From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Discriminant of a limited type object
Date: Thu, 1 Mar 2018 09:43:03 +0100
Date: 2018-03-01T09:43:03+01:00 [thread overview]
Message-ID: <p78een$1jfi$1@gioia.aioe.org> (raw)
In-Reply-To: p77csu$4i8$1@franka.jacob-sparre.dk
On 01/03/2018 00:10, Randy Brukardt wrote:
> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message
> news:p74nge$1oto$1@gioia.aioe.org...
> ...
>> The problem is passing state between calls to the function. The code in
>> mind is a loop over array elements. The loop body gutted and its parts
>> moved into the function.
>>
>> A : T (1..N);
>> begin
>> for Index in A'Range loop
>> do-init of A (Index)
>> end loop;
>>
>> |
>> V
>>
>> Index : Positive := 1;
>> function F return Element is
>> begin
>> Index := Index + 1;
>> return do-init of A (Index - 1);
>> end F;
>> A : T (1..N) := (others => F)
>>
>> Quite ugly. In the end I decided to flatten record variants and make the
>> discriminant a plain record member. The memory loss is not big enough to
>> justify the code above.
>
> Ada 2020 has you covered:
>
> function F(Index : Natural) return Element is
> begin
> return do-init of A (Index - 1);
> end F;
> A : T (1..N) := (for I in 1 .. N => F(I));
>
> Note the new iterator choice in the aggregate.
Definitely less ugly than recursion. But does this "loop" guarantee that
F will be called in the order? Say we wanted read an array of limited
elements from stream:
function Read (Stream : not null access Root_Stream_Type'Class)
return Element is
begin
return Result : Element (Length => Read (Stream)) do
Read (Stream.all, Result.Text);
end return;
end F;
A : T (1..N) := (for I in T'Range => Read (File'Access));
--
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de
next prev parent reply other threads:[~2018-03-01 8:43 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-27 17:54 Discriminant of a limited type object Dmitry A. Kazakov
2018-02-27 22:20 ` Randy Brukardt
2018-02-27 22:53 ` Dmitry A. Kazakov
2018-02-28 6:36 ` J-P. Rosen
2018-02-28 8:42 ` Dmitry A. Kazakov
2018-02-28 9:07 ` J-P. Rosen
2018-02-28 17:16 ` Jeffrey R. Carter
2018-02-28 23:10 ` Randy Brukardt
2018-03-01 8:43 ` Dmitry A. Kazakov [this message]
2018-03-01 22:00 ` Randy Brukardt
2018-03-02 10:30 ` Dmitry A. Kazakov
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