Swift协议（Protocol）

协议是为方法、属性等定义一套规范，没有具体的实现。
协议能够被类、结构体等具体实现（或遵守）。
 
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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 访问器
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 protocol SomeProtocol {
 var mustBeSettable:Int { get set }
var doesNotNeedToBeSettable: Int { get }
 }
 
2.静态属性
 
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protocol AnotherProtocol {
 class var someTypeProperty: Int { get set }
 }
 
3.只读
 
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protocol FullyNamed {
var fullName: String { get }
 }
 
 实例：
 
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struct Person: FullyNamed {
 varfullName: String
 }
 letjohn= Person(fullName: "John Appleseed")
 class Starship: FullyNamed {
 varprefix: String?
 varname: String
init(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
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 protocol RandomNumberGenerator{
func random() -> Double
}
 
2.定义静态方法
 
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 protocolSomeProtocol {
 class func someTypeMethod()
}
 
实例：
 
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protocol RandomNumberGenerator{
 funcrandom() -> Double
 }
 class LinearCongruentialGenerator:RandomNumberGenerator {
var lastRandom= 42.0let m = 139968.0
let a = 3877.0 let c = 29573.0
funcrandom() -> 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
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 protocol RandomNumberGenerator {
 func random() -> Double}
 class LinearCongruentialGenerator: RandomNumberGenerator {
 varlastRandom= 42.0 let m =139968.0
let a = 3877.0 letc = 29573.0
func random() -> Double {
lastRandom = ((lastRandom * a + c) %m)
 return lastRandom / m
}
}
class Dice {
 letsides: Int
let 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())")
}
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