Extending existing types with a protocol

We can declare a type that we haven't declared ourselves, including Swift's own types, to conform to our custom protocol by using an extension:

extension Int: Talkative 
{ 
  func sayHi() 
  { 
    print("Hey, I'm \(self)") 

    if self%2 != 0 
    { 
      print("Isn't that odd?") 
    } 
  } 
} 

We can now call the sayHi method on any int:

1.sayHi() 

This is something you couldn't do with subclassing--we now have the ability to customize any and all Swift types in any way that we need to, including primitives such as Int and Double.