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From: =?utf-8?Q?Yannick_Duch=C3=AAne_=28Hibou57?=
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Newsgroups: comp.lang.ada
Subject: Re:
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Date: Wed, 24 Oct 2012 18:40:58 +0200
Organization: Ada @ Home
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Date: 2012-10-24T18:40:58+02:00
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Le Fri, 19 Oct 2012 01:44:29 +0200, Yannick Duch=C3=AAne (Hibou57)  =

<yannick_duchene@yahoo.fr> a =C3=A9crit:

> Is this GNAT doing macro=E2=80=91expansion for generics, or me missing=
 some  =

> trick of Ada 2012?
>

Really has issue with DbC (Design by Contract). Here is another bug I  =

encountered. Note: I know source snippets exposing bugs are boring thing=
s  =

to read, but I will post it anyway, if ever that can be of interest for =
 =

someone. I will post two or three other cases, around the same snippet. =
 =

Obviously, this does not stand for the reliable, it was simplified down =
as  =

much as possible, as the purpose is two talk about the issue.

     -- bug1.adb

     procedure Bug1 is

        package P is

           type A_Type  is mod 256;
           type I_Type  is range 0 .. 4_000;
           type S_Type is array (I_Type range <>) of A_Type;

           type T (I, J : I_Type)
              is record
                 S : S_Type (1 .. J);
                 K : I_Type :=3D 1;
              end record
              with
                 Predicate =3D>
                    (T.K <=3D T.I) and
                    (T.I <=3D T.J);

        end P;

        package body P is
           -- Useless, but see below,
           -- in the second comments
           -- about a variation on the bug.
        end P;

        E : P.T (I =3D> 2_000, J =3D> 2_006);

     begin
        null;
     end Bug1;


## First bug

Compiled with GNAT 4.6, then executed, I get this:

     raised CONSTRAINT_ERROR : bug1.adb:16 invalid data

While `K` which is (or should) be initialized to 1, is really (or should=
)  =

lower or equal to `I`, which is 2 000.


## Variation

Interesting variation: remove the useless package body given to `P`. Now=
,  =

compiling fails, with this error:

     bug1.adb:16: operator for type "I_Type" defined at line 6 is not  =

directly visible

So it says operators of `I_Type` are not visible from the location of th=
e  =

expression `(T.K <=3D T.I)`; that's obviously buggy.

The latter is similar to the one of the first post. Surprisingly, it  =

depends on the presence of absence of th useless package body.

Another variation, exposing two other bugs (if my mind is right), to com=
e  =

later (just the time to me to simplify it down).


-- =

=E2=80=9CSyntactic sugar causes cancer of the semi-colons.=E2=80=9D [1]
=E2=80=9CStructured Programming supports the law of the excluded muddle.=
=E2=80=9D [1]
[1]: Epigrams on Programming =E2=80=94 Alan J. =E2=80=94 P. Yale Univers=
ity