Even though no functionality is implemented in a protocol, they are still considered a full-fledged type in the Swift programming language and can be used like any other type. What this means is we can use protocols as a parameter type or as a return type in a function. We can also use them as the type for variables, constants, and collections. Let's take a look at some examples. For these few examples, we will use the PersonProtocol protocol:
protocol PersonProtocol {
var firstName: String {get set}
var lastName: String {get set}
var birthDate: NSDate {get set}
var profession: String {get}
init (firstName: String, lastName: String, birthDate: NSDate)
}
In this first example, we will see how we can use protocols as a parameter type or return type in functions, methods, or initializers:
func updatePerson(person: PersonProtocol) -> PersonProtocol {
// Code to update person goes here ...