fix 2.21 protocols
This commit is contained in:
stanzhai
@ -1,6 +1,5 @@
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> 翻译：geek5nan
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> 校对：dabing1022
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> 翻译：geek5nan
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> 校对：dabing1022
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# 协议
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-----------------
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@ -30,22 +29,28 @@
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`协议`的定义与类，结构体，枚举的定义非常相似，如下所示：
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protocol SomeProtocol {
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// 协议内容
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}
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```swift
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protocol SomeProtocol {
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// 协议内容
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}
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```
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在类，结构体，枚举的名称后加上`协议名称`，中间以冒号`:`分隔即可实现协议；实现多个协议时，各协议之间用逗号`,`分隔，如下所示：
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struct SomeStructure: FirstProtocol, AnotherProtocol {
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// 结构体内容
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}
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```swift
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struct SomeStructure: FirstProtocol, AnotherProtocol {
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// 结构体内容
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}
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```
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当某个类含有父类的同时并实现了协议，应当把父类放在所有的协议之前，如下所示：
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class SomeClass: SomeSuperClass, FirstProtocol, AnotherProtocol {
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// 类的内容
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}
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```swift
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class SomeClass: SomeSuperClass, FirstProtocol, AnotherProtocol {
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// 类的内容
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}
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```
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<a name="property_requirements"></a>
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## 属性要求
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@ -54,46 +59,54 @@
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通常前置`var`关键字将属性声明为变量。在属性声明后写上`{ get set }`表示属性为可读写的。`{ get }`用来表示属性为可读的。即使你为可读的属性实现了`setter`方法，它也不会出错。
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protocol SomeProtocol {
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var musBeSettable : Int { get set }
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var doesNotNeedToBeSettable: Int { get }
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}
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```swift
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protocol SomeProtocol {
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var musBeSettable : Int { get set }
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var doesNotNeedToBeSettable: Int { get }
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}
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```
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用类来实现协议时，使用`class`关键字来表示该属性为类成员；用结构体或枚举实现协议时，则使用`static`关键字来表示：
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protocol AnotherProtocol {
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class var someTypeProperty: Int { get set }
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}
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```swift
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protocol AnotherProtocol {
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class var someTypeProperty: Int { get set }
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}
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protocol FullyNamed {
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var fullName: String { get }
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}
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protocol FullyNamed {
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var fullName: String { get }
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}
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```
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`FullyNamed`协议含有`fullName`属性。因此其`遵循者`必须含有一个名为`fullName`，类型为`String`的可读属性。
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struct Person: FullyNamed{
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var fullName: String
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}
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let john = Person(fullName: "John Appleseed")
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//john.fullName 为 "John Appleseed"
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```swift
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struct Person: FullyNamed{
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var fullName: String
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}
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let john = Person(fullName: "John Appleseed")
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//john.fullName 为 "John Appleseed"
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```
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`Person`结构体含有一个名为`fullName`的`存储型属性`，完整的`遵循`了协议。(*若协议未被完整遵循，编译时则会报错*)。
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如下所示，`Startship`类`遵循`了`FullyNamed`协议：
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class Starship: FullyNamed {
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var prefix: String?
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var name: String
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init(name: String, prefix: String? = nil ) {
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self.anme = name
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self.prefix = prefix
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}
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var fullName: String {
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return (prefix ? prefix ! + " " : " ") + name
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}
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```swift
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class Starship: FullyNamed {
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var prefix: String?
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var name: String
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init(name: String, prefix: String? = nil ) {
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self.anme = name
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self.prefix = prefix
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}
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var ncc1701 = Starship(name: "Enterprise", prefix: "USS")
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// ncc1701.fullName == "USS Enterprise"
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var fullName: String {
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return (prefix ? prefix ! + " " : " ") + name
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}
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}
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var ncc1701 = Starship(name: "Enterprise", prefix: "USS")
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// ncc1701.fullName == "USS Enterprise"
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```
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`Starship`类将`fullName`实现为可读的`计算型属性`。它的每一个实例都有一个名为`name`的必备属性和一个名为`prefix`的可选属性。 当`prefix`存在时，将`prefix`插入到`name`之前来为`Starship`构建`fullName`。
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@ -102,39 +115,42 @@
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`协议`能够要求其`遵循者`必备某些特定的`实例方法`和`类方法`。协议方法的声明与普通方法声明相似，但它不需要`方法`内容。
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> 注意：
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>
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> 注意：
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协议方法支持`变长参数(variadic parameter)`，不支持`默认参数(default parameter)`。
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前置`class`关键字表示协议中的成员为`类成员`；当协议用于被`枚举`或`结构体`遵循时，则使用`static`关键字。如下所示：
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protocol SomeProtocol {
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class func someTypeMethod()
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}
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```swift
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protocol SomeProtocol {
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class func someTypeMethod()
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}
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protocol RandomNumberGenerator {
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func random() -> Double
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}
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protocol RandomNumberGenerator {
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func random() -> Double
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}
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```
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`RandomNumberGenerator`协议要求其`遵循者`必须拥有一个名为`random`， 返回值类型为`Double`的实例方法。(我们假设随机数在[0，1]区间内)。
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`LinearCongruentialGenerator`类`遵循`了`RandomNumberGenerator`协议，并提供了一个叫做*线性同余生成器(linear congruential generator)*的伪随机数算法。
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class LinearCongruentialGenerator: RandomNumberGenerator {
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var lastRandom = 42.0
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let m = 139968.0
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let a = 3877.0
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let c = 29573.0
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func random() -> Double {
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lastRandom = ((lastRandom * a + c) % m)
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return lastRandom / m
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}
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```swift
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class LinearCongruentialGenerator: RandomNumberGenerator {
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var lastRandom = 42.0
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let m = 139968.0
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let a = 3877.0
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let c = 29573.0
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func random() -> Double {
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lastRandom = ((lastRandom * a + c) % m)
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return lastRandom / m
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}
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let generator = LinearCongruentialGenerator()
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println("Here's a random number: \(generator.random())")
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// 输出 : "Here's a random number: 0.37464991998171"
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println("And another one: \(generator.random())")
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// 输出 : "And another one: 0.729023776863283"
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}
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let generator = LinearCongruentialGenerator()
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println("Here's a random number: \(generator.random())")
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// 输出 : "Here's a random number: 0.37464991998171"
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println("And another one: \(generator.random())")
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// 输出 : "And another one: 0.729023776863283"
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```
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<a name="mutating_method_requirements"></a>
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## 突变方法要求
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@ -143,34 +159,37 @@
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(*译者注：类中的成员为`引用类型(Reference Type)`，可以方便的修改实例及其属性的值而无需改变类型；而`结构体`和`枚举`中的成员均为`值类型(Value Type)`，修改变量的值就相当于修改变量的类型，而`Swift`默认不允许修改类型，因此需要前置`mutating`关键字用来表示该`函数`中能够修改类型*)
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> 注意：
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>
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> 注意：
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用`class`实现协议中的`mutating`方法时，不用写`mutating`关键字；用`结构体`，`枚举`实现协议中的`mutating`方法时，必须写`mutating`关键字。
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如下所示，`Togglable`协议含有`toggle`函数。根据函数名称推测，`toggle`可能用于**切换或恢复**某个属性的状态。`mutating`关键字表示它为`突变方法`：
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protocol Togglable {
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mutating func toggle()
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}
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```swift
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protocol Togglable {
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mutating func toggle()
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}
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```
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当使用`枚举`或`结构体`来实现`Togglabl`协议时，必须在`toggle`方法前加上`mutating`关键字。
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如下所示，`OnOffSwitch`枚举`遵循`了`Togglable`协议，`On`，`Off`两个成员用于表示当前状态
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enum OnOffSwitch: Togglable {
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case Off, On
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mutating func toggle() {
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switch self {
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case Off:
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self = On
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case On:
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self = Off
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}
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```swift
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enum OnOffSwitch: Togglable {
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case Off, On
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mutating func toggle() {
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switch self {
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case Off:
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self = On
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case On:
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self = Off
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}
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}
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var lightSwitch = OnOffSwitch.Off
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lightSwitch.toggle()
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//lightSwitch 现在的值为 .On
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}
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var lightSwitch = OnOffSwitch.Off
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lightSwitch.toggle()
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//lightSwitch 现在的值为 .On
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```
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<a name="protocols_as_types"></a>
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## 协议类型
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@ -183,25 +202,26 @@
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* 作为常量，变量，属性的类型
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* 作为数组，字典或其他容器中的元素类型
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> 注意：
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>
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> 注意：
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协议类型应与其他类型(Int，Double，String)的写法相同，使用驼峰式
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class Dice {
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let sides: Int
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let generator: RandomNumberGenerator
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init(sides: Int, generator: RandomNumberGenerator) {
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self.sides = sides
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self.generator = generator
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}
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func roll() -> Int {
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return Int(generator.random() * Double(sides)) +1
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}
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```swift
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class Dice {
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let sides: Int
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let generator: RandomNumberGenerator
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init(sides: Int, generator: RandomNumberGenerator) {
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self.sides = sides
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self.generator = generator
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}
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func roll() -> Int {
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return Int(generator.random() * Double(sides)) +1
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}
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}
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```
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这里定义了一个名为 `Dice`的类，用来代表桌游中的N个面的骰子。
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`Dice`含有`sides`和`generator`两个属性，前者用来表示骰子有几个面，后者为骰子提供一个随机数生成器。由于后者为`RandomNumberGenerator`的协议类型。所以它能够被赋值为任意`遵循`该协议的类型。
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`Dice`含有`sides`和`generator`两个属性，前者用来表示骰子有几个面，后者为骰子提供一个随机数生成器。由于后者为`RandomNumberGenerator`的协议类型。所以它能够被赋值为任意`遵循`该协议的类型。
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此外，使用`构造器(init)`来代替之前版本中的`setup`操作。构造器中含有一个名为`generator`，类型为`RandomNumberGenerator`的形参，使得它可以接收任意遵循`RandomNumberGenerator`协议的类型。
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@ -209,16 +229,18 @@
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如下所示，`LinearCongruentialGenerator`的实例作为随机数生成器传入`Dice`的`构造器`
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var d6 = Dice(sides: 6,generator: LinearCongruentialGenerator())
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for _ in 1...5 {
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println("Random dice roll is \(d6.roll())")
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}
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//输出结果
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//Random dice roll is 3
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//Random dice roll is 5
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//Random dice roll is 4
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//Random dice roll is 5
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//Random dice roll is 4
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```swift
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var d6 = Dice(sides: 6,generator: LinearCongruentialGenerator())
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for _ in 1...5 {
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println("Random dice roll is \(d6.roll())")
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}
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//输出结果
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//Random dice roll is 3
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//Random dice roll is 5
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//Random dice roll is 4
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//Random dice roll is 5
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//Random dice roll is 4
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```
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<a name="delegation"></a>
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## 委托(代理)模式
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@ -231,55 +253,59 @@
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下文是两个基于骰子游戏的协议：
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protocol DiceGame {
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var dice: Dice { get }
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func play()
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}
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protocol DiceGameDelegate {
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func gameDidStart(game: DiceGame)
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func game(game: DiceGame, didStartNewTurnWithDiceRoll diceRoll:Int)
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func gameDidEnd(game: DiceGame)
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}
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```swift
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protocol DiceGame {
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var dice: Dice { get }
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func play()
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}
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protocol DiceGameDelegate {
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func gameDidStart(game: DiceGame)
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func game(game: DiceGame, didStartNewTurnWithDiceRoll diceRoll:Int)
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func gameDidEnd(game: DiceGame)
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}
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```
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`DiceGame`协议可以在任意含有骰子的游戏中实现，`DiceGameDelegate`协议可以用来追踪`DiceGame`的游戏过程。
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如下所示，`SnakesAndLadders`是`Snakes and Ladders`(译者注：[控制流](05_Control_Flow.html)章节有该游戏的详细介绍)游戏的新版本。新版本使用`Dice`作为骰子，并且实现了`DiceGame`和`DiceGameDelegate`协议
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class SnakesAndLadders: DiceGame {
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let finalSquare = 25
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let dic = Dice(sides: 6, generator: LinearCongruentialGenerator())
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var square = 0
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var board: Int[]
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init() {
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board = Int[](count: finalSquare + 1, repeatedValue: 0)
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board[03] = +08; board[06] = +11; borad[09] = +09; board[10] = +02
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borad[14] = -10; board[19] = -11; borad[22] = -02; board[24] = -08
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}
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var delegate: DiceGameDelegate?
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func play() {
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square = 0
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delegate?.gameDidStart(self)
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gameLoop: while square != finalSquare {
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let diceRoll = dice.roll()
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delegate?.game(self,didStartNewTurnWithDiceRoll: diceRoll)
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switch square + diceRoll {
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case finalSquare:
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break gameLoop
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case let newSquare where newSquare > finalSquare:
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continue gameLoop
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default:
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square += diceRoll
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square += board[square]
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}
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}
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delegate?.gameDIdEnd(self)
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}
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```swift
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class SnakesAndLadders: DiceGame {
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let finalSquare = 25
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let dic = Dice(sides: 6, generator: LinearCongruentialGenerator())
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var square = 0
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var board: Int[]
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init() {
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board = Int[](count: finalSquare + 1, repeatedValue: 0)
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board[03] = +08; board[06] = +11; borad[09] = +09; board[10] = +02
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borad[14] = -10; board[19] = -11; borad[22] = -02; board[24] = -08
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}
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var delegate: DiceGameDelegate?
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func play() {
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square = 0
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delegate?.gameDidStart(self)
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gameLoop: while square != finalSquare {
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let diceRoll = dice.roll()
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delegate?.game(self,didStartNewTurnWithDiceRoll: diceRoll)
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switch square + diceRoll {
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case finalSquare:
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break gameLoop
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case let newSquare where newSquare > finalSquare:
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continue gameLoop
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default:
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square += diceRoll
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square += board[square]
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}
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}
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delegate?.gameDIdEnd(self)
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}
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}
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```
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游戏的`初始化设置(setup)`被`SnakesAndLadders`类的`构造器(initializer)`实现。所有的游戏逻辑被转移到了`play`方法中。
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> 注意：
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>
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> 注意：
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因为`delegate`并不是该游戏的必备条件，`delegate`被定义为遵循`DiceGameDelegate`协议的可选属性
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`DicegameDelegate`协议提供了三个方法用来追踪游戏过程。被放置于游戏的逻辑中，即`play()`方法内。分别在游戏开始时，新一轮开始时，游戏结束时被调用。
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@ -288,23 +314,25 @@
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如下所示，`DiceGameTracker`遵循了`DiceGameDelegate`协议
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class DiceGameTracker: DiceGameDelegate {
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var numberOfTurns = 0
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func gameDidStart(game: DiceGame) {
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numberOfTurns = 0
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if game is SnakesAndLadders {
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println("Started a new game of Snakes and Ladders")
|
||||
}
|
||||
println("The game is using a \(game.dice.sides)-sided dice")
|
||||
}
|
||||
func game(game: DiceGame, didStartNewTurnWithDiceRoll diceRoll: Int) {
|
||||
++numberOfTurns
|
||||
println("Rolled a \(diceRoll)")
|
||||
}
|
||||
func gameDidEnd(game: DiceGame) {
|
||||
println("The game lasted for \(numberOfTurns) turns")
|
||||
}
|
||||
}
|
||||
```swift
|
||||
class DiceGameTracker: DiceGameDelegate {
|
||||
var numberOfTurns = 0
|
||||
func gameDidStart(game: DiceGame) {
|
||||
numberOfTurns = 0
|
||||
if game is SnakesAndLadders {
|
||||
println("Started a new game of Snakes and Ladders")
|
||||
}
|
||||
println("The game is using a \(game.dice.sides)-sided dice")
|
||||
}
|
||||
func game(game: DiceGame, didStartNewTurnWithDiceRoll diceRoll: Int) {
|
||||
++numberOfTurns
|
||||
println("Rolled a \(diceRoll)")
|
||||
}
|
||||
func gameDidEnd(game: DiceGame) {
|
||||
println("The game lasted for \(numberOfTurns) turns")
|
||||
}
|
||||
}
|
||||
```
|
||||
|
||||
`DiceGameTracker`实现了`DiceGameDelegate`协议的方法要求，用来记录游戏已经进行的轮数。 当游戏开始时，`numberOfTurns`属性被赋值为0；在每新一轮中递加；游戏结束后，输出打印游戏的总轮数。
|
||||
|
||||
@ -312,79 +340,91 @@
|
||||
|
||||
`DiceGameTracker`的运行情况，如下所示：
|
||||
|
||||
“let tracker = DiceGameTracker()
|
||||
let game = SnakesAndLadders()
|
||||
game.delegate = tracker
|
||||
game.play()
|
||||
// Started a new game of Snakes and Ladders
|
||||
// The game is using a 6-sided dice
|
||||
// Rolled a 3
|
||||
// Rolled a 5
|
||||
// Rolled a 4
|
||||
// Rolled a 5
|
||||
// The game lasted for 4 turns”
|
||||
```swift
|
||||
“let tracker = DiceGameTracker()
|
||||
let game = SnakesAndLadders()
|
||||
game.delegate = tracker
|
||||
game.play()
|
||||
// Started a new game of Snakes and Ladders
|
||||
// The game is using a 6-sided dice
|
||||
// Rolled a 3
|
||||
// Rolled a 5
|
||||
// Rolled a 4
|
||||
// Rolled a 5
|
||||
// The game lasted for 4 turns”
|
||||
```
|
||||
|
||||
<a name="adding_protocol_conformance_with_an_extension"></a>
|
||||
## 在扩展中添加协议成员
|
||||
|
||||
即便无法修改源代码，依然可以通过`扩展(Extension)`来扩充已存在类型(*译者注： 类，结构体，枚举等*)。`扩展`可以为已存在的类型添加`属性`，`方法`，`下标`，`协议`等成员。详情请在[扩展](20_Extensions.html)章节中查看。
|
||||
|
||||
> 注意：
|
||||
>
|
||||
> 注意：
|
||||
通过`扩展`为已存在的类型`遵循`协议时，该类型的所有实例也会随之添加协议中的方法
|
||||
|
||||
`TextRepresentable`协议含有一个`asText`，如下所示：
|
||||
|
||||
protocol TextRepresentable {
|
||||
func asText() -> String
|
||||
}
|
||||
```swift
|
||||
protocol TextRepresentable {
|
||||
func asText() -> String
|
||||
}
|
||||
```
|
||||
|
||||
通过`扩展`为上一节中提到的`Dice`类遵循`TextRepresentable`协议
|
||||
|
||||
extension Dice: TextRepresentable {
|
||||
cun asText() -> String {
|
||||
return "A \(sides)-sided dice"
|
||||
}
|
||||
```swift
|
||||
extension Dice: TextRepresentable {
|
||||
cun asText() -> String {
|
||||
return "A \(sides)-sided dice"
|
||||
}
|
||||
}
|
||||
```
|
||||
|
||||
从现在起，`Dice`类型的实例可被当作`TextRepresentable`类型：
|
||||
|
||||
let d12 = Dice(sides: 12,generator: LinearCongruentialGenerator())
|
||||
println(d12.asText())
|
||||
// 输出 "A 12-sided dice"
|
||||
```swift
|
||||
let d12 = Dice(sides: 12,generator: LinearCongruentialGenerator())
|
||||
println(d12.asText())
|
||||
// 输出 "A 12-sided dice"
|
||||
```
|
||||
|
||||
`SnakesAndLadders`类也可以通过`扩展`的方式来遵循协议：
|
||||
|
||||
extension SnakeAndLadders: TextRepresentable {
|
||||
func asText() -> String {
|
||||
return "A game of Snakes and Ladders with \(finalSquare) squares"
|
||||
}
|
||||
```swift
|
||||
extension SnakeAndLadders: TextRepresentable {
|
||||
func asText() -> String {
|
||||
return "A game of Snakes and Ladders with \(finalSquare) squares"
|
||||
}
|
||||
println(game.asText())
|
||||
// 输出 "A game of Snakes and Ladders with 25 squares"
|
||||
}
|
||||
println(game.asText())
|
||||
// 输出 "A game of Snakes and Ladders with 25 squares"
|
||||
```
|
||||
|
||||
<a name="declaring_protocol_adoption_with_an_extension"></a>
|
||||
## 通过延展补充协议声明
|
||||
|
||||
当一个类型已经实现了协议中的所有要求，却没有声明时，可以通过`扩展`来补充协议声明：
|
||||
|
||||
struct Hamster {
|
||||
var name: String
|
||||
func asText() -> String {
|
||||
return "A hamster named \(name)"
|
||||
}
|
||||
```swift
|
||||
struct Hamster {
|
||||
var name: String
|
||||
func asText() -> String {
|
||||
return "A hamster named \(name)"
|
||||
}
|
||||
extension Hamster: TextRepresentabl {}
|
||||
}
|
||||
extension Hamster: TextRepresentabl {}
|
||||
```
|
||||
|
||||
从现在起，`Hamster`的实例可以作为`TextRepresentable`类型使用
|
||||
|
||||
let simonTheHamster = Hamster(name: "Simon")
|
||||
let somethingTextRepresentable: TextRepresentabl = simonTheHamester
|
||||
println(somethingTextRepresentable.asText())
|
||||
// 输出 "A hamster named Simon"
|
||||
```swift
|
||||
let simonTheHamster = Hamster(name: "Simon")
|
||||
let somethingTextRepresentable: TextRepresentabl = simonTheHamester
|
||||
println(somethingTextRepresentable.asText())
|
||||
// 输出 "A hamster named Simon"
|
||||
```
|
||||
|
||||
> 注意：
|
||||
>
|
||||
> 注意：
|
||||
即时满足了协议的所有要求，类型也不会自动转变，因此你必须为它做出明显的协议声明
|
||||
|
||||
<a name="collections_of_protocol_types"></a>
|
||||
@ -392,16 +432,20 @@
|
||||
|
||||
协议类型可以被集合使用，表示集合中的元素均为协议类型：
|
||||
|
||||
let things: TextRepresentable[] = [game,d12,simoTheHamster]
|
||||
```swift
|
||||
let things: TextRepresentable[] = [game,d12,simoTheHamster]
|
||||
```
|
||||
|
||||
如下所示，`things`数组可以被直接遍历，并调用其中元素的`asText()`函数：
|
||||
|
||||
for thing in things {
|
||||
println(thing.asText())
|
||||
}
|
||||
// A game of Snakes and Ladders with 25 squares
|
||||
// A 12-sided dice
|
||||
// A hamster named Simon
|
||||
```swift
|
||||
for thing in things {
|
||||
println(thing.asText())
|
||||
}
|
||||
// A game of Snakes and Ladders with 25 squares
|
||||
// A 12-sided dice
|
||||
// A hamster named Simon
|
||||
```
|
||||
|
||||
`thing`被当做是`TextRepresentable`类型而不是`Dice`，`DiceGame`，`Hamster`等类型。因此能且仅能调用`asText`方法
|
||||
|
||||
@ -410,36 +454,42 @@
|
||||
|
||||
协议能够*继承*一到多个其他协议。语法与类的继承相似，多个协议间用逗号`,`分隔
|
||||
|
||||
protocol InheritingProtocol: SomeProtocol, AnotherProtocol {
|
||||
// 协议定义
|
||||
}
|
||||
```swift
|
||||
protocol InheritingProtocol: SomeProtocol, AnotherProtocol {
|
||||
// 协议定义
|
||||
}
|
||||
```
|
||||
|
||||
如下所示，`PrettyTextRepresentable`协议继承了`TextRepresentable`协议
|
||||
|
||||
protocol PrettyTextRepresentable: TextRepresentable {
|
||||
func asPrettyText() -> String
|
||||
}
|
||||
```swift
|
||||
protocol PrettyTextRepresentable: TextRepresentable {
|
||||
func asPrettyText() -> String
|
||||
}
|
||||
```
|
||||
|
||||
`遵循``PrettyTextRepresentable`协议的同时，也需要`遵循`TextRepresentable`协议。
|
||||
|
||||
如下所示，用`扩展`为`SnakesAndLadders`遵循`PrettyTextRepresentable`协议：
|
||||
|
||||
extension SnakesAndLadders: PrettyTextRepresentable {
|
||||
func asPrettyText() -> String {
|
||||
var output = asText() + ":\n"
|
||||
for index in 1...finalSquare {
|
||||
switch board[index] {
|
||||
case let ladder where ladder > 0:
|
||||
output += "▲ "
|
||||
case let snake where snake < 0:
|
||||
output += "▼ "
|
||||
default:
|
||||
output += "○ "
|
||||
}
|
||||
}
|
||||
return output
|
||||
}
|
||||
}
|
||||
```swift
|
||||
extension SnakesAndLadders: PrettyTextRepresentable {
|
||||
func asPrettyText() -> String {
|
||||
var output = asText() + ":\n"
|
||||
for index in 1...finalSquare {
|
||||
switch board[index] {
|
||||
case let ladder where ladder > 0:
|
||||
output += "▲ "
|
||||
case let snake where snake < 0:
|
||||
output += "▼ "
|
||||
default:
|
||||
output += "○ "
|
||||
}
|
||||
}
|
||||
return output
|
||||
}
|
||||
}
|
||||
```
|
||||
|
||||
在`for in`中迭代出了`board`数组中的每一个元素：
|
||||
|
||||
@ -449,9 +499,11 @@
|
||||
|
||||
任意`SankesAndLadders`的实例都可以使用`asPrettyText()`方法。
|
||||
|
||||
println(game.asPrettyText())
|
||||
// A game of Snakes and Ladders with 25 squares:
|
||||
// ○ ○ ▲ ○ ○ ▲ ○ ○ ▲ ▲ ○ ○ ○ ▼ ○ ○ ○ ○ ▼ ○ ○ ▼ ○ ▼ ○
|
||||
```swift
|
||||
println(game.asPrettyText())
|
||||
// A game of Snakes and Ladders with 25 squares:
|
||||
// ○ ○ ▲ ○ ○ ▲ ○ ○ ▲ ▲ ○ ○ ○ ▼ ○ ○ ○ ○ ▼ ○ ○ ▼ ○ ▼ ○
|
||||
```
|
||||
|
||||
<a name="protocol_composition"></a>
|
||||
## 协议合成
|
||||
@ -460,29 +512,30 @@
|
||||
|
||||
举个例子：
|
||||
|
||||
protocol Named {
|
||||
var name: String { get }
|
||||
}
|
||||
protocol Aged {
|
||||
var age: Int { get }
|
||||
}
|
||||
struct Person: Named, Aged {
|
||||
var name: String
|
||||
var age: Int
|
||||
}
|
||||
func wishHappyBirthday(celebrator: protocol<Named, Aged>) {
|
||||
println("Happy birthday \(celebrator.name) - you're \(celebrator.age)!")
|
||||
}
|
||||
let birthdayPerson = Person(name: "Malcolm", age: 21)
|
||||
wishHappyBirthday(birthdayPerson)
|
||||
// 输出 "Happy birthday Malcolm - you're 21!
|
||||
```swift
|
||||
protocol Named {
|
||||
var name: String { get }
|
||||
}
|
||||
protocol Aged {
|
||||
var age: Int { get }
|
||||
}
|
||||
struct Person: Named, Aged {
|
||||
var name: String
|
||||
var age: Int
|
||||
}
|
||||
func wishHappyBirthday(celebrator: protocol<Named, Aged>) {
|
||||
println("Happy birthday \(celebrator.name) - you're \(celebrator.age)!")
|
||||
}
|
||||
let birthdayPerson = Person(name: "Malcolm", age: 21)
|
||||
wishHappyBirthday(birthdayPerson)
|
||||
// 输出 "Happy birthday Malcolm - you're 21!
|
||||
```
|
||||
|
||||
`Named`协议包含`String`类型的`name`属性；`Aged`协议包含`Int`类型的`age`属性。`Person`结构体`遵循`了这两个协议。
|
||||
|
||||
`wishHappyBirthday`函数的形参`celebrator`的类型为`protocol<Named,Aged>`。可以传入任意`遵循`这两个协议的类型的实例
|
||||
|
||||
> 注意：
|
||||
>
|
||||
> 注意：
|
||||
`协议合成`并不会生成一个新协议类型，而是将多个协议合成为一个临时的协议，超出范围后立即失效。
|
||||
|
||||
<a name="checking_for_protocol_conformance"></a>
|
||||
@ -494,57 +547,64 @@
|
||||
* `as?`返回一个可选值，当实例`遵循`协议时，返回该协议类型；否则返回`nil`
|
||||
* `as`用以强制向下转换型。
|
||||
|
||||
```
|
||||
```swift
|
||||
@objc protocol HasArea {
|
||||
var area: Double { get }
|
||||
var area: Double { get }
|
||||
}
|
||||
```
|
||||
|
||||
|
||||
> 注意：
|
||||
>
|
||||
> 注意：
|
||||
`@objc`用来表示协议是可选的，也可以用来表示暴露给`Objective-C`的代码，此外，`@objc`型协议只对`类`有效，因此只能在`类`中检查协议的一致性。详情查看*[Using Siwft with Cocoa and Objectivei-c](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/BuildingCocoaApps/index.html#//apple_ref/doc/uid/TP40014216)*。
|
||||
|
||||
class Circle: HasArea {
|
||||
let pi = 3.1415927
|
||||
var radius: Double
|
||||
var area:≈radius }
|
||||
init(radius: Double) { self.radius = radius }
|
||||
}
|
||||
class Country: HasArea {
|
||||
var area: Double
|
||||
init(area: Double) { self.area = area }
|
||||
}
|
||||
```swift
|
||||
class Circle: HasArea {
|
||||
let pi = 3.1415927
|
||||
var radius: Double
|
||||
var area:≈radius }
|
||||
init(radius: Double) { self.radius = radius }
|
||||
}
|
||||
class Country: HasArea {
|
||||
var area: Double
|
||||
init(area: Double) { self.area = area }
|
||||
}
|
||||
```
|
||||
|
||||
`Circle`和`Country`都遵循了`HasArea`协议，前者把`area`写为计算型属性（computed property），后者则把`area`写为存储型属性（stored property）。
|
||||
|
||||
如下所示，`Animal`类没有实现任何协议
|
||||
|
||||
class Animal {
|
||||
var legs: Int
|
||||
init(legs: Int) { self.legs = legs }
|
||||
}
|
||||
```swift
|
||||
class Animal {
|
||||
var legs: Int
|
||||
init(legs: Int) { self.legs = legs }
|
||||
}
|
||||
```
|
||||
|
||||
`Circle,Country,Animal`并没有一个相同的基类，所以采用`AnyObject`类型的数组来装载在他们的实例，如下所示：
|
||||
|
||||
let objects: AnyObject[] = [
|
||||
Circle(radius: 2.0),
|
||||
Country(area: 243_610),
|
||||
Animal(legs: 4)
|
||||
]
|
||||
```swift
|
||||
let objects: AnyObject[] = [
|
||||
Circle(radius: 2.0),
|
||||
Country(area: 243_610),
|
||||
Animal(legs: 4)
|
||||
]
|
||||
```
|
||||
|
||||
如下所示，在迭代时检查`object`数组的元素是否`遵循`了`HasArea`协议：
|
||||
|
||||
for object in objects {
|
||||
if let objectWithArea = object as? HasArea {
|
||||
println("Area is \(objectWithArea.area)")
|
||||
} else {
|
||||
println("Something that doesn't have an area")
|
||||
}
|
||||
}
|
||||
// Area is 12.5663708
|
||||
// Area is 243610.0
|
||||
// Something that doesn't have an area
|
||||
```swift
|
||||
for object in objects {
|
||||
if let objectWithArea = object as? HasArea {
|
||||
println("Area is \(objectWithArea.area)")
|
||||
} else {
|
||||
println("Something that doesn't have an area")
|
||||
}
|
||||
}
|
||||
// Area is 12.5663708
|
||||
// Area is 243610.0
|
||||
// Something that doesn't have an area
|
||||
```
|
||||
|
||||
当数组中的元素遵循`HasArea`协议时，通过`as?`操作符将其`可选绑定(optional binding)`到`objectWithArea`常量上。
|
||||
|
||||
@ -559,36 +619,38 @@
|
||||
|
||||
像`someOptionalMethod?(someArgument)`一样，你可以在可选方法名称后加上`?`来检查该方法是否被实现。`可选方法`和`可选属性`都会返回一个`可选值(optional value)`，当其不可访问时，`?`之后语句不会执行，并返回`nil`。
|
||||
|
||||
> 注意：
|
||||
>
|
||||
> 注意：
|
||||
可选协议只能在含有`@objc`前缀的协议中生效。且`@objc`的协议只能被`类`遵循。
|
||||
|
||||
`Counter`类使用`CounterDataSource`类型的外部数据源来提供`增量值(increment amount)`，如下所示：
|
||||
|
||||
@objc protocol CounterDataSource {
|
||||
@optional func incrementForCount(count: Int) -> Int
|
||||
@optional var fixedIncrement: Int { get }
|
||||
}
|
||||
```swift
|
||||
@objc protocol CounterDataSource {
|
||||
@optional func incrementForCount(count: Int) -> Int
|
||||
@optional var fixedIncrement: Int { get }
|
||||
}
|
||||
```
|
||||
|
||||
`CounterDataSource`含有`incrementForCount`的`可选方法`和`fiexdIncrement`的`可选属性`。
|
||||
|
||||
> 注意：
|
||||
>
|
||||
> 注意：
|
||||
`CounterDataSource`中的属性和方法都是可选的，因此可以在类中声明但不实现这些成员，尽管技术上允许这样做，不过最好不要这样写。
|
||||
|
||||
`Counter`类含有`CounterDataSource?`类型的可选属性`dataSource`，如下所示：
|
||||
|
||||
@objc class Counter {
|
||||
var count = 0
|
||||
var dataSource: CounterDataSource?
|
||||
func increment() {
|
||||
if let amount = dataSource?.incrementForCount?(count) {
|
||||
count += amount
|
||||
} else if let amount = dataSource?.fixedIncrement? {
|
||||
count += amount
|
||||
}
|
||||
}
|
||||
}
|
||||
```swift
|
||||
@objc class Counter {
|
||||
var count = 0
|
||||
var dataSource: CounterDataSource?
|
||||
func increment() {
|
||||
if let amount = dataSource?.incrementForCount?(count) {
|
||||
count += amount
|
||||
} else if let amount = dataSource?.fixedIncrement? {
|
||||
count += amount
|
||||
}
|
||||
}
|
||||
}
|
||||
```
|
||||
|
||||
`count`属性用于存储当前的值，`increment`方法用来为`count`赋值。
|
||||
|
||||
@ -603,47 +665,57 @@
|
||||
|
||||
`ThreeSource`实现了`CounterDataSource`协议，如下所示：
|
||||
|
||||
class ThreeSource: CounterDataSource {
|
||||
let fixedIncrement = 3
|
||||
}
|
||||
```swift
|
||||
class ThreeSource: CounterDataSource {
|
||||
let fixedIncrement = 3
|
||||
}
|
||||
```
|
||||
|
||||
使用`ThreeSource`作为数据源开实例化一个`Counter`：
|
||||
|
||||
var counter = Counter()
|
||||
counter.dataSource = ThreeSource()
|
||||
for _ in 1...4 {
|
||||
counter.increment()
|
||||
println(counter.count)
|
||||
}
|
||||
// 3
|
||||
// 6
|
||||
// 9
|
||||
// 12
|
||||
```swift
|
||||
var counter = Counter()
|
||||
counter.dataSource = ThreeSource()
|
||||
for _ in 1...4 {
|
||||
counter.increment()
|
||||
println(counter.count)
|
||||
}
|
||||
// 3
|
||||
// 6
|
||||
// 9
|
||||
// 12
|
||||
```
|
||||
|
||||
`TowardsZeroSource`实现了`CounterDataSource`协议中的`incrementForCount`方法，如下所示：
|
||||
|
||||
class TowardsZeroSource: CounterDataSource {
|
||||
func incrementForCount(count: Int) -> Int {
|
||||
if count == 0 {
|
||||
return 0
|
||||
} else if count < 0 {
|
||||
return 1
|
||||
} else {
|
||||
return -1
|
||||
}
|
||||
}
|
||||
}
|
||||
```swift
|
||||
class TowardsZeroSource: CounterDataSource {
|
||||
func incrementForCount(count: Int) -> Int {
|
||||
if count == 0 {
|
||||
return 0
|
||||
} else if count < 0 {
|
||||
return 1
|
||||
} else {
|
||||
return -1
|
||||
}
|
||||
}
|
||||
}
|
||||
```
|
||||
|
||||
下边是执行的代码：
|
||||
|
||||
counter.count = -4
|
||||
counter.dataSource = TowardsZeroSource()
|
||||
for _ in 1...5 {
|
||||
counter.increment()
|
||||
println(counter.count)
|
||||
}
|
||||
// -3
|
||||
// -2
|
||||
// -1
|
||||
// 0
|
||||
// 0
|
||||
```swift
|
||||
counter.count = -4
|
||||
counter.dataSource = TowardsZeroSource()
|
||||
for _ in 1...5 {
|
||||
counter.increment()
|
||||
println(counter.count)
|
||||
}
|
||||
// -3
|
||||
// -2
|
||||
// -1
|
||||
// 0
|
||||
// 0
|
||||
```
|
||||
|
||||
preview
|
||||
Reference in New Issue
Block a user