From: Robert Klemme <bob.news@...>
Date: 2005-10-24T20:32:01+09:00
Subject: Re: How to find all the subclasses of a class?

Horacio Sanson wrote:
> I want to be able to list and instatiate all subclasses of a class to
> create a Factory type pattern,  I want to be able to do something like
>
>
> subclasses = Array.new
>
> ## Magic code that puts all subclasses of a class in
> ##  the subclasses array
> subclasses = get_subclasses( .... )
>
> subclasses.each { |subclass|
> return subclass.new if condition == true
> end
>
>
> sorry I am very new to Ruby and have no idea on how to do this.
> any help is appreciated.

There are two possible approaches:

1. Find them when you need them via ObjectSpace:

>> cl = Enumerable
=> Enumerable
>> subclasses = []
=> []
>> ObjectSpace.each_object(Module) {|m| subclasses << m if
m.ancestors.include? cl}
=> 371
>> subclasses
=> [Struct::Tms, Dir, File, IO, Range, Struct, Hash, Array, String,
Enumerable]

2. Record them when they are created.

This is typically done by a variant that uses Class#inherited.

>> class Foo
>> def self.inherited(cl)
>> p cl
>> end
>> end
=> nil
>> class Bar < Foo
>> end
Bar
=> nil

Kind regards

    robert