literal-expression* → [*literal*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/literal)
|
||||
> *literal-expression* → [*array-literal*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/array-literal) | [*dictionary-literal*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/dictionary-literal)
|
||||
> *literal-expression* → **__FILE__** | **__LINE__** | **__COLUMN__** | **__FUNCTION__**
|
||||
> *array-literal* → **[** [*array-literal-items*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/array-literal-items) _opt_ **]**
|
||||
> *array-literal-items* → [*array-literal-item*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/array-literal-item) **,** _opt_ | [*array-literal-item*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/array-literal-item) **,** [*array-literal-items*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/array-literal-items)
|
||||
> *array-literal-item* → [*expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression)
|
||||
> *dictionary-literal* → **[** [*dictionary-literal-items*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/dictionary-literal-items) **]** | **[** **:** **]**
|
||||
> *dictionary-literal-items* → [*dictionary-literal-item*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/dictionary-literal-item) **,** _opt_ | [*dictionary-literal-item*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/dictionary-literal-item) **,** [*dictionary-literal-items*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/dictionary-literal-items)
|
||||
> *dictionary-literal-item* → [*expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression) **:** [*expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression)
|
||||
|
||||
<p></p>
|
||||
|
||||
> Self 表达式 (Grammar of a self expression)
|
||||
> *self-expression* → **self**
|
||||
> *self-expression* → **self** **.** [*identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier)
|
||||
> *self-expression* → **self** **[** [*expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression) **]**
|
||||
> *self-expression* → **self** **.** **init**
|
||||
|
||||
<p></p>
|
||||
|
||||
> 超类表达式 (Grammar of a superclass expression)
|
||||
> *superclass-expression* → [*superclass-method-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/superclass-method-expression) | [*superclass-subscript-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/superclass-subscript-expression) | [*superclass-initializer-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/superclass-initializer-expression)
|
||||
> *superclass-method-expression* → **super** **.** [*identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier)
|
||||
> *superclass-subscript-expression* → **super** **[** [*expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression) **]**
|
||||
> *superclass-initializer-expression* → **super** **.** **init**
|
||||
|
||||
<p></p>
|
||||
|
||||
> 闭包表达式 (Grammar of a closure expression)
|
||||
> *closure-expression* → **{** [*closure-signature*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/closure-signature) _opt_ [*statements*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/statements) **}**
|
||||
> *closure-signature* → [*parameter-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/parameter-clause) [*function-result*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/function-result) _opt_ **in**
|
||||
> *closure-signature* → [*identifier-list*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier-list) [*function-result*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/function-result) _opt_ **in**
|
||||
> *closure-signature* → [*capture-list*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/capture-list) [*parameter-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/parameter-clause) [*function-result*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/function-result) _opt_ **in**
|
||||
> *closure-signature* → [*capture-list*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/capture-list) [*identifier-list*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier-list) [*function-result*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/function-result) _opt_ **in**
|
||||
> *closure-signature* → [*capture-list*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/capture-list) **in**
|
||||
> *capture-list* → **[** [*capture-specifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/capture-specifier) [*expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression) **]**
|
||||
> *capture-specifier* → **weak** | **unowned** | **unowned(safe)** | **unowned(unsafe)**
|
||||
|
||||
<p></p>
|
||||
|
||||
> 隐式成员表达式 (Grammar of a implicit member expression)
|
||||
> *implicit-member-expression* → **.** [*identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 带圆括号的表达式 (Grammar of a parenthesized expression)
|
||||
> *parenthesized-expression* → **(** [*expression-element-list*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression-element-list) _opt_ **)**
|
||||
> *expression-element-list* → [*expression-element*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression-element) | [*expression-element*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression-element) **,** [*expression-element-list*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression-element-list)
|
||||
> *expression-element* → [*expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression) | [*identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier) **:** [*expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 通配符表达式 (Grammar of a wildcard expression)
|
||||
> *wildcard-expression* → **_**
|
||||
|
||||
<p></p>
|
||||
|
||||
> 后缀表达式 (Grammar of a postfix expression)
|
||||
> *postfix-expression* → [*primary-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/primary-expression)
|
||||
> *postfix-expression* → [*postfix-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/postfix-expression) [*postfix-operator*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/postfix-operator)
|
||||
> *postfix-expression* → [*function-call-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/function-call-expression)
|
||||
> *postfix-expression* → [*initializer-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/initializer-expression)
|
||||
> *postfix-expression* → [*explicit-member-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/explicit-member-expression)
|
||||
> *postfix-expression* → [*postfix-self-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/postfix-self-expression)
|
||||
> *postfix-expression* → [*dynamic-type-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/dynamic-type-expression)
|
||||
> *postfix-expression* → [*subscript-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/subscript-expression)
|
||||
> *postfix-expression* → [*forced-value-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/forced-value-expression)
|
||||
> *postfix-expression* → [*optional-chaining-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/optional-chaining-expression)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 函数调用表达式 (Grammar of a function call expression)
|
||||
> *function-call-expression* → [*postfix-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/postfix-expression) [*parenthesized-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/parenthesized-expression)
|
||||
> *function-call-expression* → [*postfix-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/postfix-expression) [*parenthesized-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/parenthesized-expression) _opt_ [*trailing-closure*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/trailing-closure)
|
||||
> *trailing-closure* → [*closure-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/closure-expression)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 初始化表达式 (Grammar of an initializer expression)
|
||||
> *initializer-expression* → [*postfix-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/postfix-expression) **.** **init**
|
||||
|
||||
<p></p>
|
||||
|
||||
> 显式成员表达式 (Grammar of an explicit member expression)
|
||||
> *explicit-member-expression* → [*postfix-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/postfix-expression) **.** [*decimal-digit*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/decimal-digit)
|
||||
> *explicit-member-expression* → [*postfix-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/postfix-expression) **.** [*identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier) [*generic-argument-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/GenericParametersAndArguments.html#//apple_ref/swift/grammar/generic-argument-clause) _opt_
|
||||
|
||||
<p></p>
|
||||
|
||||
> (Grammar of a self expression)
|
||||
> *postfix-self-expression* → [*postfix-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/postfix-expression) **.** **self**
|
||||
|
||||
<p></p>
|
||||
|
||||
> 动态类型表达式 (Grammar of a dynamic type expression)
|
||||
> *dynamic-type-expression* → [*postfix-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/postfix-expression) **.** **dynamicType**
|
||||
|
||||
<p></p>
|
||||
|
||||
> 附属脚本表达式 (Grammar of a subscript expression)
|
||||
> *subscript-expression* → [*postfix-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/postfix-expression) **[** [*expression-list*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression-list) **]**
|
||||
|
||||
<p></p>
|
||||
|
||||
> (Grammar of a forced-value expression)
|
||||
> *forced-value-expression* → [*postfix-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/postfix-expression) **!**
|
||||
|
||||
<p></p>
|
||||
|
||||
> 可选链表达式 (Grammar of an optional-chaining expression)
|
||||
> *optional-chaining-expression* → [*postfix-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/postfix-expression) **?**
|
||||
|
||||
## 词法结构 (Lexical Structure)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 标识符语法 (Grammar of an identifier)
|
||||
> *identifier* → [*identifier-head*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier-head) [*identifier-characters*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier-characters) _opt_
|
||||
> *identifier* → **`** [*identifier-head*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier-head) [*identifier-characters*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier-characters) _opt_ **`**
|
||||
> *identifier* → [*implicit-parameter-name*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/implicit-parameter-name)
|
||||
> *identifier-list* → [*identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier) | [*identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier) **,** [*identifier-list*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier-list)
|
||||
> *identifier-head* → Upper- or lowercase letter A through Z
|
||||
> *identifier-head* → U+00A8, U+00AA, U+00AD, U+00AF, U+00B2–U+00B5, or U+00B7–U+00BA
|
||||
> *identifier-head* → U+00BC–U+00BE, U+00C0–U+00D6, U+00D8–U+00F6, or U+00F8–U+00FF
|
||||
> *identifier-head* → U+0100–U+02FF, U+0370–U+167F, U+1681–U+180D, or U+180F–U+1DBF
|
||||
> *identifier-head* → U+1E00–U+1FFF
|
||||
> *identifier-head* → U+200B–U+200D, U+202A–U+202E, U+203F–U+2040, U+2054, or U+2060–U+206F
|
||||
> *identifier-head* → U+2070–U+20CF, U+2100–U+218F, U+2460–U+24FF, or U+2776–U+2793
|
||||
> *identifier-head* → U+2C00–U+2DFF or U+2E80–U+2FFF
|
||||
> *identifier-head* → U+3004–U+3007, U+3021–U+302F, U+3031–U+303F, or U+3040–U+D7FF
|
||||
> *identifier-head* → U+F900–U+FD3D, U+FD40–U+FDCF, U+FDF0–U+FE1F, or U+FE30–U+FE44
|
||||
> *identifier-head* → U+FE47–U+FFFD
|
||||
> *identifier-head* → U+10000–U+1FFFD, U+20000–U+2FFFD, U+30000–U+3FFFD, or U+40000–U+4FFFD
|
||||
> *identifier-head* → U+50000–U+5FFFD, U+60000–U+6FFFD, U+70000–U+7FFFD, or U+80000–U+8FFFD
|
||||
> *identifier-head* → U+90000–U+9FFFD, U+A0000–U+AFFFD, U+B0000–U+BFFFD, or U+C0000–U+CFFFD
|
||||
> *identifier-head* → U+D0000–U+DFFFD or U+E0000–U+EFFFD
|
||||
> *identifier-character* → Digit 0 through 9
|
||||
> *identifier-character* → U+0300–U+036F, U+1DC0–U+1DFF, U+20D0–U+20FF, or U+FE20–U+FE2F
|
||||
> *identifier-character* → [*identifier-head*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier-head)
|
||||
> *identifier-characters* → [*identifier-character*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier-character) [*identifier-characters*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier-characters) _opt_
|
||||
> *implicit-parameter-name* → **$** [*decimal-digits*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/decimal-digits)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 字面值语法 (Grammar of a literal)
|
||||
> *literal* → [*integer-literal*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/integer-literal) | [*floating-point-literal*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/floating-point-literal) | [*string-literal*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/string-literal)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 整形字面值 (Grammar of an integer literal)
|
||||
> *integer-literal* → [*binary-literal*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/binary-literal)
|
||||
> *integer-literal* → [*octal-literal*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/octal-literal)
|
||||
> *integer-literal* → [*decimal-literal*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/decimal-literal)
|
||||
> *integer-literal* → [*hexadecimal-literal*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-literal)
|
||||
> *binary-literal* → **0b** [*binary-digit*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/binary-digit) [*binary-literal-characters*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/binary-literal-characters) _opt_
|
||||
> *binary-digit* → Digit 0 or 1
|
||||
> *binary-literal-character* → [*binary-digit*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/binary-digit) | **_**
|
||||
> *binary-literal-characters* → [*binary-literal-character*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/binary-literal-character) [*binary-literal-characters*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/binary-literal-characters) _opt_
|
||||
> *octal-literal* → **0o** [*octal-digit*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/octal-digit) [*octal-literal-characters*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/octal-literal-characters) _opt_
|
||||
> *octal-digit* → Digit 0 through 7
|
||||
> *octal-literal-character* → [*octal-digit*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/octal-digit) | **_**
|
||||
> *octal-literal-characters* → [*octal-literal-character*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/octal-literal-character) [*octal-literal-characters*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/octal-literal-characters) _opt_
|
||||
> *decimal-literal* → [*decimal-digit*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/decimal-digit) [*decimal-literal-characters*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/decimal-literal-characters) _opt_
|
||||
> *decimal-digit* → Digit 0 through 9
|
||||
> *decimal-digits* → [*decimal-digit*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/decimal-digit) [*decimal-digits*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/decimal-digits) _opt_
|
||||
> *decimal-literal-character* → [*decimal-digit*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/decimal-digit) | **_**
|
||||
> *decimal-literal-characters* → [*decimal-literal-character*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/decimal-literal-character) [*decimal-literal-characters*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/decimal-literal-characters) _opt_
|
||||
> *hexadecimal-literal* → **0x** [*hexadecimal-digit*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-digit) [*hexadecimal-literal-characters*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-literal-characters) _opt_
|
||||
> *hexadecimal-digit* → Digit 0 through 9, a through f, or A through F
|
||||
> *hexadecimal-literal-character* → [*hexadecimal-digit*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-digit) | **_**
|
||||
> *hexadecimal-literal-characters* → [*hexadecimal-literal-character*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-literal-character) [*hexadecimal-literal-characters*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-literal-characters) _opt_
|
||||
|
||||
<p></p>
|
||||
|
||||
> 浮点型字面值 (Grammar of a floating-point literal)
|
||||
> *floating-point-literal* → [*decimal-literal*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/decimal-literal) [*decimal-fraction*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/decimal-fraction) _opt_ [*decimal-exponent*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/decimal-exponent) _opt_
|
||||
> *floating-point-literal* → [*hexadecimal-literal*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-literal) [*hexadecimal-fraction*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-fraction) _opt_ [*hexadecimal-exponent*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-exponent)
|
||||
> *decimal-fraction* → **.** [*decimal-literal*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/decimal-literal)
|
||||
> *decimal-exponent* → [*floating-point-e*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/floating-point-e) [*sign*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/sign) _opt_ [*decimal-literal*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/decimal-literal)
|
||||
> *hexadecimal-fraction* → **.** [*hexadecimal-literal*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-literal) _opt_
|
||||
> *hexadecimal-exponent* → [*floating-point-p*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/floating-point-p) [*sign*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/sign) _opt_ [*hexadecimal-literal*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-literal)
|
||||
> *floating-point-e* → **e** | **E**
|
||||
> *floating-point-p* → **p** | **P**
|
||||
> *sign* → **+** | **-**
|
||||
|
||||
<p></p>
|
||||
|
||||
> 字符串字面值 (Grammar of a string literal)
|
||||
> *string-literal* → **"** [*quoted-text*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/quoted-text) **"**
|
||||
> *quoted-text* → [*quoted-text-item*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/quoted-text-item) [*quoted-text*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/quoted-text) _opt_
|
||||
> *quoted-text-item* → [*escaped-character*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/escaped-character)
|
||||
> *quoted-text-item* → **\(** [*expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression) **)**
|
||||
> *quoted-text-item* → Any Unicode extended grapheme cluster except ", \, U+000A, or U+000D
|
||||
> *escaped-character* → **\0** | **\\** | **\t** | **\n** | **\r** | **\"** | **\'**
|
||||
> *escaped-character* → **\x** [*hexadecimal-digit*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-digit) [*hexadecimal-digit*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-digit)
|
||||
> *escaped-character* → **\u** [*hexadecimal-digit*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-digit) [*hexadecimal-digit*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-digit) [*hexadecimal-digit*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-digit) [*hexadecimal-digit*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-digit)
|
||||
> *escaped-character* → **\U** [*hexadecimal-digit*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-digit) [*hexadecimal-digit*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-digit) [*hexadecimal-digit*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-digit) [*hexadecimal-digit*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-digit) [*hexadecimal-digit*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-digit) [*hexadecimal-digit*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-digit) [*hexadecimal-digit*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-digit) [*hexadecimal-digit*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-digit)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 运算符语法 (Grammar of operators)
|
||||
> *operator* → [*operator-character*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/operator-character) [*operator*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/operator) _opt_
|
||||
> *operator-character* → **/** | **=** | **-** | **+** | **!** | ***** | **%** | **<** | **>** | **&** | **|** | **^** | **~** | **.**
|
||||
> *binary-operator* → [*operator*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/operator)
|
||||
> *prefix-operator* → [*operator*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/operator)
|
||||
> *postfix-operator* → [*operator*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/operator)
|
||||
|
||||
## 类型 (Types)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 类型 (Grammar of a type)
|
||||
> *type* → [*array-type*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/array-type) | [*function-type*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/function-type) | [*type-identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type-identifier) | [*tuple-type*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/tuple-type) | [*optional-type*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/optional-type) | [*implicitly-unwrapped-optional-type*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/implicitly-unwrapped-optional-type) | [*protocol-composition-type*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/protocol-composition-type) | [*metatype-type*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/metatype-type)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 类型标注 (Grammar of a type annotation)
|
||||
> *type-annotation* → **:** [*attributes*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Attributes.html#//apple_ref/swift/grammar/attributes) _opt_ [*type*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 类型标识 (Grammar of a type identifier)
|
||||
> *type-identifier* → [*type-name*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type-name) [*generic-argument-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/GenericParametersAndArguments.html#//apple_ref/swift/grammar/generic-argument-clause) _opt_ | [*type-name*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type-name) [*generic-argument-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/GenericParametersAndArguments.html#//apple_ref/swift/grammar/generic-argument-clause) _opt_ **.** [*type-identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type-identifier)
|
||||
> *type-name* → [*identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 元组类型 (Grammar of a tuple type)
|
||||
> *tuple-type* → **(** [*tuple-type-body*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/tuple-type-body) _opt_ **)**
|
||||
> *tuple-type-body* → [*tuple-type-element-list*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/tuple-type-element-list) **...** _opt_
|
||||
> *tuple-type-element-list* → [*tuple-type-element*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/tuple-type-element) | [*tuple-type-element*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/tuple-type-element) **,** [*tuple-type-element-list*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/tuple-type-element-list)
|
||||
> *tuple-type-element* → [*attributes*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Attributes.html#//apple_ref/swift/grammar/attributes) _opt_ **inout** _opt_ [*type*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type) | **inout** _opt_ [*element-name*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/element-name) [*type-annotation*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type-annotation)
|
||||
> *element-name* → [*identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 函数类型 (Grammar of a function type)
|
||||
> *function-type* → [*type*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type) **->** [*type*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 数组类型 (Grammar of an array type)
|
||||
> *array-type* → [*type*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type) **[** **]** | [*array-type*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/array-type) **[** **]**
|
||||
|
||||
<p></p>
|
||||
|
||||
> 可选类型 (Grammar of an optional type)
|
||||
> *optional-type* → [*type*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type) **?**
|
||||
|
||||
<p></p>
|
||||
|
||||
> 隐式解析可选类型 (Grammar of an implicitly unwrapped optional type)
|
||||
> *implicitly-unwrapped-optional-type* → [*type*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type) **!**
|
||||
|
||||
<p></p>
|
||||
|
||||
> 协议合成类型 (Grammar of a protocol composition type)
|
||||
> *protocol-composition-type* → **protocol** **<** [*protocol-identifier-list*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/protocol-identifier-list) _opt_ **>**
|
||||
> *protocol-identifier-list* → [*protocol-identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/protocol-identifier) | [*protocol-identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/protocol-identifier) **,** [*protocol-identifier-list*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/protocol-identifier-list)
|
||||
> *protocol-identifier* → [*type-identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type-identifier)
|
||||
|
||||
<p></p>
|
||||
|
||||
> 元类型 (Grammar of a metatype type)
|
||||
> *metatype-type* → [*type*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type) **.** **Type** | [*type*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type) **.** **Protocol**
|
||||
|
||||
<p></p>
|
||||
|
||||
> 类型继承子句 (Grammar of a type inheritance clause)
|
||||
> *type-inheritance-clause* → **:** [*type-inheritance-list*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type-inheritance-list)
|
||||
> *type-inheritance-list* → [*type-identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type-identifier) | [*type-identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type-identifier) **,** [*type-inheritance-list*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Types.html#//apple_ref/swift/grammar/type-inheritance-list)
|
||||
|
||||
@ -0,0 +1,375 @@
|
||||
# 语句
|
||||
|
||||
在 Swift 中，有两种类型的语句：简单语句和控制流语句。简单语句是最常见的，用于构造表达式和声明。控制流语句则用于控制程序执行的流程，Swift 中有三种类型的控制流语句：循环语句、分支语句和控制传递语句。
|
||||
|
||||
循环语句用于重复执行代码块；分支语句用于执行满足特定条件的代码块；控制传递语句则用于修改代码的执行顺序。在稍后的叙述中，将会详细地介绍每一种类型的控制流语句。
|
||||
|
||||
是否将分号(;)添加到语句的结尾处是可选的。但若要在同一行内写多条独立语句，请务必使用分号。
|
||||
|
||||
> GRAMMAR OF A STATEMENT
|
||||
|
||||
> *statement* → [*expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression)**;** *opt*
|
||||
|
||||
> *statement* → [*declaration*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/declaration)**;** *opt*
|
||||
|
||||
> *statement* → [*loop-statement*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/loop-statement)**;** *opt*
|
||||
|
||||
> *statement* → [*branch-statement*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/branch-statement)**;** *opt*
|
||||
|
||||
> *statement* → [*labeled-statement*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/labeled-statement)
|
||||
|
||||
> *statement* → [*control-transfer-statement*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/control-transfer-statement)**;** *opt*
|
||||
|
||||
> *statement* → [*statment*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/statement) [*statements*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/statements)**;** *opt*
|
||||
|
||||
## 循环语句
|
||||
|
||||
取决于特定的循环条件，循环语句允许重复执行代码块。Swift 提供四种类型的循环语句：`for`语句、`for-in`语句、`while`语句和`do-while`语句。
|
||||
|
||||
通过`break`语句和`continue`语句可以改变循环语句的控制流。有关这两条语句，请参考[*Break 语句*`待添加链接`]()和[*Continue 语句*`待添加链接`]()。
|
||||
|
||||
> GRAMMAR OF A LOOP STATEMENT
|
||||
|
||||
> *loop-statement* → [*for-statement*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/for-statement)
|
||||
|
||||
> *loop-statement* → [*for-in-statement*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/for-in-statement)
|
||||
|
||||
> *loop-statement* → [*while-statement*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/while-statement)
|
||||
|
||||
> *loop-statement* → [*do-while-statement*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/do-while-statement)
|
||||
|
||||
### For 语句
|
||||
|
||||
`for`语句允许在重复执行代码块的同时，递增一个计数器。
|
||||
|
||||
`for`语句的形式如下：
|
||||
|
||||
```swift
|
||||
for `initialzation`; `condition`; `increment` {
|
||||
`statements`
|
||||
}
|
||||
```
|
||||
|
||||
*initialzation*、*condition*和*increment*之间的分号，以及包围循环体*statements*的大括号都是不可省略的。
|
||||
|
||||
`for`语句的执行流程如下：
|
||||
|
||||
1. *initialzation*只会被执行一次，通常用于声明和初始化在接下来的循环中需要使用的变量。
|
||||
|
||||
2. 计算*condition*表达式：
|
||||
如果为真(`true`)，*statements*将会被执行，然后转到第3步。如果为假(`false`)，*statements*和*increment*都不会被执行，`for`至此执行完毕。
|
||||
|
||||
3. 计算*increment*表达式，然后转到第2步。
|
||||
|
||||
定义在*initialzation*中的变量仅在`for`语句的作用域以内有效。*condition*表达式的值的类型必须符合`LogicValue`协议。
|
||||
|
||||
> GRAMMAR OF A FOR STATEMENT
|
||||
|
||||
> *for-statement* → **for** [*for-init*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/for-init) *opt* **;** [*expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression) *opt* **;** [*expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression) *opt* [*code-block*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/code-block)
|
||||
|
||||
> *for-statement* → **for ( ** [*for-init*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/for-init) *opt* **;** [*expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression) *opt* **;** [*expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression) *opt* **)** [*code-block*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/code-block)
|
||||
|
||||
> *for-statement* → [*variable-declaration*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/variable-declaration) | [*expression-list*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression-list)
|
||||
|
||||
### For-In 语句
|
||||
|
||||
`for-in`语句允许在重复执行代码块的同时，迭代集合(或符合`Sequence`协议的任意类型)中的每一项。
|
||||
|
||||
`for-in`语句的形式如下：
|
||||
|
||||
```swift
|
||||
for `item` in `collection` {
|
||||
`statements`
|
||||
}
|
||||
```
|
||||
|
||||
`for-in`语句在循环开始前会调用*collection*表达式的`generate`方法来获取一个生成器类型（这是一个符合`Generator`协议的类型）的值。接下来循环开始，调用*collection*表达式的`next`方法。如果其返回值不是`None`，它将会被赋给*item*，然后执行*statements*，执行完毕后回到循环开始处；否则，将不会赋值给*item*也不会执行*statements*，`for-in`至此执行完毕。
|
||||
|
||||
> GRAMMAR OF A FOR-IN STATEMENT
|
||||
|
||||
> *for-in-statement* → **for** [*pattern*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Patterns.html#//apple_ref/swift/grammar/pattern) **in** [*expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression) [*code-block*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/code-block)
|
||||
|
||||
### While 语句
|
||||
|
||||
`while`语句允许重复执行代码块。
|
||||
|
||||
`while`语句的形式如下：
|
||||
|
||||
```swift
|
||||
while `condition` {
|
||||
`statements`
|
||||
}
|
||||
```
|
||||
|
||||
`while`语句的执行流程如下：
|
||||
|
||||
1. 计算*condition*表达式：
|
||||
如果为真(`true`)，转到第2步。如果为假(`false`)，`while`至此执行完毕。
|
||||
|
||||
2. 执行*statements*，然后转到第1步。
|
||||
|
||||
由于*condition*的值在*statements*执行前就已计算出，因此`while`语句中的*statements*可能会被执行若干次，也可能不会被执行。
|
||||
|
||||
*condition*表达式的值的类型必须符合`LogicValue`协议。同时，*condition*表达式也可以使用可选绑定，请参考[可选绑定`待添加链接`]()。
|
||||
|
||||
> GRAMMAR OF A WHILE STATEMENT
|
||||
|
||||
> *while-statement* → **while** [*while-condition*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/while-condition) [*code-block*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/code-block)
|
||||
|
||||
> *while-condition* → [*expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression) | [*declaration*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/declaration)
|
||||
|
||||
### Do-While 语句
|
||||
|
||||
`do-while`语句允许代码块被执行一次或多次。
|
||||
|
||||
`do-while`语句的形式如下：
|
||||
|
||||
```swift
|
||||
do {
|
||||
`statements`
|
||||
} while `condition`
|
||||
```
|
||||
|
||||
`do-while`语句的执行流程如下：
|
||||
|
||||
1. 执行*statements*，然后转到第2步。
|
||||
|
||||
2. 计算*condition*表达式：
|
||||
如果为真(`true`)，转到第1步。如果为假(`false`)，`do-while`至此执行完毕。
|
||||
|
||||
由于*condition*表达式的值是在*statements*表达式执行后才计算出，因此*do-while*语句中的*statements*至少会被执行一次。
|
||||
|
||||
*condition*表达式的值的类型必须符合`LogicValue`协议。同时，*condition*表达式也可以使用可选绑定，请参考[可选绑定`待添加链接`]()。
|
||||
|
||||
> GRAMMAR OF A DO-WHILE STATEMENT
|
||||
|
||||
> *do-while-statement* → **do** [*code-block*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/code-block) **while** [*while-condition*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/while-condition)
|
||||
|
||||
## 分支语句
|
||||
|
||||
取决于一个或者多个条件的值，分支语句允许程序执行指定部分的代码。显然，分支语句中条件的值将会决定如何分支以及执行哪一块代码。Swift 提供两种类型的分支语句：`if`语句和`switch`语句。
|
||||
|
||||
`switch`语句中的控制流可以用`break`语句修改，请参考[Break 语句`待添加链接`]()。
|
||||
|
||||
> GRAMMAR OF A BRANCH STATEMENT
|
||||
|
||||
> *branch-statement* → [*if-statement*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/if-statement)
|
||||
|
||||
> *branch-statement* → [*switch-statement*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/switch-statement)
|
||||
|
||||
### If 语句
|
||||
|
||||
取决于一个或多个条件的值，`if`语句将决定执行哪一块代码。
|
||||
|
||||
`if`语句有两种标准形式，在这两种形式里都必须有大括号。
|
||||
|
||||
第一种形式是当且仅当条件为真时执行代码，像下面这样：
|
||||
|
||||
```swift
|
||||
if `condition` {
|
||||
`statements`
|
||||
}
|
||||
```
|
||||
|
||||
第二种形式是在第一种形式的基础上添加*else语句*，当只有一个*else语句*时，像下面这样：
|
||||
|
||||
```swift
|
||||
if `condition` {
|
||||
`statements to execute if condition is true`
|
||||
} else {
|
||||
`statements to execute if condition is false`
|
||||
}
|
||||
```
|
||||
|
||||
同时，*else语句*也可包含`if`语句，从而形成一条链来测试更多的条件，像下面这样：
|
||||
|
||||
```swift
|
||||
if `condition 1` {
|
||||
`statements to execute if condition 1 is true`
|
||||
} else if `condition 2` {
|
||||
`statements to execute if condition 2 is true`
|
||||
}
|
||||
else {
|
||||
`statements to execute if both conditions are false`
|
||||
}
|
||||
```
|
||||
|
||||
`if`语句中条件的值的类型必须符合`LogicValue`协议。同时，条件也可以使用可选绑定，请参考[可选绑定`待添加链接`]()。
|
||||
|
||||
> GRAMMAR OF AN IF STATEMENT
|
||||
|
||||
> *if-statement* → **if** [*if-condition*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/if-condition) [*code-block*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/code-block) [*else-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/else-clause) *opt*
|
||||
|
||||
> *if-condition* → [*expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression) | [*declaration*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/declaration)
|
||||
|
||||
> *else-clause* → **else** [*code-block*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/code-block) | **else** [*if-statement*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/if-statement) *opt*
|
||||
|
||||
### Switch 语句
|
||||
|
||||
取决于`switch`语句的控制表达式(*control expression*)，`switch`语句将决定执行哪一块代码。
|
||||
|
||||
`switch`语句的形式如下：
|
||||
|
||||
```swift
|
||||
switch `control expression` {
|
||||
case `pattern 1`:
|
||||
`statements`
|
||||
case `pattern 2` where `condition`:
|
||||
`statements`
|
||||
case `pattern 3` where `condition`,
|
||||
`pattern 4` where `condition`:
|
||||
`statements`
|
||||
default:
|
||||
`statements`
|
||||
}
|
||||
```
|
||||
|
||||
`switch`语句的*控制表达式(control expression)*会首先被计算，然后与每一个*case*的模式(pattern)进行匹配。如果匹配成功，程序将会执行对应的*case*块里的*statements*。另外，每一个*case*块都不能为空，也就是说在每一个*case*块中至少有一条语句。如果你不想在匹配到的*case*块中执行代码，只需在块里写一条`break`语句即可。
|
||||
|
||||
可以用作控制表达式的值是十分灵活的，除了标量类型(scalar types，如`Int`、`Character`)外，你可以使用任何类型的值，包括浮点数、字符串、元组、自定义类的实例和可选(optional)类型，甚至是枚举类型中的成员值和指定的范围(range)等。关于在`switch`语句中使用这些类型，请参考[控制流`待添加链接`]()一章的[Switch`待添加链接`]()。
|
||||
|
||||
你可以在模式后面添加一个起保护作用的表达式(guard expression)。*起保护作用的表达式*是这样构成的：关键字`where`后面跟着一个作为额外测试条件的表达式。因此，当且仅当*控制表达式*匹配一个*case*的某个模式且起保护作用的表达式为真时，对应*case*块中的*statements*才会被执行。在下面的例子中，*控制表达式*只会匹配含两个相等元素的元组，如`(1, 1)`：
|
||||
|
||||
```swift
|
||||
case let (x, y) where x == y:
|
||||
}
|
||||
```
|
||||
|
||||
正如上面这个例子，也可以在模式中使用`let`（或`var`）语句来绑定常量（或变量）。这些常量（或变量）可以在其对应的起保护作用的表达式和其对应的*case*块里的代码中引用。但是，如果*case*中有多个模式匹配控制表达式，那么这些模式都不能绑定常量（或变量）。
|
||||
|
||||
`switch`语句也可以包含默认(`default`)块，只有其它*case*块都无法匹配控制表达式时，默认块中的代码才会被执行。一个`switch`语句只能有一个默认块，而且必须在`switch`语句的最后面。
|
||||
|
||||
尽管模式匹配操作实际的执行顺序，特别是模式的计算顺序是不可知的，但是 Swift 规定`switch`语句中的模式匹配的顺序和书写源代码的顺序保持一致。因此，当多个模式含有相同的值且能够匹配控制表达式时，程序只会执行源代码中第一个匹配的*case*块中的代码。
|
||||
|
||||
#### Switch 语句必须是完备的
|
||||
|
||||
在 Swift 中，`switch`语句中控制表达式的每一个可能的值都必须至少有一个`case`块与之对应。在某些情况下（例如，表达式的类型是`Int`），你可以使用默认块满足该要求。
|
||||
|
||||
#### 不存在隐式的贯穿(fall through)
|
||||
|
||||
当匹配的*case*块中的代码执行完毕后，程序会终止`switch`语句，而不会继续执行下一个*case*块。这就意味着，如果你想执行下一个*case*块，需要显式地在你需要的*case*块里使用`fallthrough`语句。关于`fallthrough`语句的更多信息，请参考[Fallthrough 语句`待添加链接`]()。
|
||||
|
||||
> GRAMMAR OF A SWITCH STATEMENT
|
||||
|
||||
> *switch-statement* → **switch** [*expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression) **{** [*switch-cases*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/switch-cases) *opt* **}**
|
||||
|
||||
> *switch-cases* → [*switch-case*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/switch-case) [*switch-cases*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/switch-cases) *opt*
|
||||
|
||||
> *switch-case* → [*case-label*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/case-label) [*statement*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/statements) | [*default-label*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/default-label) [*statements*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/statements)
|
||||
|
||||
> *switch-case* → [*case-label*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/case-label) **;** | [*default-label*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/default-label) **;**
|
||||
|
||||
> *case-label* → **case** [*case-item-list*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/case-item-list) **:**
|
||||
|
||||
> *case-item-list* → [*pattern*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Patterns.html#//apple_ref/swift/grammar/pattern) [*guard-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/guard-clause) *opt* | [*pattern*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Patterns.html#//apple_ref/swift/grammar/pattern) [*guard-clause*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/guard-clause) *opt*, [*case-item-list*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/case-item-list)
|
||||
|
||||
> *default-label* → **default :**
|
||||
|
||||
> *guard-clause* → **where** [*guard-expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/guard-expression)
|
||||
|
||||
> *guard-expression* → [*expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression)
|
||||
|
||||
## 带标签的语句
|
||||
|
||||
你可以在循环语句或`switch`语句前面加上*标签*，它由标签名和紧随其后的冒号(:)组成。在`break`和`continue`后面跟上标签名可以显式地在循环语句或`switch`语句中更改控制流，把控制权传递给指定标签标记的语句。关于这两条语句用法，请参考[Break 语句`待添加链接`]()和[Continue 语句`待添加链接`]()。
|
||||
|
||||
标签的作用域是该标签所标记的语句之后的所有语句。你可以不使用带标签的语句，但只要使用它，标签名就必唯一。
|
||||
|
||||
关于使用带标签的语句的例子，请参考[控制流`待添加链接`]()一章的[带标签的语句`待添加链接`]()。
|
||||
|
||||
> GRAMMAR OF A LABELED STATEMENT
|
||||
|
||||
> *labeled-statement* → [*statement-label*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/statement-label) [*loop-statement*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/loop-statement) | [*statement-label*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/statement-label) [*switch-statement*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/switch-statement)
|
||||
|
||||
> *statement-label* → [*label-name*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/label-name) **:**
|
||||
|
||||
> *label-name* → [*identifier*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier)
|
||||
|
||||
## 控制传递语句
|
||||
|
||||
通过无条件地把控制权从一片代码传递到另一片代码，控制传递语句能够改变代码执行的顺序。Swift 提供四种类型的控制传递语句：`break`语句、`continue`语句、`fallthrough`语句和`return`语句。
|
||||
|
||||
> GRAMMAR OF A CONTROL TRANSER STATEMENT
|
||||
|
||||
> *control-transfer-statement* → [*break-statement*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/break-statement)
|
||||
|
||||
> *control-transfer-statement* → [*continue-statement*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/continue-statement)
|
||||
|
||||
> *control-transfer-statement* → [*fallthrough-statement*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/fallthrough-statement)
|
||||
|
||||
> *control-transfer-statement* → [*return-statement*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/return-statement)
|
||||
|
||||
### Break 语句
|
||||
|
||||
`break`语句用于终止循环或`switch`语句的执行。使用`break`语句时，可以只写`break`这个关键词，也可以在`break`后面跟上标签名(label name)，像下面这样：
|
||||
|
||||
```swift
|
||||
break
|
||||
break `label name`
|
||||
```
|
||||
|
||||
当`break`语句后面带标签名时，可用于终止由这个标签标记的循环或`switch`语句的执行。
|
||||
|
||||
而当只写`break`时，则会终止`switch`语句或上下文中包含`break`语句的最内层循环的执行。
|
||||
|
||||
在这两种情况下，控制权都会被传递给循环或`switch`语句外面的第一行语句。
|
||||
|
||||
关于使用`break`语句的例子，请参考[控制流`待添加链接`]()一章的[Break`待添加链接`]()和[带标签的语句`待添加链接`]()。
|
||||
|
||||
> GRAMMAR OF A BREAK STATEMENT
|
||||
|
||||
> *break-statement* → **break** [*label-name*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/label-name) *opt*
|
||||
|
||||
### Continue 语句
|
||||
|
||||
`continue`语句用于终止循环中当前迭代的执行，但不会终止该循环的执行。使用`continue`语句时，可以只写`continue`这个关键词，也可以在`continue`后面跟上标签名(label name)，像下面这样：
|
||||
|
||||
```swift
|
||||
continue
|
||||
continue `label name`
|
||||
```
|
||||
|
||||
当`continue`语句后面带标签名时，可用于终止由这个标签标记的循环中当前迭代的执行。
|
||||
|
||||
而当只写`break`时，可用于终止上下文中包含`continue`语句的最内层循环中当前迭代的执行。
|
||||
|
||||
在这两种情况下，控制权都会被传递给循环外面的第一行语句。
|
||||
|
||||
在`for`语句中，`continue`语句执行后，*increment*表达式还是会被计算，这是因为每次循环体执行完毕后*increment*表达式都会被计算。
|
||||
|
||||
关于使用`continue`语句的例子，请参考[控制流`待添加链接`]()一章的[Continue`待添加链接`]()和[带标签的语句`待添加链接`]()。
|
||||
|
||||
> GRAMMAR OF A CONTINUE STATEMENT
|
||||
|
||||
> *continue-statement* → **continue** [*label-name*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Statements.html#//apple_ref/swift/grammar/label-name) *opt*
|
||||
|
||||
### Fallthrough 语句
|
||||
|
||||
`fallthrough`语句用于在`switch`语句中传递控制权。`fallthrough`语句会把控制权从`switch`语句中的一个`case`传递给下一个`case`。这种传递是无条件的，即使下一个`case`的值与`switch`语句的控制表达式的值不匹配。
|
||||
|
||||
`fallthrough`语句可出现在`switch`语句中的任意`case`里，但不能出现在最后一个'case'块。同时，`fallthrough`语句也不能把控制权传递给使用了可选绑定的`case`块。
|
||||
|
||||
关于在`switch`语句中使用`fallthrough`语句的例子，请参考[控制流`待添加链接`]()一章的[控制传递语句`待添加链接`]()。
|
||||
|
||||
> GRAMMAR OF A FALLTRHOUGH STATEMENT
|
||||
|
||||
> *continue-statement* → **fallthrough**
|
||||
|
||||
### Return 语句
|
||||
|
||||
`return`语句用于在函数或方法的实现中将控制权传递给调用者，接着程序将会从调用者的位置继续向下执行。
|
||||
|
||||
使用`return`语句时，可以只写`return`这个关键词，也可以在`return`后面跟上表达式，像下面这样：
|
||||
|
||||
```swift
|
||||
return
|
||||
return `表达式`
|
||||
```
|
||||
|
||||
当`return`语句后面带表达式时，表达式的值将会返回给调用者。如果表达式值的类型与调用者期望的类型不匹配，Swift 则会在返回表达式的值之前将表达式值的类型转换为调用者期望的类型。
|
||||
|
||||
而当只写`return`时，仅仅是将控制权从该函数或方法传递给调用者，而不返回一个值。（这就是说，该函数或方法的返回类型为`Void`或`()`）
|
||||
|
||||
> GRAMMAR OF A RETURN STATEMENT
|
||||
|
||||
> *return-statement* → **return** [*expression*](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression) *opt*
|
||||
Reference in New Issue
Block a user