Getting a list of classes that include a module

Question

I have a mixin for which I would like to get a list of all the classes that have included it. In the mixin module, I did the following:

module MyModule   def self.included(base)     @classes ||= []     @classes << base.name   end    def self.classes     @classes   end end  class MyClass   include MyModule end 

This works pretty well:

> MyModule.classes #=> nil > MyClass.new #=> #<MyClass ...> > MyModule.classes #=> ["MyClass"] 

Now, I would like to extract this part out into a separate module that can be included in my other mixins. So, I came up with the following:

module ListIncludedClasses   def self.included(base)     p "...adding #{base.name} to #{self.name}.classes"      @classes ||= []     @classes << base.name      base.extend(ClassMethods)   end    def self.classes     @classes   end    module ClassMethods     def included(module_base)       p "...adding #{module_base.name} to #{self.name}.classes"        @module_classes ||= []       @module_classes << module_base.name       super(module_base)     end     def classes       @module_classes     end   end  end  module MyModule   include ListIncludedClasses end 

This doesn't work though, because the #included(module_base) method being added to MyModule from ListIncludedClasses is never getting run. Interestingly enough, it does successfully add #classes to MyModule.

> MyModule.classes #=>    "...adding Rateable to ListIncludedClasses.classes"   => nil  > ListIncludedClasses #=> ["MyModule"] > MyClass.new #=> #<MyClass ...> # ^^ THIS SHOULD BE ADDING MyClass TO MyModule.classes ^^ > MyModule.classes #=> nil 

What am I missing?

Answer 1

module MyMod; end  class A; include MyMod; end class B < A; end class C; end  ObjectSpace.each_object(Class).select { |c| c.included_modules.include? MyMod }   #=> [B, A] 

Answer 2

Actually, your module extension module works. The problem is in your test: when you created a random unnamed class with Class.new, you forgot to include MyModule. As a side note, you can take your read-only accessor for classes that include the module and use the helpful Module#attr_reader method.