What does the parenthesis in Swift does..

http://stackoverflow.com/questions/24071334/blocks-on-swift-animatewithdurationanimationscompletion

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
}