Swift 4中的可选闭包

Question

我需要一个按需执行的闭包方法。

在Swift 3中我曾经做过类似的事情：

// Declare closure
var checksPerformed: ((Void) -> Void)? // Declaration

// Call when needed
checksPerformed?() 

//Only executes when checksPerformed is called
checksPerformed = { _ in 
    // do stuff here
}

在Swift 4中，情况已不再如此。

修好此警告后，没有任何作用。 这样做的新方法是什么？

如果我要将声明更新为：var checksPerformed: (() -> ())?我正在

Answer 1

Distinguish between single-tuple and multiple-argument function types

// Declare closure
var checksPerformed: (() -> ())? // Declaration

// Call when needed
checksPerformed?()

//Only executes when checksPerformed is called
checksPerformed = {
    // do stuff here
}

Answer 2

使用

var checksPerformed: (()->(Void))?

如果你这样做，一切都应该按预期工作。

在分配闭包时不要使用_ in：

//Only executes when checksPerformed is called
checksPerformed = { 
    // do stuff here
}

//Call when needed
checksPerformed?()