One issue with Swift Closure
Here I have a simple snippet to use a simple animation with my specific UIView.
UIView.animateWithDuration(0.1) { [weak self] in
self?.popOverView.center = gesture.locationInView(self?.view)
}
Here [weak me] is to avoid the reference loop, and I also use trailing closure for code only. Howerver, the compiler is unhappy with this and gives me the wrong message.
Cannot invoke 'animateWithDuration' with an argument list of type '(FloatLiteralConvertible, () -> () -> $T2)'
What does $ T2 mean? And the odd thing is that when there are two or more statements in the closure body, it compiles correctly.
UIView.animateWithDuration(0.1) { [weak self] in
println()
self?.popOverView.center = gesture.locationInView(self?.view)
}
And I know that if there is only one statement in the closing body, it automatically returns.
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The single body of a statement in a closure has an implicit return, so what happens is that the compiler tries to establish the result of this statement:
self?.popOverView.center = gesture.locationInView(self?.view)
as a return value. You can fix this by adding an explicitreturn
self?.popOverView.center = gesture.locationInView(self?.view)
return
This only happens for single statements, so it works correctly in your second case
More information: Implicit returns from single-expression closures
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