Swift 4 Protocol-Oriented Programming - Third Edition

Using protocols as a type

Even though no functionality is implemented in a protocol, they are still considered a full-fledged type in the Swift programming language, and can mostly be used like any other type. What this means is that we can use protocols as parameters or return types for a function. We can also use them as the type for variables, constants, and collections. Let's look at some examples of this. For these next few examples, we will use the following Person protocol:

protocol Person { 
  var firstName: String {get set} 
  var lastName: String {get set}  
  var birthDate: Date {get set}  
  var profession: String {get} 
  init (firstName: String, lastName: String, birthDate: Date) 
} 

In this Person protocol, we define four properties and one ...