From: Rick DeNatale <rick.denatale@...>
Date: 2006-09-02T06:28:41+09:00
Subject: Re: [Q] How can I ask to which module a method belongs to?

On 9/1/06, Markus Gaelli <gaelli@emergent.de> wrote:
> Hi List,
>
> more questions from a Ruby-Newbie...
>
> Sam Roberts from Ruby-Core answered to my original question:
> >> I am aware of Singleton Methods, but as they can extend instances,
> >> (how) can I extend classes without changing their original class
> >> definition in Ruby?
> >>
> >
> > This is probably best posted to ruby-talk, not ruby-core, folks would
> > likely be quite interested.
> >
> > classes are "open" in ruby, you can add methods as you wish.
> >
> > irb(main):001:0> s = "hi"
> > => "hi"
> > irb(main):002:0> class String; def this(opt) puts(self+opt) end end
> > => nil
> > irb(main):003:0> s.this(" that")
> > hi that
> > => nil
> > irb(main):004:0> "bye".this(" that")
> > bye that
> > => nil
> >
> > Cheers,
> > Sam
>
> That is good news to me. But now I wonder, if and how I can ask e.g.
> String#this(opt) in which module it is defined.

First note, that a method can be defined in a module or a class, and
that a class is a kind of module.

I haven't tested this extensively but I think it works.  It searches
for a method name in a class the same way that methods are found at
runtime, at each level of the class hierarchy, the class is searched,
then any modules that class includes in the reverse order they were
included.  This code depends on Module#included_modules giving it's
result in the right order, which a few quick tests seems to indicate:
 module A
end
 module B
 end
module C
    include B
    include A
end

C.included_modules => [A, B]
module D
    include A
    include B
end
 D.included_modules => [B, A]

Okay so here's my code:

class Module
        def module_defining(method_name)
                method_name = method_name.to_s
                return self if instance_methods(false).include?(method_name)
                included_modules.each do |mixin|
                        answer = mixin.module_defining(method_name)
                        return answer if answer
                end
                nil
        end
end

class Class
        def module_defining(method_name)
                answer = super
                return answer if answer
                return superclass.module_defining(method_name) if superclass
        end
end

irb(main):001:0> load 'moddefining.rb'
=> true
irb(main):002:0> String.module_defining('==')
=> String
irb(main):003:0> String.module_defining('id')
=> Kernel
irb(main):004:0> String.module_defining('map')
=> Enumerable



-- 
Rick DeNatale

My blog on Ruby
http://talklikeaduck.denhaven2.com/