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!.POSTED!not-for-mail
From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: why "unconstrained subtype in component declaration" while said
 component given default value ?
Date: Sun, 27 May 2018 08:07:03 +0100
Organization: A noiseless patient Spider
Message-ID: <lyy3g5efvs.fsf@pushface.org>
References: <f9a3c91e-03d0-4053-827b-170ba762dddf@googlegroups.com>
Mime-Version: 1.0
Content-Type: text/plain
Injection-Info: h2725194.stratoserver.net;
 posting-host="72c963eeffe8f0f65beee661c7eaff64";
	logging-data="5326"; mail-complaints-to="abuse@eternal-september.org";
	posting-account="U2FsdGVkX18IdxkF1YSKnNgH/qw/nsGUO8JndTuNavY="
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.3 (darwin)
Cancel-Lock: sha1:7ehEIQ6HMWoBmJJD+AKdaBawxnM=
	sha1:SgdIZ4i3mDGWg1NZicnEAaNf0wc=
Xref: reader02.eternal-september.org comp.lang.ada:52717
Date: 2018-05-27T08:07:03+01:00
List-Id: <comp.lang.ada>

Mehdi Saada <00120260a@gmail.com> writes:

> Also, there's something that would be really cool, and I'm curious why
> it could not be allowed: Why can't we provide a private constrained
> subtype, of an inconstrained private type ?
>
> package III is
>    type A (<>) is private;
>    subtype B is A;  -- should be a constrained subtype
> private
>    function Donne_String (N : Positive) return String;
>    type A (N: Positive) is record
>       II : Integer;
>       Chaine : String(1..N) := Give_String(N);
>    end record;
> end III;

The Booch Components originally had the maximum length of a bounded
container fixed at generic instantiation, which is a very limiting
design. So as to avoid forcing all users to rework, I ended up with, for
example,

generic
   Maximum_Size : Positive;
package BC.Containers.Collections.Bounded is

   type Unconstrained_Collection
     (Maximum_Size : Positive) is new Abstract_Collection with private;

   subtype Collection
      is Unconstrained_Collection (Maximum_Size => Maximum_Size);

[...]

   function "=" (Left, Right : in Unconstrained_Collection) return Boolean;

[...]

   procedure Insert (C : in out Unconstrained_Collection; Elem : Item);
   --  Add the item to the front of the collection.