Swift Functional Programming - Second Edition

Type checking and casting

Swift provides type checking and type casting. We can check the type of a variable with the is keyword. It is most commonly used in if statements, as shown in the following code:

let aConstant = "String" if aConstant is String {     print("aConstant is a String") } else {     print("aConstant is not a String") }

As String is a value type and the compiler can infer the type, the Swift compiler will issue a warning because it already knows that aConstant is String. Another example can be the following, where we check whether anyString is String:

let anyString: Any = "string" if anyString is String {     print("anyString is a String") } else {     print("anyString is not a String") }

Using the is operator is useful to check ...