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From: Jacob Sparre Andersen <sparre@nbi.dk>
Newsgroups: comp.lang.ada
Subject: Re: Is this a bug in my code or the compiler?
Date: Sat, 13 Jun 2015 18:43:18 +0200
Organization: Jacob Sparre Andersen Research & Innovation
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Date: 2015-06-13T18:43:18+02:00
List-Id: <comp.lang.ada>

"J-P. Rosen" <rosen@adalog.fr> writes:

> Le 13/06/2015 15:33, Jacob Sparre Andersen a écrit :
>>   procedure P (A, B : in out T);
>> 
>>    P (C, C);
>> 
>> But I can't get it to complain about a simplified variation of your
>> case.
>> 
>> Maybe there is an AdaControl rule to detect this kind of problem. 
> Of course. It's called Parameter_Aliasing :-)

I tried it without luck on this test case:

% cat bad_style_2.adb
with Ada.Integer_Text_IO,
     Ada.Text_IO;

procedure Bad_Style_2 is
   function F (I : in out Integer) return Character;
   function G (I : in out Integer) return String;

   function F (I : in out Integer) return Character is
   begin
      return R : Character do
         if I < 0 then
            R := '-';
         else
            R := '+';
         end if;

         I := 2 * I;
      end return;
   end F;

   function G (I : in out Integer) return String is
   begin
      return R : constant String := Integer'Image (I) do
         I := I - 1;
      end return;
   end G;

   C : Integer := 3;
begin
   Ada.Text_IO.Put_Line (F (C) & G (C));
   Ada.Integer_Text_IO.Put (C);
end Bad_Style_2;
% adactl -l 'check parameter_aliasing' bad_style_2.adb
%

I.e. no detection of "expression parameter aliasing" (or what we should
call it).  I think it is only slightly harder to detect than plain
parameter aliasing, but I'm not yet quite proficient enough in ASIS to
promise to contribute a new rule to AdaControl.

Greetings,

Jacob
-- 
"It is very easy to get ridiculously confused about the
 tenses of time travel, but most things can be resolved
 by a sufficiently large ego."