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协议是为方法、属性等定义一套规范。没有详细的实现。
协议可以被类、结构体等详细实现（或遵守）。
protocol SomeProtocol { // protocoldefinition goes here } struct SomeStructure: FirstProtocol, AnotherProtocol {// structure definition goes here}class SomeClass: SomeSuperclass, FirstProtocol, AnotherProtocol { // class definitiongoeshere }
属性
1. set 和 get 訪问器
protocol SomeProtocol { var mustBeSettable:Int { get set }var doesNotNeedToBeSettable: Int { get } }
2.静态属性
protocol AnotherProtocol { class var someTypeProperty: Int { get set } }
3.仅仅读
protocol FullyNamed {var fullName: String { get } }
实例：
struct Person: FullyNamed { varfullName: String } letjohn= Person(fullName: "John Appleseed") class Starship: FullyNamed { varprefix: String? varname: Stringinit(name: String, prefix: String? = nil) { self.name = name self.prefix = prefix} varfullName: String { return (prefix ? prefix!+ " " :"")+ name } } varncc1701 = Starship(name: "Enterprise",prefix: "USS")
方法
1.定义方法
protocol RandomNumberGenerator{func random() -> Double}
2.定义静态方法
protocolSomeProtocol { class func someTypeMethod()}
实例：
protocol RandomNumberGenerator{ funcrandom() -> Double } class LinearCongruentialGenerator:RandomNumberGenerator {var lastRandom= 42.0let m = 139968.0let a = 3877.0 let c = 29573.0funcrandom() -> Double { lastRandom = ((lastRandom * a + c) %m) returnlastRandom / m } } let generator= LinearCongruentialGenerator() println("Here's a random number:\(generator.random())") // prints "Here's a random number:0.37464991998171" println("And another one: \(generator.random())") //prints "And another one: 0.729023776863283"
把协议作为类型使用
protocol RandomNumberGenerator { func random() -> Double} class LinearCongruentialGenerator: RandomNumberGenerator { varlastRandom= 42.0 let m =139968.0let a = 3877.0 letc = 29573.0func random() -> Double {lastRandom = ((lastRandom * a + c) %m) return lastRandom / m}}class Dice { letsides: Intlet generator: RandomNumberGenerator init(sides: Int, generator: RandomNumberGenerator) { self.sides = sidesself.generator = generator}func roll() -> Int{return Int(generator.random() * Double(sides)) + 1}}vard6 = Dice(sides: 6, generator: LinearCongruentialGenerator())for_ in 1...5 {println("Randomdiceroll is \(d6.roll())")}