From: Sean O'Dell <sean@...>
Date: 2003-11-20T06:25:32+09:00
Subject: Re: "stereotyping" (was: Re: Strong Typing (Re: Managing metadata about attribute types)

On Wednesday 19 November 2003 01:10 pm, Austin Ziegler wrote:
> On Thu, 20 Nov 2003 04:37:50 +0900, Sean O'Dell wrote:
> > On Wednesday 19 November 2003 11:05 am, Yukihiro Matsumoto wrote:
> >> A class has interface; a class can be used as interface (by set
> >> of its methods); but it should not be checked by kind_of? or
> >> anything based on inheritance, just because it hinders
> >> flexibility of dynamic typing so much; remember StringIO or
> >> tempfile examples.
> >
> > But again, that flexibility is LOST when you have to pass an
> > object to a method that REQUIRES it to behave a certain way. The
> > flexibility is already gone; it wasn't eliminate by a language
> > quirk, it was eliminated by the need of the method being called.
>
> This argument is circular.
>
> > I'm only talking about checking that a certain interface is
> > present. Just for the purpose of providing an informative error
> > message when an object which cannot fulfill the needs of a method
> > is passed. Right now, it just explodes with an ugly message about
> > something that happened deep in the called method. Something more
> > informative would go a LONG way.
>
> Static typing in Ruby carries too high a performance price, because
> *everything* (including class and method definitions) are executed
> at runtime.
>
> Far better to have an interface publication mechanism than static --
> or "strong" typing.

This what I'm advocating.  But for simplicity, the interface descriptions can 
be taken from existing classes and modules.  They're already used for 
inheritance and mix-ins, so it makes sense.  If a class inherits from 
another, you can assume it implements its interface.  The methods of the 
interface are never encoded in any way.  The interface is just a name, a 
declaration.

	Sean O'Dell