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From: Robert A Duff <bobduff@shell01.TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: Copying rows in a two dimensional array.
Date: Mon, 08 Feb 2010 16:20:29 -0500
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Date: 2010-02-08T16:20:29-05:00
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"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:

> On Mon, 08 Feb 2010 08:15:50 -0500, Robert A Duff wrote:
>
>> Actually, slices are one of the least useful features of Ada.
>> I wouldn't mind (much) if they didn't exist in the first place.
>
> But only if the language provided means to have user-defined ones.

I'm all in favor of allowing users to define their own abstractions,
rather than trying to build-in lots of stuff into the language.

.... Which is
> far from trivial.

It's trivial if you only want slices as R-values.
And anyway, slices as L-values don't really work:

    X : String := "abc";

    X (2..2) := "xxx";

One might expect X = "axxxc", but of course it raises
an exception instead.  You can do that sort of thing in Ada
with unbounded strings -- but then you don't get slice
syntax!

>...You need a lot of related types to describe slices
> themselves and indicator sets (ranges). Plus you have to provide means to
> determine if subarrays overlap in order to implement assignment in a safe
> way. And user-defined assignment itself need to be properly done (syntax,
> referential semantics of function results etc.)

- Bob