This form of the operator will trigger a runtime error if you try to downcast to an incorrect class type. Use the forced form of the type cast operator (as!) only when you are sure that the downcast will always succeed. This enables you to check for a successful downcast. This form of the operator will always return an optional value, and the value will be nil if the downcast was not possible. is an extraordinarily safe language, featuring guaranteed memory initialization, overflow checking, memory management with reference counting, and no billion. Use the conditional form of the type cast operator (as?) when you are not sure if the downcast will succeed. The forced form, as!, attempts the downcast and force-unwraps the result as a single compound action. The conditional form, as?, returns an optional value of the type you are trying to downcast to. Where you believe this is the case, you can try to downcast to the subclass type with a type cast operator (as? or as!).īecause downcasting can fail, the type cast operator comes in two different forms. # DowncastingĪ constant or variable of a certain class type may actually refer to an instance of a subclass behind the scenes.

These two operators provide a simple and expressive way to check the type of a value or cast a value to a different type. Type casting in Swift is implemented with the is and as operators. Type casting is a way to check the type of an instance, or to treat that instance as a different superclass or subclass from somewhere else in its own class hierarchy. Let value : Any = 'George' if let name = value as ? String # Type casting in Swift Language # Type Casting Generate UIImage of Initials from String.

Function as first class citizens in Swift.

Getting Started with Protocol Oriented Programming.Example of using a downcast on a function parameter involving subclassing.

Swift downcast initializer