What are modules used for in Ruby?

Modules in Ruby are used for two main purposes:

1. Namespaces: Organizing code to prevent name conflicts. They allow grouping related classes, methods, and constants under a single name. This helps avoid situations where two different classes or methods have the same name.

   # module_for_namespace.rb
   module MyFramework
     class Validator
       def validate(data)
         # validation logic
       end
     end
   end
   
   # another_file.rb
   # To use Validator from MyFramework:
   validator = MyFramework::Validator.new
   validator.validate("some data")
   

2. Mixins: A mechanism for sharing functionality (methods) among multiple classes without using classical inheritance. Modules are included in classes using include or prepend.

   • include: Module methods become available in class instances and can be overridden in the class itself. Method lookup order: current class, included module, superclasses.
   • prepend: Inserts the module into the inheritance chain before the class. Module methods have priority over class methods.

   Example of using include:

   # mixin_module.rb
   module Loggable
     def log(message)
       puts "[LOG] #{message}"
     end
   end
   
   # class_using_mixin.rb
   class MyClass
     include Loggable # Including Loggable module
   
     def process_data
       log("Processing data...") # Using method from module
       # other logic
     end
   end
   
   obj = MyClass.new
   obj.process_data
   

   Example of using prepend:

   # mixin_module.rb
   module MyPrependedModule
     def greet
       puts "Hello from module!"
     end
   end
   
   # class_with_prepend.rb
   class MyPrependClass
     prepend MyPrependedModule # Module will be before class in inheritance chain
   
     def greet
       puts "Hello from class!"
     end
   end
   
   obj = MyPrependClass.new
   obj.greet # Will output "Hello from module!" because module method has priority
   

Modules cannot be instantiated (objects of modules cannot be created) and do not have an inheritance chain in the same sense as classes.