From: "Peña, Botp" <botp@...>
Date: 2008-09-03T13:18:48+09:00
Subject: Re: How can I prevent include one module multi-times?

From: Zhao Yi [mailto:youhaodeyi@gmail.com] 
# I am looking for a method to check whether this module has been
# included. Does Ruby have this feature?

you can query the class/module thru #included_modules

eg,

> class C
> end
=> nil

> C.included_modules
=> [Kernel]

> module M
> end
=> nil

> class C
> include M
> end
=> C

> C.included_modules
=> [M, Kernel]


or if you want to query the whole program space, search the ObjectSpace

eg, 

> ObjectSpace.each_object(Module).select{|m| m.class.name == "Module"}

=> [IRB, Exception2MessageMapper, Marshal, ObjectSpace, GC, Math, Process::Sys, Process::GID, Process::UID, Process, Signal, File::Constants, FileTest, Errno, Precision, Enumerable, Comparable, Kernel, Readline, RubyToken, IRB::Notifier, M, IRB::MethodExtender, IRB::ContextExtender, IRB::ExtendCommandBundle]

kind regards -botp