From: James Edward Gray II <james@...>
Date: 2007-03-02T11:45:47+09:00
Subject: Re: Duck Typing  Hash-Like Objects

On Mar 1, 2007, at 8:26 PM, dblack@wobblini.net wrote:

> Hi --
>
> On Fri, 2 Mar 2007, Gary Wright wrote:
>
>> On Mar 1, 2007, at 7:38 PM, James Edward Gray II wrote:
>>> You're still type checking, you're just doing it in a more  
>>> fragile way. If you want to type check, use the class, I say.
>>
>> Yet if I test for (Hash == mystery_obj) that would not
>> allow someone to pass an RBTree object instead, which I think
>> is a very reasonable thing to allow and works just fine if
>> I only use #fetch.
>
> I had the impression James was talking about the Integer and String
> methods, though then again those aren't actually the classes.  So I'm
> not sure what he meant :-)

I was probably just babbling, not making sense.  I do that.

> But I don't think it was just to test class membership, since that  
> manifestly doesn't help in the kind of situation you're describing.

Yeah, you're right.  I was feeling that this is just an attempt to  
sidestep type checking by inventing a clever new type checking  
system.  It's really just trying to provide a flexible interface though.

Given that, I'm changing my answer.

This is a documentation problem.  As long as the documentation tells  
me your method needs a put_stuff_in() and a pull_stuff_out() to work,  
tells me what they will be passed, and *doesn't* type check, you  
support ALL data structures.  I can always wrap Hash, RBTree,  
Integer, JamesCustomDataVoid, or whatever in a trivial class  
implementing those calls.

Am I making sense yet, or do I just need to go to sleep now?

James Edward Gray II