From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: array from static predicate on enumerated type
Date: Wed, 17 Mar 2021 08:08:33 +0100 [thread overview]
Message-ID: <s2s9ti$qma$1@gioia.aioe.org> (raw)
In-Reply-To: a173284c-ed52-4de5-8df7-6a83ede65435n@googlegroups.com
On 2021-03-17 05:05, Matt Borchers wrote:
> It feels like an unfinished addition or incomplete feature to actively prevent 'First, 'Last, etc. from returning something reasonable about the sub-type in question. Return SOMETHING, even if it pertains to the parent type, and let the programmer decide how it can be useful to them. Using my LETTERS and CURVED_LETTERS example, I still don't see why the following would be problematic:
>
> A <= LETTERS'First
> K <= LETTERS'Last
> 11 <= LETTERS'Length
> 1 <= LETTERS'Pos(B)
> 10 <= LETTERS'Pos(J)
>
> B <= CURVED_LETTERS'First
> J <= CURVED_LETTERS'Last
> 5 <= CURVED_LETTERS'Length
> 0 <= CURVED_LETTERS'Pos(B)
> 4 <= CURVED_LETTERS'Pos(J)
>
> I didn't address 'Succ and 'Pred, but these also seem reasonable.
Consider this:
function Count (A : LETTERS) return Natural is
Count : Natural := 0;
begin
for I in A'First..A'Last loop
Count := Count + 1;
end loop;
end Count;
How this supposed to be compiled? Note that CURVED_LETTERS is a subtype
of LETTERS. So you can pass CURVED_LETTERS to Count.
Count cannot use LETTERS'First, 'Succ etc in its body, they might be
overridden they are like in CURVED_LETTERS.
In short it must either dispatch on the actual argument or else the
argument must be converted to LETTERS in a way that LETTERS operations
would yield the correct result.
Neither is possible.
--
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de
next prev parent reply other threads:[~2021-03-17 7:08 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-12 20:49 array from static predicate on enumerated type Matt Borchers
2021-03-12 21:22 ` Egil H H
2021-03-12 22:16 ` Jeffrey R. Carter
2021-03-12 22:41 ` Dmitry A. Kazakov
2021-03-13 2:06 ` Matt Borchers
2021-03-13 4:55 ` Randy Brukardt
2021-03-15 14:16 ` Matt Borchers
2021-03-15 17:53 ` Shark8
2021-03-16 6:58 ` Randy Brukardt
2021-03-13 8:04 ` Dmitry A. Kazakov
2021-03-15 14:11 ` Matt Borchers
2021-03-15 17:48 ` Shark8
2021-03-15 20:25 ` Dmitry A. Kazakov
2021-03-16 13:27 ` Shark8
2021-03-16 14:25 ` Dmitry A. Kazakov
2021-03-17 4:05 ` Matt Borchers
2021-03-17 7:08 ` Dmitry A. Kazakov [this message]
2021-03-17 18:44 ` Matt Borchers
2021-03-17 19:41 ` Dmitry A. Kazakov
2021-03-18 1:30 ` Matt Borchers
2021-03-18 8:20 ` Dmitry A. Kazakov
2021-03-19 0:10 ` Matt Borchers
2021-03-19 8:00 ` Dmitry A. Kazakov
2021-03-18 10:15 ` Niklas Holsti
2021-03-18 10:47 ` AdaMagica
2021-03-18 11:26 ` Dmitry A. Kazakov
2021-03-19 0:34 ` Matt Borchers
2021-03-19 0:49 ` Jeffrey R. Carter
2021-03-23 1:07 ` Matt Borchers
2021-03-23 3:43 ` Randy Brukardt
2021-03-22 19:09 ` Niklas Holsti
2021-03-17 15:08 ` Shark8
2021-03-17 19:08 ` Matt Borchers
2021-03-17 20:41 ` Shark8
2021-03-18 1:04 ` Matt Borchers
2021-03-18 14:25 ` Shark8
2021-03-18 23:36 ` Matt Borchers
2022-03-16 0:38 ` Thomas
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