The Book of Ruby

Included Modules, or “Mixins”

An object can access the instance methods of a module by including that module using the include method. If you were to include MyModule in your program, everything inside that module would suddenly pop into existence within the current scope. So, the greet method of MyModule will now be accessible:

modules2.rb

include MyModule

Note that only instance methods are included. In the previous example, the greet (instance) method has been included, but the MyModule.greet (module) method has not. As it’s included, the greet instance method can be used just as though it were a normal instance method within the current scope, whereas the module method, also named greet, is accessed using dot notation:

puts( greet ) #=> I'm happy. ...