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<i class="fa fa-check"></i> <b>1.</b> 欢迎使用 Swift
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<i class="fa fa-check"></i> <b>1.1.</b> 关于 Swift
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<i class="fa fa-check"></i> <b>1.2.</b> Swift 初见
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<i class="fa fa-check"></i> <b>2.</b> Swift 教程
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<i class="fa fa-check"></i> <b>2.1.</b> 基础部分
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<li class="chapter " data-level="2.2" data-path="chapter2/02_Basic_Operators.html">
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<i class="fa fa-check"></i> <b>2.2.</b> 基本运算符
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</a>
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<i class="fa fa-check"></i> <b>2.3.</b> 字符串和字符
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</a>
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<a href="../chapter2/04_Collection_Types.html">
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<i class="fa fa-check"></i> <b>2.4.</b> 集合类型
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</a>
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<li class="chapter " data-level="2.5" data-path="chapter2/05_Control_Flow.html">
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<a href="../chapter2/05_Control_Flow.html">
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<i class="fa fa-check"></i> <b>2.5.</b> 控制流
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</a>
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<li class="chapter " data-level="2.6" data-path="chapter2/06_Functions.html">
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<a href="../chapter2/06_Functions.html">
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<i class="fa fa-check"></i> <b>2.6.</b> 函数
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</a>
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<li class="chapter " data-level="2.7" data-path="chapter2/07_Closures.html">
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<a href="../chapter2/07_Closures.html">
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<i class="fa fa-check"></i> <b>2.7.</b> 闭包
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</a>
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<li class="chapter " data-level="2.8" data-path="chapter2/08_Enumerations.html">
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<a href="../chapter2/08_Enumerations.html">
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<i class="fa fa-check"></i> <b>2.8.</b> 枚举
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</a>
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<li class="chapter " data-level="2.9" data-path="chapter2/09_Classes_and_Structures.html">
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<a href="../chapter2/09_Classes_and_Structures.html">
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<i class="fa fa-check"></i> <b>2.9.</b> 类和结构体
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</a>
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</li>
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<li class="chapter " data-level="2.10" data-path="chapter2/10_Properties.html">
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<a href="../chapter2/10_Properties.html">
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<i class="fa fa-check"></i> <b>2.10.</b> 属性
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</a>
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</li>
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<li class="chapter " data-level="2.11" data-path="chapter2/11_Methods.html">
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<a href="../chapter2/11_Methods.html">
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<i class="fa fa-check"></i> <b>2.11.</b> 方法
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</a>
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</li>
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<li class="chapter " data-level="2.12" data-path="chapter2/12_Subscripts.html">
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<a href="../chapter2/12_Subscripts.html">
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<i class="fa fa-check"></i> <b>2.12.</b> 附属脚本
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</a>
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</li>
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<li class="chapter " data-level="2.13" data-path="chapter2/13_Inheritance.html">
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<a href="../chapter2/13_Inheritance.html">
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<i class="fa fa-check"></i> <b>2.13.</b> 继承
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</a>
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</li>
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<li class="chapter " data-level="2.14" data-path="chapter2/14_Initialization.html">
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<a href="../chapter2/14_Initialization.html">
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<i class="fa fa-check"></i> <b>2.14.</b> 构造过程
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</a>
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</li>
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<li class="chapter " data-level="2.15" data-path="chapter2/15_Deinitialization.html">
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<a href="../chapter2/15_Deinitialization.html">
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<i class="fa fa-check"></i> <b>2.15.</b> 析构过程
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</a>
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</li>
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<li class="chapter " data-level="2.16" data-path="chapter2/16_Automatic_Reference_Counting.html">
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<a href="../chapter2/16_Automatic_Reference_Counting.html">
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<i class="fa fa-check"></i> <b>2.16.</b> 自动引用计数
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</a>
|
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|
||
|
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</li>
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|
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<li class="chapter " data-level="2.17" data-path="chapter2/17_Optional_Chaining.html">
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<a href="../chapter2/17_Optional_Chaining.html">
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<i class="fa fa-check"></i> <b>2.17.</b> 可选链
|
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</a>
|
||
|
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|
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</li>
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|
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<li class="chapter " data-level="2.18" data-path="chapter2/18_Type_Casting.html">
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<a href="../chapter2/18_Type_Casting.html">
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<i class="fa fa-check"></i> <b>2.18.</b> 类型检查
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</a>
|
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|
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</li>
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|
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<li class="chapter " data-level="2.19" data-path="chapter2/19_Nested_Types.html">
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<a href="../chapter2/19_Nested_Types.html">
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<i class="fa fa-check"></i> <b>2.19.</b> 嵌套类型
|
||
</a>
|
||
|
||
|
||
</li>
|
||
|
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<li class="chapter " data-level="2.20" data-path="chapter2/20_Extensions.html">
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<a href="../chapter2/20_Extensions.html">
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<i class="fa fa-check"></i> <b>2.20.</b> 扩展
|
||
</a>
|
||
|
||
|
||
</li>
|
||
|
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<li class="chapter " data-level="2.21" data-path="chapter2/21_Protocols.html">
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|
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<a href="../chapter2/21_Protocols.html">
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<i class="fa fa-check"></i> <b>2.21.</b> 协议
|
||
</a>
|
||
|
||
|
||
</li>
|
||
|
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<li class="chapter " data-level="2.22" data-path="chapter2/22_Generics.html">
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|
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<a href="../chapter2/22_Generics.html">
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<i class="fa fa-check"></i> <b>2.22.</b> 泛型
|
||
</a>
|
||
|
||
|
||
</li>
|
||
|
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<li class="chapter " data-level="2.23" data-path="chapter2/23_Advanced_Operators.html">
|
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|
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<a href="../chapter2/23_Advanced_Operators.html">
|
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<i class="fa fa-check"></i> <b>2.23.</b> 高级操作符
|
||
</a>
|
||
|
||
|
||
</li>
|
||
|
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|
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</ul>
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</li>
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<li class="chapter " data-level="3" data-path="chapter3/chapter3.html">
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<a href="../chapter3/chapter3.html">
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<i class="fa fa-check"></i> <b>3.</b> 语言参考
|
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</a>
|
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|
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<ul class="articles">
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<li class="chapter " data-level="3.1" data-path="chapter3/01_About_the_Language_Reference.html">
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<a href="../chapter3/01_About_the_Language_Reference.html">
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<i class="fa fa-check"></i> <b>3.1.</b> 关于语言参考
|
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</a>
|
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|
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|
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</li>
|
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|
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<li class="chapter " data-level="3.2" data-path="chapter3/02_Lexical_Structure.html">
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<a href="../chapter3/02_Lexical_Structure.html">
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<i class="fa fa-check"></i> <b>3.2.</b> 词法结构
|
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</a>
|
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</li>
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<li class="chapter " data-level="3.3" data-path="chapter3/03_Types.html">
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<a href="../chapter3/03_Types.html">
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<i class="fa fa-check"></i> <b>3.3.</b> 类型
|
||
</a>
|
||
|
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|
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</li>
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|
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<li class="chapter " data-level="3.4" data-path="chapter3/04_Expressions.html">
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<a href="../chapter3/04_Expressions.html">
|
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<i class="fa fa-check"></i> <b>3.4.</b> 表达式
|
||
</a>
|
||
|
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|
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</li>
|
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|
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<li class="chapter " data-level="3.5" data-path="chapter3/10_Statements.html">
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<a href="../chapter3/10_Statements.html">
|
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<i class="fa fa-check"></i> <b>3.5.</b> 语句
|
||
</a>
|
||
|
||
|
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</li>
|
||
|
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<li class="chapter " data-level="3.6" data-path="chapter3/05_Declarations.html">
|
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|
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<a href="../chapter3/05_Declarations.html">
|
||
<i class="fa fa-check"></i> <b>3.6.</b> 声明
|
||
</a>
|
||
|
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|
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</li>
|
||
|
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<li class="chapter " data-level="3.7" data-path="chapter3/06_Attributes.html">
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|
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<a href="../chapter3/06_Attributes.html">
|
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<i class="fa fa-check"></i> <b>3.7.</b> 特性
|
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</a>
|
||
|
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|
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</li>
|
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|
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<li class="chapter " data-level="3.8" data-path="chapter3/07_Patterns.html">
|
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|
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<a href="../chapter3/07_Patterns.html">
|
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<i class="fa fa-check"></i> <b>3.8.</b> 模式
|
||
</a>
|
||
|
||
|
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</li>
|
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|
||
<li class="chapter " data-level="3.9" data-path="chapter3/08_Generic_Parameters_and_Arguments.html">
|
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|
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<a href="../chapter3/08_Generic_Parameters_and_Arguments.html">
|
||
<i class="fa fa-check"></i> <b>3.9.</b> 泛型参数
|
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</a>
|
||
|
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|
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</li>
|
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|
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<li class="chapter " data-level="3.10" data-path="chapter3/09_Summary_of_the_Grammar.html">
|
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|
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<a href="../chapter3/09_Summary_of_the_Grammar.html">
|
||
<i class="fa fa-check"></i> <b>3.10.</b> 语法总结
|
||
</a>
|
||
|
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|
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</li>
|
||
|
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|
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</ul>
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||
<a href="../chapter1/01_swift.html" title="关于 Swift" class="chapter done " data-progress="1.1" style="left: 5.2631578947368425%;"></a>
|
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|
||
<a href="../chapter1/02_a_swift_tour.html" title="Swift 初见" class="chapter done " data-progress="1.2" style="left: 7.894736842105263%;"></a>
|
||
|
||
<a href="../chapter2/chapter2.html" title="Swift 教程" class="chapter done new-chapter" data-progress="2" style="left: 10.526315789473685%;"></a>
|
||
|
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<a href="../chapter2/01_The_Basics.html" title="基础部分" class="chapter done " data-progress="2.1" style="left: 13.157894736842104%;"></a>
|
||
|
||
<a href="../chapter2/10_Properties.html" title="属性" class="chapter done " data-progress="2.10" style="left: 15.789473684210526%;"></a>
|
||
|
||
<a href="../chapter2/11_Methods.html" title="方法" class="chapter done " data-progress="2.11" style="left: 18.42105263157895%;"></a>
|
||
|
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<a href="../chapter2/12_Subscripts.html" title="附属脚本" class="chapter done " data-progress="2.12" style="left: 21.05263157894737%;"></a>
|
||
|
||
<a href="../chapter2/13_Inheritance.html" title="继承" class="chapter done " data-progress="2.13" style="left: 23.68421052631579%;"></a>
|
||
|
||
<a href="../chapter2/14_Initialization.html" title="构造过程" class="chapter done " data-progress="2.14" style="left: 26.31578947368421%;"></a>
|
||
|
||
<a href="../chapter2/15_Deinitialization.html" title="析构过程" class="chapter done " data-progress="2.15" style="left: 28.94736842105263%;"></a>
|
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|
||
<a href="../chapter2/16_Automatic_Reference_Counting.html" title="自动引用计数" class="chapter done " data-progress="2.16" style="left: 31.57894736842105%;"></a>
|
||
|
||
<a href="../chapter2/17_Optional_Chaining.html" title="可选链" class="chapter done " data-progress="2.17" style="left: 34.21052631578947%;"></a>
|
||
|
||
<a href="../chapter2/18_Type_Casting.html" title="类型检查" class="chapter done " data-progress="2.18" style="left: 36.8421052631579%;"></a>
|
||
|
||
<a href="../chapter2/19_Nested_Types.html" title="嵌套类型" class="chapter done " data-progress="2.19" style="left: 39.473684210526315%;"></a>
|
||
|
||
<a href="../chapter2/02_Basic_Operators.html" title="基本运算符" class="chapter done " data-progress="2.2" style="left: 42.10526315789474%;"></a>
|
||
|
||
<a href="../chapter2/20_Extensions.html" title="扩展" class="chapter done " data-progress="2.20" style="left: 44.73684210526316%;"></a>
|
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|
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<a href="../chapter2/21_Protocols.html" title="协议" class="chapter done " data-progress="2.21" style="left: 47.36842105263158%;"></a>
|
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|
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<a href="../chapter2/22_Generics.html" title="泛型" class="chapter done " data-progress="2.22" style="left: 50%;"></a>
|
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|
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<a href="../chapter2/23_Advanced_Operators.html" title="高级操作符" class="chapter done " data-progress="2.23" style="left: 52.63157894736842%;"></a>
|
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|
||
<a href="../chapter2/03_Strings_and_Characters.html" title="字符串和字符" class="chapter done " data-progress="2.3" style="left: 55.26315789473684%;"></a>
|
||
|
||
<a href="../chapter2/04_Collection_Types.html" title="集合类型" class="chapter done " data-progress="2.4" style="left: 57.89473684210526%;"></a>
|
||
|
||
<a href="../chapter2/05_Control_Flow.html" title="控制流" class="chapter done " data-progress="2.5" style="left: 60.526315789473685%;"></a>
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||
|
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<a href="../chapter2/06_Functions.html" title="函数" class="chapter done " data-progress="2.6" style="left: 63.1578947368421%;"></a>
|
||
|
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<a href="../chapter2/07_Closures.html" title="闭包" class="chapter done " data-progress="2.7" style="left: 65.78947368421052%;"></a>
|
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|
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<a href="../chapter2/08_Enumerations.html" title="枚举" class="chapter done " data-progress="2.8" style="left: 68.42105263157895%;"></a>
|
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|
||
<a href="../chapter2/09_Classes_and_Structures.html" title="类和结构体" class="chapter done " data-progress="2.9" style="left: 71.05263157894737%;"></a>
|
||
|
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<a href="../chapter3/chapter3.html" title="语言参考" class="chapter done new-chapter" data-progress="3" style="left: 73.6842105263158%;"></a>
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<a href="../chapter3/01_About_the_Language_Reference.html" title="关于语言参考" class="chapter done " data-progress="3.1" style="left: 76.3157894736842%;"></a>
|
||
|
||
<a href="../chapter3/09_Summary_of_the_Grammar.html" title="语法总结" class="chapter done " data-progress="3.10" style="left: 78.94736842105263%;"></a>
|
||
|
||
<a href="../chapter3/02_Lexical_Structure.html" title="词法结构" class="chapter done " data-progress="3.2" style="left: 81.57894736842105%;"></a>
|
||
|
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<a href="../chapter3/03_Types.html" title="类型" class="chapter " data-progress="3.3" style="left: 84.21052631578948%;"></a>
|
||
|
||
<a href="../chapter3/04_Expressions.html" title="表达式" class="chapter " data-progress="3.4" style="left: 86.84210526315789%;"></a>
|
||
|
||
<a href="../chapter3/10_Statements.html" title="语句" class="chapter " data-progress="3.5" style="left: 89.47368421052632%;"></a>
|
||
|
||
<a href="../chapter3/05_Declarations.html" title="声明" class="chapter " data-progress="3.6" style="left: 92.10526315789474%;"></a>
|
||
|
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<a href="../chapter3/06_Attributes.html" title="特性" class="chapter " data-progress="3.7" style="left: 94.73684210526316%;"></a>
|
||
|
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<a href="../chapter3/07_Patterns.html" title="模式" class="chapter " data-progress="3.8" style="left: 97.36842105263158%;"></a>
|
||
|
||
<a href="../chapter3/08_Generic_Parameters_and_Arguments.html" title="泛型参数" class="chapter " data-progress="3.9" style="left: 100%;"></a>
|
||
|
||
</div>
|
||
</div>
|
||
|
||
<div class="page-inner">
|
||
|
||
<section class="normal" id="section-gitbook_332">
|
||
|
||
<h1 id="-">语法结构</h1>
|
||
<p>本页包含内容：</p>
|
||
<ul>
|
||
<li>空白与注释（<em>Whitespace and Comments</em>）</li>
|
||
<li>标识符（<em>Identifiers</em>）</li>
|
||
<li>关键字（<em>Keywords</em>）</li>
|
||
<li>字面量（<em>Literals</em>）</li>
|
||
<li>运算符（<em>Operators</em>）</li>
|
||
</ul>
|
||
<p>Swift 的“语法结构（<em>lexical structure</em>）”描述了如何在该语言中用字符序列构建合法标记，组成该语言中最底层的代码块，并在之后的章节中用于描述语言的其他部分。</p>
|
||
<p>通常，标记在随后介绍的语法约束下，由 Swift 源文件的输入文本中提取可能的最长子串生成。这种方法称为“最长匹配项（<em>longest match</em>）”，或者“最大适合”（<em>maximal munch</em>）。</p>
|
||
<h2 id="-">空白与注释</h2>
|
||
<p>空白（<em>whitespace</em>）有两个用途：分隔源文件中的标记和区分运算符属于前缀还是后缀，（参见 <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/doc/uid/TP40014097-CH30-XID_871" target="_blank">运算符</a>）在其他情况下则会被忽略。以下的字符会被当作空白：空格（<em>space</em>）（U+0020）、换行符（<em>line feed</em>）（U+000A）、回车符（<em>carriage return</em>）（U+000D）、水平 tab（<em>horizontal tab</em>）（U+0009）、垂直 tab（<em>vertical tab</em>）（U+000B）、换页符（<em>form feed</em>）（U+000C）以及空（<em>null</em>）（U+0000）。</p>
|
||
<p>注释（<em>comments</em>）被编译器当作空白处理。单行注释由 <code>//</code> 开始直到该行结束。多行注释由 <code>/*</code> 开始，以 <code>*/</code> 结束。可以嵌套注释，但注意注释标记必须匹配。</p>
|
||
<h2 id="-">标识符</h2>
|
||
<p>标识符（<em>identifiers</em>）可以由以下的字符开始：大写或小写的字母 <code>A</code> 到 <code>Z</code>、下划线 <code>_</code>、基本多语言面（<em>Basic Multilingual Plane</em>）中的 Unicode 非组合字符以及基本多语言面以外的非专用区（<em>Private Use Area</em>）字符。首字符之后，标识符允许使用数字和 Unicode 字符组合。</p>
|
||
<p>使用保留字（<em>reserved word</em>）作为标识符，需要在其前后增加反引号 <code>`</code>。例如，<code>class</code> 不是合法的标识符，但可以使用 <code>`class`</code>。反引号不属于标识符的一部分，<code>`x`</code> 和 <code>x</code> 表示同一标识符。</p>
|
||
<p>闭包（<em>closure</em>）中如果没有明确指定参数名称，参数将被隐式命名为 <code>$0</code>、<code>$1</code>、<code>$2</code>... 这些命名在闭包作用域内是合法的标识符。</p>
|
||
<blockquote>
|
||
<p>标识符语法</p>
|
||
<p><em>identifier</em> → <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier-head" target="_blank">identifier-head</a> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier-characters" target="_blank">identifier-characters</a> <em>opt</em></p>
|
||
<p><em>identifier</em> → ` <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier-head" target="_blank">identifier-head</a> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier-characters" target="_blank">identifier-characters</a> <em>opt</em> `</p>
|
||
<p><em>identifier</em> → <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/implicit-parameter-name" target="_blank">implicit-parameter-name</a></p>
|
||
<p><em>identifier-list</em> → <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier" target="_blank">identifier</a> | <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier" target="_blank">identifier</a> , <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier-list" target="_blank">identifier-list</a></p>
|
||
<p><em>identifier-head</em> → A 到 Z 大写或小写字母</p>
|
||
<p><em>identifier-head</em> → U+00A8, U+00AA, U+00AD, U+00AF, U+00B2–U+00B5, 或 U+00B7–U+00BA</p>
|
||
<p><em>identifier-head</em> → U+00BC–U+00BE, U+00C0–U+00D6, U+00D8–U+00F6, 或 U+00F8–U+00FF</p>
|
||
<p><em>identifier-head</em> → U+0100–U+02FF, U+0370–U+167F, U+1681–U+180D, 或 U+180F–U+1DBF</p>
|
||
<p><em>identifier-head</em> → U+1E00–U+1FFF</p>
|
||
<p><em>identifier-head</em> → U+200B–U+200D, U+202A–U+202E, U+203F–U+2040, U+2054, 或 U+2060–U+206F</p>
|
||
<p><em>identifier-head</em> → U+2070–U+20CF, U+2100–U+218F, U+2460–U+24FF, 或 U+2776–U+2793</p>
|
||
<p><em>identifier-head</em> → U+2C00–U+2DFF 或 U+2E80–U+2FFF</p>
|
||
<p><em>identifier-head</em> → U+3004–U+3007, U+3021–U+302F, U+3031–U+303F, 或 U+3040–U+D7FF</p>
|
||
<p><em>identifier-head</em> → U+F900–U+FD3D, U+FD40–U+FDCF, U+FDF0–U+FE1F, 或 U+FE30–U+FE44</p>
|
||
<p><em>identifier-head</em> → U+FE47–U+FFFD</p>
|
||
<p><em>identifier-head</em> → U+10000–U+1FFFD, U+20000–U+2FFFD, U+30000–U+3FFFD, 或 U+40000–U+4FFFD</p>
|
||
<p><em>identifier-head</em> → U+50000–U+5FFFD, U+60000–U+6FFFD, U+70000–U+7FFFD, 或 U+80000–U+8FFFD</p>
|
||
<p><em>identifier-head</em> → U+90000–U+9FFFD, U+A0000–U+AFFFD, U+B0000–U+BFFFD, 或 U+C0000–U+CFFFD</p>
|
||
<p><em>identifier-head</em> → U+D0000–U+DFFFD 或 U+E0000–U+EFFFD</p>
|
||
<p><em>identifier-character</em> → 数字 0 到 9</p>
|
||
<p><em>identifier-character</em> → U+0300–U+036F, U+1DC0–U+1DFF, U+20D0–U+20FF, or U+FE20–U+FE2F</p>
|
||
<p><em>identifier-character</em> → <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier-head" target="_blank">identifier-head</a></p>
|
||
<p><em>identifier-characters</em> → <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier-character" target="_blank">identifier-character</a> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/identifier-characters" target="_blank">identifier-characters</a> <em>opt</em></p>
|
||
<p><em>implicit-parameter-name</em> → <strong>$</strong> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/decimal-digits" target="_blank">decimal-digits</a></p>
|
||
</blockquote>
|
||
<h2 id="-">关键字</h2>
|
||
<p>被保留的关键字（<em>keywords</em>）不允许用作标识符，除非被反引号转义，参见 <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/doc/uid/TP40014097-CH30-XID_796" target="_blank">标识符</a>。</p>
|
||
<ul>
|
||
<li><p><strong>用作声明的关键字：</strong> <em>class</em>、<em>deinit</em>、<em>enum</em>、<em>extension</em>、<em>func</em>、<em>import</em>、<em>init</em>、<em>let</em>、<em>protocol</em>、<em>static</em>、<em>struct</em>、<em>subscript</em>、<em>typealias</em>、<em>var</em> </p>
|
||
</li>
|
||
<li><p><strong>用作语句的关键字：</strong> <em>break</em>、<em>case</em>、<em>continue</em>、<em>default</em>、<em>do</em>、<em>else</em>、<em>fallthrough</em>、<em>if</em>、<em>in</em>、<em>for</em>、<em>return</em>、<em>switch</em>、<em>where</em>、<em>while</em></p>
|
||
</li>
|
||
<li><p><strong>用作表达和类型的关键字：</strong> <em>as</em>、<em>dynamicType</em>、<em>is</em>、<em>new</em>、<em>super</em>、<em>self</em>、<em>Self</em>、<em>Type</em>、<em>__COLUMN__</em>、<em>__FILE__</em>、<em>__FUNCTION__</em>、<em>__LINE__</em></p>
|
||
</li>
|
||
<li><p><strong>特定上下文中被保留的关键字：</strong> <em>associativity</em>、<em>didSet</em>、<em>get</em>、<em>infix</em>、<em>inout</em>、<em>left</em>、<em>mutating</em>、<em>none</em>、<em>nonmutating</em>、<em>operator</em>、<em>override</em>、<em>postfix</em>、<em>precedence</em>、<em>prefix</em>、<em>right</em>、<em>set</em>、<em>unowned</em>、<em>unowned(safe)</em>、<em>unowned(unsafe)</em>、<em>weak</em>、<em>willSet</em>，这些关键字在特定上下文之外可以被用于标识符。</p>
|
||
</li>
|
||
</ul>
|
||
<h2 id="-">字面量</h2>
|
||
<p>字面值表示整型、浮点型数字或文本类型的值，举例如下：</p>
|
||
<pre><code>42 // 整型字面量
|
||
3.14159 // 浮点型字面量
|
||
"Hello, world!" // 文本型字面量
|
||
</code></pre><blockquote>
|
||
<p>字面量语法</p>
|
||
<p><em>literal</em> → <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/integer-literal" target="_blank">integer-literal</a> | <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/floating-point-literal" target="_blank">floating-point-literal</a> | <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/string-literal" target="_blank">string-literal</a></p>
|
||
</blockquote>
|
||
<h3 id="-">整型字面量</h3>
|
||
<p>整型字面量（<em>integer literals</em>）表示未指定精度整型数的值。整型字面量默认用十进制表示，可以加前缀来指定其他的进制，二进制字面量加 <code>0b</code>，八进制字面量加 <code>0o</code>，十六进制字面量加 <code>0x</code>。</p>
|
||
<p>十进制字面量包含数字 <code>0</code> 至 <code>9</code>。二进制字面量只包含 <code>0</code> 或 <code>1</code>，八进制字面量包含数字 <code>0</code> 至 <code>7</code>，十六进制字面量包含数字 <code>0</code> 至 <code>9</code> 以及字母 <code>A</code> 至 <code>F</code> （大小写均可）。</p>
|
||
<p>负整数的字面量在数字前加减号 <code>-</code>，比如 <code>-42</code>。</p>
|
||
<p>允许使用下划线 <code>_</code> 来增加数字的可读性，下划线不会影响字面量的值。整型字面量也可以在数字前加 <code>0</code>，同样不会影响字面量的值。</p>
|
||
<pre><code>1000_000 // 等于 1000000
|
||
005 // 等于 5
|
||
</code></pre><p>除非特殊指定，整型字面量的默认类型为 Swift 标准库类型中的 <code>Int</code>。Swift 标准库还定义了其他不同长度以及是否带符号的整数类型，请参考 <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/TheBasics.html#//apple_ref/doc/uid/TP40014097-CH5-XID_411" target="_blank">整数类型</a>。</p>
|
||
<blockquote>
|
||
<p>整型字面量语法</p>
|
||
<p><em>integer-literal</em> → <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/binary-literal" target="_blank">binary-literal</a></p>
|
||
<p><em>integer-literal</em> → <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/octal-literal" target="_blank">octal-literal</a></p>
|
||
<p><em>integer-literal</em> → <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/decimal-literal" target="_blank">decimal-literal</a></p>
|
||
<p><em>integer-literal</em> → <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-literal" target="_blank">hexadecimal-literal</a></p>
|
||
<p><em>binary-literal</em> → <strong>0b</strong> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/binary-digit" target="_blank">binary-digit</a> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/binary-literal-characters" target="_blank">binary-literal-characters</a> <em>opt</em></p>
|
||
<p><em>binary-digit</em> → 数字 0 或 1</p>
|
||
<p><em>binary-literal-character</em> → <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/binary-digit" target="_blank">binary-digit</a> | _</p>
|
||
<p><em>binary-literal-characters</em> → <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/binary-literal-character" target="_blank">binary-literal-character</a> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/binary-literal-characters" target="_blank">binary-literal-characters</a> <em>opt</em></p>
|
||
<p><em>octal-literal</em> → <strong>0o</strong> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/octal-digit" target="_blank">octal-digit</a> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/octal-literal-characters" target="_blank">octal-literal-characters</a> <em>opt</em></p>
|
||
<p><em>octal-digit</em> → 数字 0 至 7</p>
|
||
<p><em>octal-literal-character</em> → <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/octal-digit" target="_blank">octal-digit</a> | _</p>
|
||
<p><em>octal-literal-characters</em> → <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/octal-literal-character" target="_blank">octal-literal-character</a> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/octal-literal-characters" target="_blank">octal-literal-characters</a> <em>opt</em></p>
|
||
<p><em>decimal-literal</em> → <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/decimal-digit" target="_blank">decimal-digit</a> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/decimal-literal-characters" target="_blank">decimal-literal-characters</a> <em>opt</em></p>
|
||
<p><em>decimal-digit</em> → 数字 0 至 9</p>
|
||
<p><em>decimal-digits</em> → <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/decimal-digit" target="_blank">decimal-digit</a> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/decimal-digits" target="_blank">decimal-digits</a> <em>opt</em></p>
|
||
<p><em>decimal-literal-character</em> → <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/decimal-digit" target="_blank">decimal-digit</a> | _</p>
|
||
<p><em>decimal-literal-characters</em> → <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/decimal-literal-character" target="_blank">decimal-literal-character</a> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/decimal-literal-characters" target="_blank">decimal-literal-characters</a> <em>opt</em></p>
|
||
<p><em>hexadecimal-literal</em> → <strong>0x</strong> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-digit" target="_blank">hexadecimal-digit</a> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-literal-characters" target="_blank">hexadecimal-literal-characters</a> <em>opt</em></p>
|
||
<p><em>hexadecimal-digit</em> → 数字 0 到 9, a 到 f, 或 A 到 F</p>
|
||
<p><em>hexadecimal-literal-character</em> → <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-digit" target="_blank">hexadecimal-digit</a> | _</p>
|
||
<p><em>hexadecimal-literal-characters</em> → <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-literal-character" target="_blank">hexadecimal-literal-character</a> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-literal-characters" target="_blank">hexadecimal-literal-characters</a> <em>opt</em></p>
|
||
</blockquote>
|
||
<h3 id="-">浮点型字面量</h3>
|
||
<p>浮点型字面量（<em>floating-point literals</em>）表示未指定精度浮点数的值。</p>
|
||
<p>浮点型字面量默认用十进制表示（无前缀），也可以用十六进制表示（加前缀 <code>0x</code>）。</p>
|
||
<p>十进制浮点型字面量（<em>decimal floating-point literals</em>）由十进制数字串后跟小数部分或指数部分（或两者皆有）组成。十进制小数部分由小数点 <code>.</code> 后跟十进制数字串组成。指数部分由大写或小写字母 <code>e</code> 后跟十进制数字串组成，这串数字表示 <code>e</code> 之前的数量乘以 10 的几次方。例如：<code>1.25e2</code> 表示 <code>1.25 ⨉ 10^2</code>，也就是 <code>125.0</code>；同样，<code>1.25e－2</code> 表示 <code>1.25 ⨉ 10^－2</code>，也就是 <code>0.0125</code>。</p>
|
||
<p>十六进制浮点型字面量（<em>hexadecimal floating-point literals</em>）由前缀 <code>0x</code> 后跟可选的十六进制小数部分以及十六进制指数部分组成。十六进制小数部分由小数点后跟十六进制数字串组成。指数部分由大写或小写字母 <code>p</code> 后跟十进制数字串组成，这串数字表示 <code>p</code> 之前的数量乘以 2 的几次方。例如：<code>0xFp2</code> 表示 <code>15 ⨉ 2^2</code>，也就是 <code>60</code>；同样，<code>0xFp-2</code> 表示 <code>15 ⨉ 2^-2</code>，也就是 <code>3.75</code>。</p>
|
||
<p>与整型字面量不同，负的浮点型字面量由一元运算符减号 <code>-</code> 和浮点型字面量组成，例如 <code>-42.0</code>。这代表一个表达式，而不是一个浮点整型字面量。</p>
|
||
<p>允许使用下划线 <code>_</code> 来增强可读性，下划线不会影响字面量的值。浮点型字面量也可以在数字前加 <code>0</code>，同样不会影响字面量的值。</p>
|
||
<pre><code>10_000.56 // 等于 10000.56
|
||
005000.76 // 等于 5000.76
|
||
</code></pre><p>除非特殊指定，浮点型字面量的默认类型为 Swift 标准库类型中的 <code>Double</code>，表示64位浮点数。Swift 标准库也定义 <code>Float</code> 类型，表示32位浮点数。</p>
|
||
<blockquote>
|
||
<p>浮点型字面量语法</p>
|
||
<p><em>floating-point-literal</em> → <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/decimal-literal" target="_blank">decimal-literal</a> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/decimal-fraction" target="_blank">decimal-fraction</a> <em>opt</em> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/decimal-exponent" target="_blank">decimal-exponent</a> <em>opt</em></p>
|
||
<p><em>floating-point-literal</em> → <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-literal" target="_blank">hexadecimal-literal</a> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-fraction" target="_blank">hexadecimal-fraction</a> <em>opt</em> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-exponent" target="_blank">hexadecimal-exponent</a></p>
|
||
<p><em>decimal-fraction</em> → . <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/decimal-literal" target="_blank">decimal-literal</a></p>
|
||
<p><em>decimal-exponent</em> → <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/floating-point-e" target="_blank">floating-point-e</a> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/sign" target="_blank">sign</a> <em>opt</em> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/decimal-literal" target="_blank">decimal-literal</a></p>
|
||
<p><em>hexadecimal-fraction</em> → . <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-literal" target="_blank">hexadecimal-literal</a> <em>opt</em></p>
|
||
<p><em>hexadecimal-exponent</em> → <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/floating-point-p" target="_blank">floating-point-p</a> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/sign" target="_blank">sign</a> <em>opt</em> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-literal" target="_blank">hexadecimal-literal</a></p>
|
||
<p><em>floating-point-e</em> → <strong>e</strong> | <strong>E</strong></p>
|
||
<p><em>floating-point-p</em> → <strong>p</strong> | <strong>P</strong></p>
|
||
<p><em>sign</em> → <strong>+</strong> | <strong>-</strong></p>
|
||
</blockquote>
|
||
<h3 id="-">文本型字面量</h3>
|
||
<p>文本型字面量（<em>string literal</em>）由双引号中的字符串组成，形式如下：</p>
|
||
<pre><code>"characters"
|
||
</code></pre><p>文本型字面量中不能包含未转义的双引号 <code>"</code>、未转义的反斜线<code>\</code>、回车符（<em>carriage return</em>）或换行符（<em>line feed</em>）。</p>
|
||
<p>可以在文本型字面量中使用的转义特殊符号如下：</p>
|
||
<ul>
|
||
<li>空字符（Null Character）<code>\0</code></li>
|
||
<li>反斜线（Backslash）<code>\\</code></li>
|
||
<li>水平 Tab （Horizontal Tab）<code>\t</code></li>
|
||
<li>换行符（Line Feed）<code>\n</code></li>
|
||
<li>回车符（Carriage Return）<code>\r</code></li>
|
||
<li>双引号（Double Quote）<code>\"</code></li>
|
||
<li>单引号（Single Quote）<code>\'</code></li>
|
||
</ul>
|
||
<p>字符也可以用以下方式表示：</p>
|
||
<ul>
|
||
<li><code>\x</code> 后跟两位十六进制数字</li>
|
||
<li><code>\u</code> 后跟四位十六进制数字</li>
|
||
<li><code>\U</code> 后跟八位十六进制数字</li>
|
||
</ul>
|
||
<p>后跟的数字表示一个 Unicode 码点。</p>
|
||
<p>文本型字面量允许在反斜线小括号 <code>\()</code> 中插入表达式的值。插入表达式（<em>interpolated expression</em>）不能包含未转义的双引号 <code>"</code>、反斜线 <code>\</code>、回车符或者换行符。表达式值的类型必须在 <em>String</em> 类中有对应的初始化方法。</p>
|
||
<p>例如，以下所有文本型字面量的值相同：</p>
|
||
<pre><code>"1 2 3"
|
||
"1 2 \(3)"
|
||
"1 2 \(1 + 2)"
|
||
var x = 3; "1 2 \(x)"
|
||
</code></pre><p>文本型字面量的默认类型为 <code>String</code>。组成字符串的字符类型为 <code>Character</code>。更多有关 <code>String</code> 和 <code>Character</code> 的信息请参照 <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/StringsAndCharacters.html#//apple_ref/doc/uid/TP40014097-CH7-XID_368" target="_blank">字符串和字符</a>。</p>
|
||
<blockquote>
|
||
<p>文本型字面量语法</p>
|
||
<p><em>string-literal</em> → <strong>"</strong> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/quoted-text" target="_blank">quoted-text</a> <strong>"</strong></p>
|
||
<p><em>quoted-text</em> → <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/quoted-text-item" target="_blank">quoted-text-item</a> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/quoted-text" target="_blank">quoted-text</a> <em>opt</em></p>
|
||
<p><em>quoted-text-item</em> → <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/escaped-character" target="_blank">escaped-character</a></p>
|
||
<p><em>quoted-text-item</em> → <strong>(</strong> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Expressions.html#//apple_ref/swift/grammar/expression" target="_blank">expression</a> <strong>)</strong></p>
|
||
<p><em>quoted-text-item</em> → 除 <code>"</code>、<code>\</code>、<code>U+000A</code> 或 <code>U+000D</code> 以外的任何 Unicode 扩展字符集</p>
|
||
<p><em>escaped-character</em> → <strong>\0</strong> | <strong>\</strong> | <strong>\t</strong> | <strong>\n</strong> | <strong>\r</strong> | <strong>\"</strong> | <strong>\'</strong></p>
|
||
<p><em>escaped-character</em> → <strong>\x</strong> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-digit" target="_blank">hexadecimal-digit</a> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-digit" target="_blank">hexadecimal-digit</a></p>
|
||
<p><em>escaped-character</em> → <strong>\u</strong> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-digit" target="_blank">hexadecimal-digit</a> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-digit" target="_blank">hexadecimal-digit</a> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-digit" target="_blank">hexadecimal-digit</a> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-digit" target="_blank">hexadecimal-digit</a></p>
|
||
<p><em>escaped-character</em> → <strong>\U</strong> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-digit" target="_blank">hexadecimal-digit</a> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-digit" target="_blank">hexadecimal-digit</a> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-digit" target="_blank">hexadecimal-digit</a> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-digit" target="_blank">hexadecimal-digit</a> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-digit" target="_blank">hexadecimal-digit</a> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-digit" target="_blank">hexadecimal-digit</a> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-digit" target="_blank">hexadecimal-digit</a> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/hexadecimal-digit" target="_blank">hexadecimal-digit</a></p>
|
||
</blockquote>
|
||
<h2 id="-">运算符</h2>
|
||
<p>Swift 标准库定义了许多可供使用的运算符，其中大部分在 <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/BasicOperators.html#//apple_ref/doc/uid/TP40014097-CH6-XID_70" target="_blank">基础运算符</a> 和 <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/AdvancedOperators.html#//apple_ref/doc/uid/TP40014097-CH27-XID_28" target="_blank">高级运算符</a> 中进行了阐述。这里将描述哪些字符能用作运算符。</p>
|
||
<p>运算符由一个或多个以下字符组成：
|
||
<code>/</code>、<code>=</code>、<code>-</code>、<code>+</code>、<code>!</code>、<code>*</code>、<code>%</code>、<code><</code>、<code>></code>、<code>&</code>、<code>|</code>、<code>^</code>、<code>~</code>、<code>.</code>。也就是说，标记 <code>=</code>, <code>-></code>、<code>//</code>、<code>/*</code>、<code>*/</code>、<code>.</code> 以及一元前缀运算符 <code>&</code> 属于保留字，这些标记不能被重写或用于自定义运算符。</p>
|
||
<p>运算符两侧的空白被用来区分该运算符是否为前缀运算符（<em>prefix operator</em>）、后缀运算符（<em>postfix operator</em>）或二元运算符（<em>binary operator</em>）。规则总结如下：</p>
|
||
<ul>
|
||
<li><p>如果运算符两侧都有空白或两侧都无空白，将被看作二元运算符。例如：<code>a+b</code> 和 <code>a + b</code> 中的运算符 <code>+</code> 被看作二元运算符。</p>
|
||
</li>
|
||
<li><p>如果运算符只有左侧空白，将被看作前缀一元运算符。例如 <code>a ++b</code> 中的 <code>++</code> 被看作前缀一元运算符。</p>
|
||
</li>
|
||
<li><p>如果运算符只有右侧空白，将被看作后缀一元运算符。例如 <code>a++ b</code> 中的 <code>++</code> 被看作后缀一元运算符。</p>
|
||
</li>
|
||
<li><p>如果运算符左侧没有空白并紧跟 <code>.</code>，将被看作后缀一元运算符。例如 <code>a++.b</code> 中的 <code>++</code> 被看作后缀一元运算符（同理， <code>a++ . b</code> 中的 <code>++</code> 是后缀一元运算符而 <code>a ++ .b</code> 中的 <code>++</code> 不是）.</p>
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||
</li>
|
||
</ul>
|
||
<p>鉴于这些规则，运算符前的字符 <code>(</code>、<code>[</code> 和 <code>{</code> ；运算符后的字符 <code>)</code>、<code>]</code> 和 <code>}</code> 以及字符 <code>,</code>、<code>;</code> 和 <code>:</code> 都将用于空白检测。</p>
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||
<p>以上规则需注意一点，如果运算符 <code>!</code> 或 <code>?</code> 左侧没有空白，则不管右侧是否有空白都将被看作后缀运算符。如果将 <code>?</code> 用作可选类型（<em>optional type</em>）修饰，左侧必须无空白。如果用于条件运算符 <code>? :</code>，必须两侧都有空白。 </p>
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||
<p>在特定构成中 ，以 <code><</code> 或 <code>></code> 开头的运算符会被分离成两个或多个标记，剩余部分以同样的方式会被再次分离。因此，在 <code>Dictionary<String, Array<Int>></code> 中没有必要添加空白来消除闭合字符 <code>></code> 的歧义。在这个例子中， 闭合字符 <code>></code> 被看作单字符标记，而不会被误解为移位运算符 <code>>></code>。</p>
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||
<p>要学习如何自定义新的运算符，请参考 <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/AdvancedOperators.html#//apple_ref/doc/uid/TP40014097-CH27-XID_48" target="_blank">自定义操作符</a> 和 <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/doc/uid/TP40014097-CH34-XID_644" target="_blank">运算符声明</a>。学习如何重写现有运算符，请参考 <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/AdvancedOperators.html#//apple_ref/doc/uid/TP40014097-CH27-XID_43" target="_blank">运算符方法</a>。</p>
|
||
<blockquote>
|
||
<p>运算符语法</p>
|
||
<p><em>operator</em> → <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/operator-character" target="_blank">operator-character</a> <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/operator" target="_blank">operator</a> <em>opt</em></p>
|
||
<p><em>operator-character</em> → <strong>/</strong> | <strong>=</strong> | <strong>-</strong> | <strong>+</strong> | <strong>!</strong> | <strong>*</strong> | <strong>%</strong> | <strong><</strong> | <strong>></strong> | <strong>&</strong> | <strong>|</strong> | <strong>^</strong> | <strong>~</strong> | <strong>.</strong></p>
|
||
<p><em>binary-operator</em> → <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/operator" target="_blank">operator</a></p>
|
||
<p><em>prefix-operator</em> → <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/operator" target="_blank">operator</a></p>
|
||
<p><em>postfix-operator</em> → <a href="https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html#//apple_ref/swift/grammar/operator" target="_blank">operator</a></p>
|
||
</blockquote>
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