From: "apotonick (Nick Sutterer)" <apotonick@...>
Date: 2012-10-31T19:45:40+09:00
Subject: [ruby-core:48657] [ruby-trunk - Feature #7240] Inheritable #included/#extended Hooks For Modules


Issue #7240 has been updated by apotonick (Nick Sutterer).


=begin
Ah ok, now I understand you, Alexey. Instead of having a keyword (inclusive/inheritable) you want to have a special "namespace" as in

  module M
    def to_be_inherited.m; end

which would include the class method #m when including M? Cool. However, how would we make self.included "inheritable" then?

> I wonder what the core developers would say.
I talked to Matz at the Sapporo RubyKaigi this year and he made me file this issue!
=end

----------------------------------------
Feature #7240: Inheritable #included/#extended Hooks For Modules
https://bugs.ruby-lang.org/issues/7240#change-32087

Author: apotonick (Nick Sutterer)
Status: Open
Priority: Normal
Assignee: 
Category: 
Target version: 


An inheritable hook mechanism for modules would be a great way for module/gem authors to simplify their implementations.


The Problem
-----------

Let's say I have the following module.

  module A
    def self.included(base)
      # add class methods to base
    end
  end

So, A is overriding the #included hook to add class methods to base.

module B
  include A

  # class methods from A are here.
end

Since B is including A, A's #included method is invoked and A's class methods will be copied to B.

module C
  include B

  # class methods from B are lost.
end

When including B into C, B's #included is invoked and A's #included is lost. In our example, this means no class methods from A are in C.


Proposal
--------

It would be cool if #included/#extended in a module could be inherited to including descendants. I wrote a small gem "uber" that does this kind of stuff with a simple recursion. Roughly, it works like this.

  module A
    extend InheritableIncluded # "execute my #included everytime me or my descendents are included."

    def self.included(base)
      # add class methods to base
    end
  end

Now, A's #included is invoked every time it or a descending module is included. In our example, class methods from A would be around in C.

When discussing this with Matz we agreed that this might be really useful in Ruby itself. I'm just not sure how to mark inheritable hooks.


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