From: dblack@...
Date: 2006-11-08T12:39:00+09:00
Subject: Re: Can't bind a singleton method to a subclass?

Hi --

On Wed, 8 Nov 2006, ara.t.howard@noaa.gov wrote:

> On Wed, 8 Nov 2006 dblack@wobblini.net wrote:
>
>> The fact that B can call A.class_method is due to the special-casing of
>> singleton classes of Class objects; it's the one case where a given 
>> object
>> can execute singleton methods of another object.  But those singleton
>> methods still belong, unambiguously, to the first object, A.  The reason 
>> B
>> can call them is that A's singleton class serves as the superclass of B's
>> singleton class -- so class_method lies on the method look-up path of B.
>> But class_method is still defined only in A's singleton class.
>
> still, quiet odd that one can do this
>
>>> p B.method(:class_method).unbind
>
> meaning, it's strange that you can 'unbind' from a class something which
> cannot be bound to it and yet must have been for the initial call to 
> 'unbind'
> to succeed - a contradiction.

I think it's not so much that you're unbinding it *from* B, as that
you're grabbing it *through* B.  So, by the time you unbind it, it
doesn't "know" that you got it that way; it's just a Method object,
and it allows itself to be unbound.  I'd say that's a side-effect of
the fact that A's singleton methods can be got at via B at all.

Going the other way, though, it does "know" that you're trying to bind
it to something other than the object in whose singleton class it's
defined.


David

-- 
                   David A. Black | dblack@wobblini.net
Author of "Ruby for Rails"   [1] | Ruby/Rails training & consultancy [3]
DABlog (DAB's Weblog)        [2] | Co-director, Ruby Central, Inc.   [4]
[1] http://www.manning.com/black | [3] http://www.rubypowerandlight.com
[2] http://dablog.rubypal.com    | [4] http://www.rubycentral.org