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 Ruby’s
When a module is used as a container for objects, it’s called a namespace. Ruby’s
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 main
Kernel namespace. We cover this most basic use of modules in Recipes 10.5 and 10.7.
Modules are also used to package functionality for inclusion in classes. The
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 10.1 and 10.4.
Module is actually the superclass of
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:
# => Module
# => Module
# NoMethodError: undefined method `new' for Math:Module
You want to create a class that derives ...