This is behaviour that has been introduced in Swift 3. Instead of having to explicitly annotate functions with @warn_unused_result
in order to tell the compiler that the result should be used by the caller, this is now the default behaviour.
You can use the @discardableResult
attribute on your function in order to inform the compiler that the return value doesn’t have to be ‘consumed’ by the caller.
@discardableResult
func makeConstraint(withAnotherView : UIView) -> NSLayoutConstraint {
... // do things that have side effects
return NSLayoutConstraint()
}
view1.makeConstraint(view2) // No warning
let constraint = view1.makeConstraint(view2) // Works as expected
You can read about this change in more detail on the evolution proposal.