Modules Advanced in Ruby

Advanced mixin patterns, hooks, lookup order, and refinements.

include vs extend vs prepend

include adds instance methods; extend adds class methods; prepend inserts before the class in lookup (allowing method interception).

module Taggable
  def tag; :tagged end
end

class Post
  include Taggable
end

class Registry
  extend Taggable
end

Post.new.tag   # instance method
Registry.tag   # class method

module Loud
  def to_s; "LOUD:" + super end
end
class Name; def to_s = "name" end
class Name
  prepend Loud
end
Name.new.to_s  # => "LOUD:name"

Hooks

React to mixins with callbacks. Common hooks: included, extended, prepended, inherited, method_added.

module M
  def self.included(base); base.extend(ClassMethods) end
  module ClassMethods; def m!; :ok end end
end
class C; include M end
C.m!

Refinements

Scope monkey patches to specific files/contexts.

module Shout
  refine String do
    def shout; upcase + "!" end
  end
end

using Shout
"hi".shout  # => "HI!"

Visibility tweaks inside modules

You can mark selected methods as private when mixed in.

module Helpers
  def helper; :h end
  private :helper
end

Constant autoload

Defer constant loading until first use to reduce boot time.

module MyLib
  autoload :Parser, "my_lib/parser"
end

Summary

• Choose include/extend/prepend intentionally; prepend enables interception
• Use hooks to attach class‑level APIs; refinements to limit monkey patches
• autoload can improve load time by lazy‑loading constants