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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Little people supporting Ada, possibly through AdaCore?
Date: Thu, 19 Jul 2012 21:51:05 -0500
Organization: Jacob Sparre Andersen Research & Innovation
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Date: 2012-07-19T21:51:05-05:00
List-Id: <comp.lang.ada>

"Vasiliy Molostov" <molostoff@gmail.com> wrote in message 
news:op.whoz7g1gka8ora@aspire.local...
...
> I suppose that for user an unknown order means no order.

Not really. There are many, many examples of programmers taking advantage of 
a order that a particular implementation has. As Dmitry points out, it's 
important that the interfaces expose as little order as possible.

This is, in fact, the reason that we ultimately decided that Ada shouldn't 
have unordered maps and sets. The implementation would necessarily iterate 
the maps and sets in some order, and it seemed impossible to prevent code 
from depending on that order. Moreover, lookups in a truly unordered map or 
set are expensive (requiring looking at the complete contents of the map or 
set), and there seemed to be no significant performance advantage to the 
unordered forms over the other forrms.

Of course, the iteration order of a hashed map is unknown and should not be 
depended upon, but that doesn't stop people from trying (as in the OP). 
Probably, unordered containers shouldn't allow any iteration, but that's 
obviously limiting.

                                         Randy.