Swift version: 5.10
Optional chaining is a Swift feature that allows execution of a statement to stop and return nil at any point. For example, all views have an optional superview
property that stores whichever UIView
contains it, all UIView
has an optional gestureRecognizer
array that stores the gesture recognizers it has, and all arrays have an optional first
property that returns the first item.
Optional chaining allows us to put those three optionals together like this:
let firstParentRecognizer = view.superview?.gestureRecognizers?.first
So, superview
is optional, gestureRecognizers
is optional, and first
is optional, but the end result – firstParentRecognizer
will be a simple UIGestureRecognizer?
rather than a triple optional. The optional chaining – the two question marks – mean that if superview
is nil then firstParentRecognizer
gets set to nil and the rest of the statement is ignored, and the same is true of gestureRecognizers
.
Without optional chaining we’d need to use a pyramid of if let
statements, like this:
if let superview = view.superview {
if let recognizers = superview.gestureRecognizers {
let firstParentRecognizer = recognizers.first
}
}
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Available from iOS 8.0
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