first_responder.rb

# klass.first_responder(:method) gives you the Module in klass's inheritance chain which will respond to :method.
# klass.all_responders(:method) gives you all of the Modules in klass's inheritance chain which can respond to :method, in order from klass to Kernel.

require 'metaid'

class Object
  def first_responder(method)
    method = method.to_s
    metaclass.ancestors.find do |mod|
      mod.instance_methods(false).include? method
    end
  end
  def all_responders(method)
    method = method.to_s
    metaclass.ancestors.find_all do |mod|
      mod.instance_methods(false).include? method
    end
  end
end