Protocol composition

We can declare types to conform to more than one protocol, creating a type that satisfies the requirements of both protocols. This is called protocol composition.

Let's first declare another protocol:

protocol Pensive 
{ 
  func reactToStimulus() 
} 

Now we can declare a type that conforms to both the Talkative and Pensive protocols:

struct Philosopher: Talkative, Pensive 
{ 
  func sayHi() 
  { 
    print("hi") 
  } 

  func reactToStimulus() 
  { 
    print("I thing therefore I am") 
  } 
} 

The syntax of declaring protocol compliance looks much like the syntax for declaring subclasses, but value types cannot inherit from other types (that is, declare themselves as subclasses). However, adopting a protocol is to all intents and purposes a form of inheritance.