Nil-coalescing

Swift provides the ?? operator for nil-coalescing. It unwraps Optionals and provides fallback or default values for the nil case.

For instance, a ?? b unwraps optional a if it has a value and returns a default value b if a is nil.

In this example, if optional a is not nil, the expression after the nil-coalescing operator is not going to be evaluated. Nil-coalescing is suitable for scenarios where we can provide a fallback or default value.