From: Glenn Vanderburg <glv@...>
Date: 2003-11-20T08:14:27+09:00
Subject: Re: "stereotyping"

--------------ms080503000103050800080209
Content-Type: text/plain; charset=us-ascii; format=flowed
Content-Transfer-Encoding: 7bit

James Weirich wrote:
 >
> I now think what Sean [wants] is some way of "marking" 
 > a class to indicate that in implements a particular protocol.

and Greg McIntyre wrote:
 >
 > I think this is fascinating stuff! Have there been
 > any suggestions yet, even wild stabs at it?

Other languages with similar object models have wrestled with these same 
issues, often long ago.  Smalltalk, for example, was at one time 
extended with the notion of "explicit protocols".

(I'm no expert on this, and what little I do remember is sketchy.  So 
take the details here with a grain of salt.  But please bear with me.)

An explicit protocol was little more than a list of method selectors 
(what we would call signatures, I suppose).  There was an easy way to 
check whether an object implemented a protocol, and that check was 
essentially a shorthand for looping through those selectors and calling 
"respond_to?" on all of them.  A class could also declare that it 
implemented a protocol, but the point wasn't to *publish* anything; 
rather, the declaration just did the implementation check for you and 
issued a warning if you didn't pass.

The idea was that this would make it easier for method writers to 
validate at an early stage that an object would meet the need, and 
signal an error early rather than later.

Seems like a decent idea, and could be implemented easily in Ruby. 
Except for two things.

First:  the method name syntax in Smalltalk indicates clearly the number 
of parameters the method takes.  That's not true in Ruby, so the 
mechanism in Ruby would either be less useful or more complicated.

Second:  explicit protocols never really caught on in Smalltalk, unless 
I'm mistaken.

My point is:  instead of continuing to go around and around about this, 
I wonder if we could persuade a long-time Smalltalker or two to write up 
something explaining the explicit protocol mechanism in Smalltalk more 
thoroughly and accurately than I have, plus an analysis of why it didn't 
catch on.  If we're going to consider this road, we should certainly 
learn from the experience of those who've gone before us.

Regards,
Glenn Vanderburg

--------------ms080503000103050800080209
Content-Type: application/x-pkcs7-signature; name="smime.p7s"
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="smime.p7s"
Content-Description: S/MIME Cryptographic Signature
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--------------ms080503000103050800080209--