optional closure property in Swift

I believe you just need to wrap the closure type in parenthesis, like so:

var respondToButton:((sender: UIButton) -> Bool)?

Alternatively if this is a closure type you're going to use often you can create a typealias to make it more readable:

typealias buttonResponder = (sender: UIButton) -> Bool

then in your class:

var respondToButton:buttonResponder?

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