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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Ada.Containers.Vectors - querying multiple elements
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Date: Sat, 7 May 2005 09:17:17 +0200
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Date: 2005-05-07T09:17:14+02:00
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On Sat, 07 May 2005 01:20:21 GMT, Matthew Heaney wrote:

> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:
> 
>> In an imaginary, better Ada there should be unordered, uncountable
>> types which would still allow containers. There would be no way to
>> enumerate elements in such container, but for any given X it would be
>> possible to Is_In (X, C). Even for such weak types there should be
>> empty containers such that Is_In returns false for any X.
> 
> Tell me, Dmitry, how do you intend for predicate Is_In to be
> implemented, if the objects in the container are neither ordered nor
> enumerable?

That's an implementation detail! (:-)) But OK, here are many ways depending
on the concrete case. For example: an unordered, uncountable index is just
a public view. The container is free keep an array indexed by plain
numbers. Objects might be uncountable, but we can count containers instead.
So we attach the list of containers in which an object participates to the
object. Or else we could maintain a global incidence matrix ... and so on
and so far. My point actually was: empty containers and index ranges (sets)
must be!

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de