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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: how to copy complete column (or row) of matrix to another?
Date: Mon, 2 Oct 2017 18:08:57 -0500
Organization: JSA Research & Innovation
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Xref: news.eternal-september.org comp.lang.ada:48295
Date: 2017-10-02T18:08:57-05:00
List-Id: <comp.lang.ada>

"Lucretia" <laguest9000@googlemail.com> wrote in message 
news:e7eb0977-c449-4d52-8010-72df7c261e0f@googlegroups.com...
>I agree that multi-dimensional array slices should be supported. One
>of the tenet's of Ada is to leave the implementation of things up to the
>compiler, because it knows how best to do it, e.g. parameter passing.
>
>I asked about it here, 
>https://groups.google.com/d/msg/comp.lang.ada/L9XiRrjm3B0/cXfKlQ9-AwAJ
>and the response was, it's not going to happen due to a slice being a name 
>as Randy mentions,
>but it's not a request to speed up the assignment, it's just syntactic 
>sugar to aid readability,
>another of Ada's tenets.

Sigh.

The problem is that supporting that would slow down ALL array assignments to 
parameters, regardless of whether or not the 2-d slices are used. Every such 
assignment would have to be element at a time, because there would be no way 
to determine (within the subprogram) whether or not some slices were used 
that makes the array non-contiguous.

It also would make array indexing operations on such parameters much more 
expensive, for the same reason.

Use of matrixes is thought to be common enough that such a performance hit 
(on code *not* using slices) is unacceptable. This is known as a 
"distributed overhead", where the existence of a feature makes code that 
doesn't use it more expensive.

                                   Randy.