Chapter 9. Modules and Namespaces
A Ruby module is nothing more than a grouping of objects under a single name. The objects may be constants, methods, classes, or other modules.
Modules have two uses. You can use a module as a convenient way to bundle
objects together, or you can incorporate its contents into a class with
When a module is used as a container for objects, it’s called a
Math module is a good example of a namespace: it
provides an overarching structure for constants like
Math::PI and methods like
Math::log, which would otherwise clutter up the
Kernel namespace. We cover this
most basic use of modules in Recipes
9.5 and 9.7.
Modules are also used to package functionality for inclusion in
Enumerable module isn’t supposed to be used on
its own: it adds functionality to a class like
Hash. We cover the use of modules as packaged
functionality for existing classes in Recipes 9.1 and 9.4.
Module is actually the superclass
Class, so every Ruby class is also a
module. Throughout this book we talk about using methods of
Module from within classes. The same methods
will work exactly the same way within modules. The only thing you can’t do
with a module is instantiate an object from it:
Class.superclass # => Module Math.class # => Module Math.new # NoMethodError: undefined method `new' for Math:Module
9.1. Simulating Multiple Inheritance with Mixins
You want to create a class that derives from two or ...