Blocks on Swift (animateWithDuration:animations:completion:)

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The completion parameter in animateWithDuration takes a block which takes one boolean parameter. In Swift, like in Obj-C blocks, you must specify the parameters that a closure takes:

UIView.animateWithDuration(0.2, animations: {
    self.blurBg.alpha = 1
}, completion: {
    (value: Bool) in
    self.blurBg.hidden = true
})

The important part here is the (value: Bool) in. That tells the compiler that this closure takes a Bool labeled ‘value’ and returns Void.

For reference, if you wanted to write a closure that returned a Bool, the syntax would be

{(value: Bool) -> bool in
    //your stuff
}

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