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From: Matthew Heaney <matthew_heaney@acm.org>
Subject: Re: Access to aliased string declaration question.
Date: 1999/06/10
Message-ID: <m3aeu8fn4t.fsf@mheaney.ni.net>#1/1
X-Deja-AN: 487836178
References: <375ED457.A85A462B@Boeing.com> <m3ogiofyua.fsf@mheaney.ni.net>
NNTP-Posting-Date: Thu, 10 Jun 1999 01:52:11 PDT
Newsgroups: comp.lang.ada
Date: 1999-06-10T00:00:00+00:00
List-Id: <comp.lang.ada>

On 10 Jun 1999 04:39, Matthew Heaney <matthew_heaney@acm.org> wrote:

> It's not all that bad, either.  Sometimes you can have it both ways by
> declaring a dynamic (or maybe static) access subtype:
> 
>   type String_Access is access all String;
> 
>   S : aliased String (1 .. 10);
> 
> ...
> 
>   declare
>     subtype S_Access is String_Access (S'Range);
>     SA : S_Access := S'Access;
>   begin
> 
> Here we declare a subtype that points only to strings having the bounds
> of object S.  This is a constrained string object, designed by an access
> object whose (base) type is unconstrained.

Actually, you don't even need the subtype mark:

  declare
    SA : String_Access (S'Range) := S'Access;
  begin


> This works even if the bounds are determined at run-time:
> 
>   procedure Op (F, L : Positive) is
> 
>     S : aliased String (F .. L);
> 
>     subtype S_Access is String_Access (F .. L);  -- or S'Range
> 
>     SA : S_Access := S'Access;
> 
>   begin


No subtype mark is needed here either:

  procedure Op (F, L : Positive) is

     S : aliased String (F .. L);

     SA : String_Access (S'Range) := S'Access;

  begin