swift基础之扩展现有类、结构体、枚举

原创
2021/04/16 11:08
阅读数 131

扩展计算属性

//扩展 Double 计算属性
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")
//One inch is 0.0254 meters

let threeFeet = 3.ft
print("Three feet is \(threeFeet) meters")
//Three feet is 0.914399970739201 meters

扩展初始化器

//扩展初始化器
struct Rect{
    var x = 0.0, y = 0.0
    var width = 0.0, height = 0.0
}

extension Rect {
    init(pos: [Double], size: [Double]) {
        self.init(x: pos[0], y: pos[1], width: size[0], height: size[1])
    }
}

let r = Rect(pos: [0.0, 0.0], size: [4.0, 4.0])

扩展方法

//扩展方法
extension Int {
    func repeatTalk(talk: () -> Void) {
        for _ in 0..<self {
            talk()
        }
    }
}

5.repeatTalk {
    print("Hi")
}
/*
 Hi
 Hi
 Hi
 Hi
 Hi
 */

修改实例本身 mutating

//修改实例本身 mutating
extension Int {
    mutating func square() {
        self = self * self
    }
}

var a = 5
a.square()
print(a)
//25

扩展下标

//扩展下标
extension Int {
    subscript(index: Int) -> Int {
        var base = 1
        for _ in 0..<index {
            base *= 10
        }
        return (self/base) % 10
    }
}
print(12345678[0])
print(12345678[1])
print(12345678[2])
print(12345678[3])
print(12345678[4])
/*
 8
 7
 6
 5
 4
 */

扩展内嵌类型

//扩展内嵌类型
extension Int {
    enum Kind {
        case negative, zero, positive
    }
    
    var kind: Kind {
        switch self {
        case 0:
            return .zero
        case let x where x > 0:
            return .positive
        default:
            return .negative
        }
    }
}

print(4.kind)
//positive
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