Swift 4 Protocol-Oriented Programming - Third Edition

Property requirements

A protocol can require that the conforming types provide certain properties with specified names and types. The protocol does not say whether the property should be a stored or computed property because the implementation details are left up to the conforming types.

When defining a property within a protocol, we must specify whether the property is a read-only or a read-write property by using the get and set keywords. We also need to specify the property's type since we cannot use the type inference in a protocol. Let's look at how we would define properties within a protocol by creating a protocol named FullName, as shown in the next example:

protocol FullName { var firstName: String {get set} var lastName: String ...