Swift4 func

###callback的运用 ######struct里的运用

class FinishAlertView{
    var buttonPressed : ((Int) -> Void)?
    func getNextPress(){
        buttonPressed?(2)
    }
}

struct PressCounter{
    var count = 0
    mutating func buttonPressed(at Index : Int){
        count += Index
    }
}

let finish = FinishAlertView()
var counter = PressCounter()
finish.buttonPressed = {counter.buttonPressed(at : $0)}

finish.getNextPress()
finish.getNextPress()
finish.getNextPress()
finish.getNextPress()
finish.getNextPress()
counter.count  // 10

######callback在class里的运用

class FinishAlertView{
    var buttonPressed : ((Int) -> Void)?
    func getNextPress(){
        buttonPressed?(2)
    }
}
class PressCounterClass {
    var count = 0
    func buttonPressed(at Index : Int){
        count += Index
    }
}
let finish = FinishAlertView()
var counterClass = PressCounterClass()
finish.buttonPressed = {[weak counterClass] index in // 防止循环引用
    counterClass?.buttonPressed(at: index)
}
finish.getNextPress()
finish.getNextPress()
finish.getNextPress()
finish.getNextPress()
finish.getNextPress()
counterClass.count // 10

###Closure Expressions和Closure