extension SomeType {
// new functionality to add to SomeType goes here
}
扩展可以使已有的类型遵循一个或多个协议。在这种情况下,协议名的书写方式与类或结构体完全一样:
extension SomeType: SomeProtocol, AnotherProtocol {
// implementation of protocol requirements goes here
}
extension Double {
var km: Double { return self * 1_000.0 }
var m: Double { return self }
var cm: Double { return self / 100.0 }
var mm: Double { return self / 1_000.0 }
var ft: Double { return self / 3.28084 }
}
let oneInch = 25.4.mm
print("One inch is \(oneInch) meters")
let threeFeet = 3.ft
print("Three feet is \(threeFeet) meters")
extension Rect {
init(center: Point, size: Size) {
let originX = center.x - (size.width / 2)
let originY = center.y - (size.height / 2)
self.init(origin: Point(x: originX, y: originY), size: size)
}
}
let centerRect = Rect(center: Point(x: 4.0, y: 4.0),
size: Size(width: 3.0, height: 3.0))
extension Int {
func repetitions(task: () -> Void) {
for _ in 0..<self {
task()
}
}
}
3.repetitions {
print("Hello!")
}
extension Int {
mutating func square() {
self = self * self
}
}
var someInt = 3
someInt.square()
//RandomNumberGenerator 是一个协议
extension RandomNumberGenerator {
func randomBool() -> Bool {
return random() > 0.5
}
}
针对某个需要实现的功能,可以使用协议定义出接口,然后利用协议扩展提供默认的实现。需要这个功能,只需要声明遵守了这个协议即可,遵守某个协议的对象调用协议声明的方法时,如果类本身没有提供实现,协议扩展提供的默认实现会被调用。
protocol Eat {
func eat()
}
class Person: Eat {
func eat() {
print("吃饭了")
}
}
var p = Person()
p.eat()
extension Eatable {
func eat() {
print("吃饭了")
}
}
class Person: Eatable {
}
var p = Person()
p.eat()
class Person: Eatable {
func eat() {
print("人要吃饭了")
}
}
var p = Person()
p.eat()
protocol Coder {
var haveFun:Bool {get set}
var ownMoney:Bool {get set}
}
protocol Swifter {
var codingLevel:Int {get set}
}
struct CoderA : Coder {
var name:String
var haveFun: Bool
var ownMoney: Bool
}
struct CoderB : Coder, Swifter {
var name:String
var haveFun: Bool = true
var ownMoney: Bool = true
var codingLevel: Int = 3
}
struct CoderC : Coder, Swifter{
var name:String
var haveFun: Bool = true
var ownMoney: Bool = true
var codingLevel: Int = 5
}
可以发现CoderB与CoderC有冗余
protocol Coder {
var haveFun:Bool {get set}
var ownMoney:Bool {get set}
}
protocol Swifter {
var codingLevel:Int {get set}
}
//where限定条件
extension Coder where Self:Swifter {
var haveFun:Bool { return true}
var ownMoney:Bool { return true}
}
struct CoderA : Coder {
var name:String
var haveFun: Bool
var ownMoney: Bool
}
struct CoderB : Coder, Swifter {
var name:String
var haveFun: Bool
var ownMoney: Bool
var codingLevel: Int = 3
}
struct CoderC : Coder, Swifter{
var name:String
var haveFun: Bool
var ownMoney: Bool
var codingLevel: Int = 5
}