Optional requirements

There are times when we want protocols to define optional requirements. An optional requirement is a method or property that is not required to be implemented. To use optional requirements, we need to start off by marking the protocol with the @objc attribute.

To mark a property or method as optional, we use the optional keyword. The following example shows how we would create both an optional property and also an optional method:

@objc protocol Phone { 
  var phoneNumber: String {get set} 
  @objc optional var emailAddress: String {get set}  
  func dialNumber() 
  @objc optional func getEmail() 
} 

Now let's explore how protocol inheritance works.