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Ruby:Mixin

lastmod 2018-08-17created 2015-12-102 edits

Ruby has something called a Module, which is similar to a Class. Like a Class, a Module can contain methods, constants, modules, and classes. Unlike a Class, however, you cannot inherit from a module to create objects. But a class can use the instance methods of a Module. In this way, without inheritance, several Classes can mixin the same Module, or several Modules can be mixed into a single class.

Example

The example code has two Modules, Math and Stringfy, and mixes them into BigInteger, a class made by inheriting from the Number class, to add the modules' methods to the object.

The Math module has a method called add, which passes the sum of two numbers to BigInteger as the initial value. 

# filename : Math.rb

module Math  
  def add(value_one, value_two)
    BigInteger.new(value_one+value_two)
  end
end

The Stringfy module has a method called stringfy, which returns a string depending on the value of the object variable @value. 

#filename : Stringfy.rb

module Stringfy  
  def stringfy
    if @value == 1
      "One"
    elsif @value == 2
      "Two"
    elsif @value == 3
      "Three"
    end
  end
end

The Number class has a method called inteValue, which returns the @value object. 

# filename : Number.rb

class Number  
  def intValue
    @value
  end
end

The BigInteger class is made by inheriting from the Number class above; Stringfy is mixed into this class and it is extended with the Math methods. 

#filename : BigInteger.rb

require 'Stringfy'  
require 'Math'  
require 'Number'

class BigInteger < Number  
  include Stringfy
  extend Math

  def initialize(value)
    @value = value
  end
end

Let's test it. The code below simply uses BigInteger, passes the value 10 to the constructor to create an object, and prints the value of the @value object variable with intValue, which Number had. 

#filename test.rb
require 'BigInteger'

bigint1 = BigInteger.new(10)  
puts bigint1.intValue

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