From: Gavin Sinclair <gsinclair@...>
Date: 2004-06-07T02:19:32+09:00
Subject: Re: How to ducktype a Hash?

On Monday, June 7, 2004, 2:42:06 AM, Sean wrote:

> A type would say something like:

> All hashes have a method called each_pair that takes no parameters and calls
> the given block once for each key/value pair the hash contains.

> Now, for brevity, consider that the entire type description for a Hash.  What
> we have now is a "hash type."  The Hash class itself can still change it's
> methods, including its each_pair method, but if it ever strays from the
> description of a hash type, it is no longer a hash type.

> If Hash tagged itself as complying with the "hash type" you could depend on
> certain methods doing certain things and taking a certain number of 
> parameters.

What if a class tags itself as a "hash type" but an instance of it
redefines a method in a way that contradicts that type?

I'm not being alarmist, but your messages have shown a great deal of
concern for knowing that an object does what it advertises.  How do
you see the above scenario, then?

I don't think your idea is a bad one, by the way.

Gavin