Modules and mixins in Ruby

Sharing behavior across classes without inheritance.

# a module holds behavior; include mixes it into any class
module Greetable
  def greet
    "hi, I am #{display_name}"
  end
end

class Robot
  include Greetable

  def initialize(id)
    @id = id
  end

  def display_name
    "unit-#{@id}"
  end
end

puts Robot.new(7).greet

How it works

1. A module defines methods with no class of their own.
2. include mixes the module into a class as instance methods.
3. The mixin calls display_name, which the host class provides.

Keywords and builtins used here

• Robot
• class
• def
• display_name
• end
• greet
• id
• initialize
• module
• puts

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Step 3 of 3 in Classes & modules, step 21 of 29 in Language basics.

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