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From: "Matthew Heaney" <mheaney@on2.com>
Newsgroups: comp.lang.ada
Subject: Re: GCC 4.0 Ada.Containers Cursor danger.
Date: 8 Jul 2005 07:52:21 -0700
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Date: 2005-07-08T07:52:21-07:00
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Dmitry A. Kazakov wrote:
> On Fri, 08 Jul 2005 13:15:26 GMT, Matthew Heaney wrote:
>
> But sets and maps are unordered containers.

This is silly.  We are talking about the Ada 2005 standard container
library.  In that library, of course sets and maps *are* ordered.


> > since then there would be no way to find anything without a linear search.
>
> Why somebody might wish such thing is another question.

Which is exactly why they're not part of the standard library!


> > An iterator (either passive or active) simply enumerates elements in
> > their order as specified by the type of container they're in (either
> > sort order or bucket order).
>
> "Their order" is the problem. Depending on its definition the order may
> vary in different ways when the container is mutable.

No.  You're not allowed to change the key (which determimes the order)
in any way that would violate the container abstraction.  "Mutability"
is always restricted, such that only bengin changes are allowed.


> What is the common
> denominator across all container types? There seems to be none.

Vectors and lists are "sequence" containers, that allow you to
explicitly specify the position.

Sets and maps are "associative" container, that positions elements in
key order.  (A sorted order for "ordered" containers, and a hash order
for "hashed" containers.)

All containers have a consistent mechanism for iterating over elements.