From: Robert Dober <robert.dober@...>
Date: 2007-05-30T20:50:50+09:00
Subject: Re: #respond_to? not working for dynamically generated methods

On 5/30/07, dblack@wobblini.net <dblack@wobblini.net> wrote:
> Hi --
>
> On Wed, 30 May 2007, Maurice Gladwell wrote:
>
> > It seems Object#respond_to doesn't work for dynamically generated
> > methods:
> >
> > SomeRailsModel.respond_to? 'find_by_name' #=> false
> >
> > 1. Is there some way to *really* check if an object will respond to a
> > message, even if it will respond by a dynamically generated method?
> >
> > Right now, Object#respond_to? just doesn't do what it name promises: it
> > doesn't check if an object responds to a message :foo, only if the
> > object has a :foo method defined.
Does not look right though

# vim: sts=2 sw=2 expandtab nu tw=0:


module M
  def m; "m" end
end
class A
  def a; "a" end
end

class B < A
  include M
end

b = B.new
def b.b; "b" end

p B.new.respond_to?(:a)
p B.new.respond_to?(:m)
p B.method_defined?(:a)
p B.method_defined?(:m)
p b.respond_to?(:b)
true
true
true
true
true

looks pretty good to me.
Is Rails fooling around with my beloved Ruby ;) ?
For what concerns intercepted messages for which no methods exist
David has said it all below:...
>
> That's what responding to a method means.  Otherwise, it would be
> meaningless, since you can send any message to any object.
>
> Things like find_by_name are made possible by method_missing, which
> intercepts uninterpretable messages.  It's possible for method_missing
> to generate a new method dynamically, but it doesn't have to (and in
> fact "find_by_name" does not get generated as a method; it just gets
> examined as a string).  Even if it does, there's no way for respond_to
> to figure it out.
>
> Basically, to know what's going to happen dynamically, you have to run
> the program and send the messages.
>
>
> David
>
> --
> Q. What is THE Ruby book for Rails developers?
> A. RUBY FOR RAILS by David A. Black (http://www.manning.com/black)
>     (See what readers are saying!  http://www.rubypal.com/r4rrevs.pdf)
> Q. Where can I get Ruby/Rails on-site training, consulting, coaching?
> A. Ruby Power and Light, LLC (http://www.rubypal.com)
>
>

Cheers
Robert
-- 
You see things; and you say Why?
But I dream things that never were; and I say Why not?
-- George Bernard Shaw