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From: Niklas Holsti <niklas.holsti@tidorum.invalid>
Newsgroups: comp.lang.ada
Subject: Re: Ada requires too much typing!
Date: Thu, 10 Jun 2010 23:09:53 +0300
Organization: Tidorum Ltd
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Date: 2010-06-10T23:09:53+03:00
List-Id: <comp.lang.ada>

Simon Wright wrote:
> Georg Bauhaus <rm.dash-bauhaus@futureapps.de> writes:
> 
>> with Ada.Text_IO;  use Ada.Text_IO;
>>
>> procedure Sttc is
>>
>>    type T is range 0 .. 10;
>>
>>    procedure A is
>>       package P is
>>          V: T;
>          pragma Export (C, V, "naughty_v");      --<<<<<<<<<<
>>       end P;
>>    begin
>>       if P.V'Valid then
>>          P.V := P.V + 1;
>>       else
>>          P.V := T'First;
>>       end if;
>>       Put_Line (T'Image(P.V));
>>    end A;
>>
>>    procedure Ovrwrt_Stk  is
>>       X : T;
>>    begin
>>       X := T'First;
>>    end Ovrwrt_Stk;
>>
>> begin
>>    A; Ovrwrt_Stk; A; Ovrwrt_Stk; A; Ovrwrt_Stk; A;
>> end Sttc;
>>
>> $ ./sttc
>>  0
>>  1
>>  1
>>  1
>> $
>>
>> Phew. Back to normal.
> 
> $ gnatmake sttc -f -gnatVa
> gcc -c -gnatVa sttc.adb
> sttc.adb:10:28: warning: "V" has been made static as a result of Export
> sttc.adb:10:28: warning: this usage is non-standard and non-portable
> gnatbind -x sttc.ali
> gnatlink sttc.ali
> $ ./sttc
>  1
>  2
>  3
>  4
> 
> (this is a GNAT-ism, of course, and is present in at least GNAT Pro
> 3.16a1 for powerpc-wrs-vxworks and GCC 4.5.0 for x86_64-apple-darwin10).

It is also present in GNAT 4.3 in debian lenny.

You can even initialize V in its declaration, for example as V : T : = 
T'First, and GNAT will make this initialization happen once. No need for 
the unreliable trickery with 'Valid.

Interesting curio to know, but as for using it... nah.

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
       .      @       .