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Date: Thu, 18 Oct 2007 14:55:25 -0500
From: Robert Fischer <robert@fischerventure.com>
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To: skaller <skaller@users.sourceforge.net>
Cc: Arnaud Spiwack <aspiwack@lix.polytechnique.fr>,
	caml-list@yquem.inria.fr
Subject: Re: [Caml-list] Smells like duck-typing
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X-Spam: no; 0.00; invariants:01 invariants:01 caml-list:01 define:02 defined:02 inheriting:02 derived:05 classes:08 fischer:10 interesting:12 methods:12 methods:12 happens:13 robert:13 robert:13 


> But that never happens with mutators because you cannot
> HAVE any additional invariants. The derived type has
> to have exactly the same set of values as the base,
> in which case you cannot have any new interesting
> methods -- any method you have can always be defined
> in terms of the characteristic methods already in
> the base (assuming the whole public state is accessible
> of course).
>   
This is why you 1) define a base class which has a very loose set of 
invariants or 2) obscure state from inheriting classes.

~~ Robert.