Swift Functional Programming - Second Edition

Protocols as types

Any protocol that we define will become a fully-fledged type to use in our code. We can use a protocol as follows:

• A parameter type or return type in a function, method, or initializer
• The type of a constant, variable, or property
• The type of items in an array, dictionary, or another container

Let's look at the following example:

protocol ExampleProtocol {     var simpleDescription: String { get }     mutating func adjust() } // Classes, enumerations and structs can all adopt protocols. class SimpleClass: ExampleProtocol {     var simpleDescription: String = "A very simple class example"     var anotherProperty: Int = 79799     func adjust() {         simpleDescription += "Now 100% adjusted..."     } } var aSimpleClass = SimpleClass() aSimpleClass.adjust() ...