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 {get set} 
} 

In this example, we define two properties named firstName and lastName, which are read-write properties. Any type that conforms to this protocol must implement both of these properties. If we wanted to define the property as read-only, we would define it using only the get keyword, as shown in the following code:

var readOnly: String {get} 

It is possible to define static properties by using the static keyword, as shown in the following example:

static var typeProperty: String {get} 

Now let's see how we would add method requirements to our protocol.