19. Traits

Traits represent a promise of a type. It combines the functionality of an abstract base class and an interface. A trait may define a set of Methods, with or without implementation, and instance variables.

A class may enforce fulfilment of a trait by inheriting it. By inheriting a trait, the class mixes in the set of methods and instance variables, while enforcing unimplemented methods are implemented. Traits may also inherit from each other in the same way as classes.

Trait ::=  "trait" identifier ClassInstructionSet "end"

trait Person
  name:String

  def new(n)
    name = n
  end
end

class Employee : Person
end

class Client : Person
end