From: dblack@...
Date: 2007-05-30T20:55:39+09:00
Subject: Re: #respond_to? not working for dynamically generated methods

Hi --

On Wed, 30 May 2007, Robert Dober wrote:

> 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 ;) ?

No, it's just using method_missing, which intercepts the
"find_by_name" message.

> For what concerns intercepted messages for which no methods exist
> David has said it all below:...

I'll go along with that :-)


David

-- 
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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)