**Course Title:** Ruby Programming: From Basics to Advanced Techniques **Section Title:** Modules, Mixins, and Gems **Topic:** Understanding modules and their uses ## Introduction to Modules ----------------------------- In Ruby, a module is a collection of methods, classes, and constants that can be used in other parts of a program. Modules are similar to classes, but they cannot be instantiated and do not support inheritance. Instead, they serve as a way to organize and reuse code. ## Defining a Module --------------------- A module is defined using the `module` keyword, followed by the name of the module. Here is a simple example of a module that contains a single method: ```ruby # Define a module called 'Greeting' module Greeting def self.hello puts "Hello, world!" end end ``` ## Using a Module ------------------ To use a module, you can include it in a class or another module using the `include` or `extend` keywords. ### Include When you include a module in a class, its methods become instance methods of the class. ```ruby # Include the Greeting module in a class class MyClass include Greeting end # Create an instance of MyClass and call the hello method obj = MyClass.new obj.hello # => undefined method `hello' (NoMethodError) ``` Because `hello` is a class method, you cannot call it on an instance of the class. Instead, you can define `hello` as an instance method: ```ruby module Greeting def hello puts "Hello, world!" end end ``` ```ruby # Create an instance of MyClass and call the hello method obj = MyClass.new obj.hello # => Hello, world! ``` ### Extend When you extend a module with another module, its methods become class methods. ```ruby # Extend a class with the Greeting module class MyClass extend Greeting end # Call the hello method on MyClass MyClass.hello # => Hello, world! ``` ## Use Cases for Modules ------------------------ ### Organizing Code Modules can help organize code by grouping related methods and classes together. ### Avoiding Namespace Pollution Modules can help avoid namespace pollution by providing a separate namespace for methods and classes. ### Creating Utilities Modules can be used to create utility modules that provide a set of reusable methods. ## Best Practices ------------------ * Use modules to organize code and avoid namespace pollution. * Define methods in modules as instance methods or class methods depending on their intended use. * Use `include` to add instance methods to a class and `extend` to add class methods. **Practical Exercise:** 1. Define a module called `MathUtils` with methods for performing mathematical operations, such as `add`, `subtract`, `multiply`, and `divide`. 2. Include the `MathUtils` module in a class called `Calculator` and demonstrate how to use its methods. **Additional Resources:** * [Ruby Documentation: Modules](https://ruby-doc.org/core-3.0.2/Module.html) * [Ruby Guides: Modules](https://rubyguides.com/2018/11/ruby-modules/) **Leave a comment or ask for help**: If you have any questions or need further clarification on any of the concepts covered in this topic, please don't hesitate to ask. We'll be happy to help. Next topic: 'Using mixins to add functionality.'