# How can I ask to which module a method belongs to? **URL:** \ **Category:** Ruby\ **Created:** [September 1, 2006, 11:41am UTC](https://www.ruby-forum.com/t/how-can-i-ask-to-which-module-a-method-belongs-to/67197 "2006-09-01T11:41:38Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![dk3qu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/d2c977/32.png) [@dk3qu](https://www.ruby-forum.com/u/dk3qu)\ **Post date:** [September 1, 2006, 11:41am UTC](https://www.ruby-forum.com/t/how-can-i-ask-to-which-module-a-method-belongs-to/67197/1 "2006-09-01T11:41:38Z")
Hi List, more questions from a Ruby-Newbie… Sam R. from Ruby-Core answered to my original question: > irb(main):001:0\> s = “hi” > 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. Any ideas? Cheers, Markus ---
**Author:** ![dk3qu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/d2c977/32.png) [@dk3qu](https://www.ruby-forum.com/u/dk3qu)\ **Post date:** [September 1, 2006, 11:39pm UTC](https://www.ruby-forum.com/t/how-can-i-ask-to-which-module-a-method-belongs-to/67197/2 "2006-09-01T23:39:43Z")
On 9/1/06, Markus G. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > This is probably best posted to ruby-talk, not ruby-core, folks would > > =\> 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/](http://talklikeaduck.denhaven2.com/) ---
**Author:** ![dk3qu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/d2c977/32.png) [@dk3qu](https://www.ruby-forum.com/u/dk3qu)\ **Post date:** [September 1, 2006, 11:59pm UTC](https://www.ruby-forum.com/t/how-can-i-ask-to-which-module-a-method-belongs-to/67197/3 "2006-09-01T23:59:44Z")
> 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 Sexy! 🙂 IMO something like this would make a nice addition to the core library. Jumping through hoops for introspection is no fun. (At least this one doesn’t involve any string parsing.) Note that the Method#inspect method gives you this same information in string form: irb(main):001:0\> “”.method( :== ) =\> #\ irb(main):002:0\> String.instance\_method( :== ) =\> #\ irb(main):003:0\> “”.method( :id ) =\> #\ irb(main):004:0\> String.instance\_method( :id ) =\> #\ irb(main):005:0\> “”.method( :map ) =\> #\ irb(main):006:0\> String.instance\_method( :map ) =\> #\ Less or more reliable to use this with string parsing? Perhaps slightly more, if only to be sure that the method resolution order is properly followed. ---
**Author:** ![dk3qu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/d2c977/32.png) [@dk3qu](https://www.ruby-forum.com/u/dk3qu)\ **Post date:** [September 2, 2006, 11:05pm UTC](https://www.ruby-forum.com/t/how-can-i-ask-to-which-module-a-method-belongs-to/67197/4 "2006-09-02T23:05:11Z")
On 9/1/06, Phrogz [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > =\> #\ > more, if only to be sure that the method resolution order is properly > followed. Well although the ri documentation for Module#included\_modules doesn’t say wo in so many words, it does in fact produce the list in the right order. The way an included module is implemented is that a ‘hidden’ proxy class is inserted between the class which includes the module, and it’s superclass. It’s hidden because it’s marked as being a T\_ICLASS. The included\_modules C code just walks the chain from the super class and the superclass of the class, listing any T\_ICLASSes that it finds. ## Since this is the way that method lookup works, it’s exactly the right order. Rick DeNatale My blog on Ruby [http://talklikeaduck.denhaven2.com/](http://talklikeaduck.denhaven2.com/) IPMS/USA Region 12 Coordinator [http://ipmsr12.denhaven2.com/](http://ipmsr12.denhaven2.com/) Visit the Project Mercury Wiki Site [http://www.mercuryspacecraft.com/](http://www.mercuryspacecraft.com/)