From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00
	autolearn=unavailable autolearn_force=no version=3.4.4
Path: 
 eternal-september.org!reader01.eternal-september.org!reader02.eternal-september.org!feeder.eternal-september.org!aioe.org!.POSTED!not-for-mail
From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Discriminant of a limited type object
Date: Tue, 27 Feb 2018 23:53:04 +0100
Organization: Aioe.org NNTP Server
Message-ID: <p74nge$1oto$1@gioia.aioe.org>
References: <p745vr$pma$1@gioia.aioe.org>
 <p74lj6$ls3$1@franka.jacob-sparre.dk>
NNTP-Posting-Host: yZRtMzZmKCYxZ5GHo5ZYiA.user.gioia.aioe.org
Mime-Version: 1.0
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 7bit
X-Complaints-To: abuse@aioe.org
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101
 Thunderbird/52.6.0
Content-Language: en-US
X-Notice: Filtered by postfilter v. 0.8.3
Xref: reader02.eternal-september.org comp.lang.ada:50694
Date: 2018-02-27T23:53:04+01:00
List-Id: <comp.lang.ada>

On 2018-02-27 23:20, Randy Brukardt wrote:
> A defaulted discriminant for a limited type means just that: a default for
> the discriminant if the object is default initialized. It was always a
> mistake for Ada to tie that to mutability, but it doesn't matter for a
> limited type.
> 
> You can initialize an array of limited discriminanted objects with an
> aggregate of function calls (since those are built-in-place), and they can
> all have different discriminant values.

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.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de