Swift的where用法

where关键词

Swift用where关键词来指定一些特殊情况

指定Generic Type 和 where的AND用法

代表入参数必须同时是UIView和NSObject

func genericFunc<T>(param:T) where T:UIView, T:NSObject{
        print("Input parameter is enter")
}

genericFunc(param: UIView()) //可以执行

如果使用另外一个入参，将会提示错误

genericFunc(param: NSObject())

// error: cannot convert value of type 'NSObject' to expected argument type 'UIView' genericFunc(param: NSObject()) as! UIView

指定Protocol的Extension类型

针对同一个Protocol和不同的Class进行公用时，来完成不同的实现

protocol SomeProtocol {
    func protocolFunc()
}

extension SomeProtocol where Self: UIView {
    func protocolFunc() {
        print("This Extension for UIView")
    }
}

extension SomeProtocol where Self: CALayer {
    func protocolFunc() {
        print("This Extension for CALayer")
    }
}

class ViewTest: UIView, SomeProtocol {}
class LayerTest: CALayer, SomeProtocol {}

let tempView: ViewTest = ViewTest()
let tempLayer: LayerTest = LayerTest()

tempView.protocolFunc()  //"This Extension for UIView"
tempLayer.protocolFunc() //"This Extension for CALayer"

与其他控制流函数结合

也可以用于过滤控制流里的某些条件

//do....catch...
do{
    try throwError()
}catch ExceptionError.httpCode(let httpCode) where httpCode >= 500{
    print("server error")
}

//switch
switch value {
case let x where x < 60:
default:
}

//for
for i in numbers where i > 3 {
}

赏

请问老板还招人么(/ω＼)

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