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From: Georg Bauhaus <bauhaus@futureapps.invalid>
Newsgroups: comp.lang.ada
Subject: Re: Pointer to instance of indefinite array?
Date: Wed, 13 Aug 2014 09:47:40 +0200
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Xref: news.eternal-september.org comp.lang.ada:21710
Date: 2014-08-13T09:47:40+02:00
List-Id: <comp.lang.ada>

On 13.08.14 06:31, Per Sandberg wrote:
> procedure main is
>     Test_Array : aliased Element_Array (1 .. 20);
> begin
>     Do_Something_With_Array (In_Array => Test_Array'Unrestricted_Access);
>     --  Use Unrestricted_Access attribute to disable
>     --  accessibility and aliased view checks
> end main;

Since 'Unrestricted_Access is not Ada but a GNAT specific pragma,
and since it is not strictly needed, I think that standard Ada's own
'Unchecked_Acceess should be enough?


procedure Main is
    Test_Array : aliased Element_Array := (1 .. 20 => (1, 2));
    -- declared as an unconstrained type to match the pointer type
begin
    Do_Something_With_Array (In_Array => Test_Array'Unchecked_Access);
    --  Use Unchecked_Access attribute since passing
    --  an object that will be inaccessibility at higher levels
    --  (that of the pointer type)
end Main;

If there is need to use a pointer at all, e.g. when using GNAT and
a really big array and the stack of GNAT's environment task is limited
by the operating system, then one may still pass the dereference
   Test_Array_Ptr.all
without any concerns about copying. So Do_Something_With_Array can
declare just an array type in its profile, not a pointer.

I remember something about the ICC compiler supporting an implementation
specific attribute similar to 'Unrestricted_Access. Is there a significant
advantage in using 'Unrestricted_Access in user programs, perhaps suppression
of more checks so that to something runs a lot faster?