Ruby Mixin

8th Light Apprenticeship - Day 70

Modules in Ruby are used to group together methods, classes and constants. Primarily they provide a namespace but they also enable Mixin’s to be used. Similar to classes, modules are defined using the module keyword.

module Hello
  def Hello.say_hi
      "hi"
  end
end

To use the module functionality in a different class, the include keyword must be used. Like with constants, the statements inside Hello can be accessed in Greeting using the :: functionality

class Greeting 
  include Hello
  
  def greet
     puts Hello::say_hi
  end
def

If the module is defined in a separate class, then it must also be imported using the require statement.

Another use for modules is mixins. This is where a class can inherit features from more than one parent class, and can be used to model something similar to multiple inheritance.

module Greet
  def say_hello
      "hello"
  end
end

class Welcome
  include Greet
  
  def politely_say_good_morning
     puts say_hi + ", Good Morning."
  end
end

The class Welcome consists of the say_hello and the politely_say_good_morning methods. say_hello is essentially inherited and can be used as thought it is an instance method of the Welcome class itself.

You can not create an instance of a module, i.e. ` Greet.new` will not work, therefore all entities are best modelled as classes.

To conclude, a class can only have one superclass (using the < symbol), but it can mix in as many modules as it wants.