From: Sean O'Dell <sean@...>
Date: 2004-06-08T01:44:16+09:00
Subject: Re: How to ducktype a Hash?

On Monday 07 June 2004 08:39, Paul Sanchez wrote:
> Richard Kilmer wrote:
> >
> > 2) Sean:  It seems like what you are looking for is to check a method for
> > 'semantic equivalence'...that is, you want to say that the [] and []=
> > methods on an object are semantically equivalent to the [] and []=
> > methods on Hash.  Not that the object is in any way (from and inheritance
> > perspective) related to a Hash, nor does it actually get the behavior of
> > a Hash object's []  and []= methods, but when it comes to those two
> > methods...'quack like a Hash'.  Does that sound right?  If so, the
> > question becomes how to express this kind of semantic equivalence both in
> > the definition of the methods, and the checking with respond_to?
>
> I've been watching this thread and I think you've hit the nail on the
> head.  Sean seems to want semantic equivalence, but is using a syntax
> which is overloaded out of the box.  Duck typing is based on syntax
> matching.  It seems to me that the only way to get semantic equivalence
> without using type cues or explicit testing is to steer clear of
> overloaded operators and methods, so that syntax reflects semantics.
> This is what several others were suggesting when they talked about using
> hash's alternate method names in place [] and []=.

I'm not sure what this means.  I'm not looking for duck typing per se, just a 
way to type check hash-like objects.  The only two things I care about when 
checking for something in this way are that the object responds to a group of 
methods which all take the same number of parameter, and the group of methods 
represent a described interface; that is, a known functionality.  In this 
particular case, the functionality should be that of a hash, or a hash-like 
object.

	Sean O'Dell