(十三) [Swift]Swift中的Closure

1.完整的定义一个closure

var addClosure : (Int,Int) ->Int = {
    (a:Int,b:Int)
    in
    return a + b
}

省略参数类型

addClosure = { a,b in return a + b}

单语句closure可以省略return

addClosure = { a,b in a + b}

终极简化，将参数用$1,$2的形式简化

addClosure = { $0 + $1 }

2.closure入参，并与函数相比较

func excute(a:Int,_ b:Int,operation:(Int,Int)->Int) -> Int {
    return operation(a,b)
}
func multi(a:Int,_ b:Int) -> Int{
    return a * b
}

//closure入参

excute(1, 2, operation: addClosure)

//函数入参
excute(1, 2, operation: multi)

closure 匿名入参

excute(1, 2, operation: {a,b in a + b})

closure 匿名入参 简化

excute(1, 2, operation: { $0 + $1 })

closure 匿名入参,如果closure参数在最后一个，则可以将closure写在函数的参数列表的外边

excute(1, 2) { (a, b) -> Int in
    a + b
}

excute(1, 2) { $0 + $1 }

3.如果closure没有返回值，则必须标明Void 而不能像函数一样省略

let addClosure2 : (Int,Int) -> Void = {
  print($0 + $1)
}

4.捕获变量，closure可以捕获变量

func counting() -> () ->Int {
    var count = 0 ;
    let incrementCount : ()->Int = {
        count += 1
        return count
    }
    return incrementCount;
}

var c1 = counting()
c1()   //1
c1()   //2
c1()   //3

var c2 = counting()
c2()   //1
c2()   //2
c2()   //3

其实func也可以

func counting2() -> () ->Int {
    var count = 0 ;
    func incrementCount() ->Int {
        count += 1
        return count
    }
    return incrementCount;
}
var c21 = counting2()
c21()   //1
c21()   //2
c21()   //3

var c22 = counting2()
c22()   //1
c22()   //2
c22()   //3

5.closure和函数相比

• closure就是一个没有名字的函数
• closure可以没有名字
• closure不能省略Void