Re: bug or feature

[Simon Wright <simon@pushface.org>]

Charly <carl.weierstrass@googlemail.com> writes:

> I found the following strange behavior of gnat-gpl-2014 (ubuntu linux
> amd64) and I wonder, if it is a bug in gnat:
>
> I habe a package Datum_Pkg that defines a tagged type Datum and
> Datum_Vector (using Ada.Conainers.Vectors). In the main program I want
> to iterate over the vector (all irrelevant lines removed):
[...]

> Line 13 compiles without message but in line 17 I get an error message:
>    subtype indication does not match element type
> But this line should be equivalent to line 13 because of the subtype
> definition in line 6.

Looks like a regression.

I tried this compilable version of your code

with Ada.Containers.Vectors;
with Ada.Text_IO;
procedure Datum is

   package Datum_Pkg is
      type Datum is tagged record
         V : Integer;
      end record;
      function Image (This : Datum) return String is (This.V'Img);
      package Datum_Vectors
        is new Ada.Containers.Vectors (Index_Type   => Positive,
                                       Element_Type => Datum);
      type Datum_Array is array (Positive range 1 .. 10) of Datum;
   end Datum_Pkg;

   subtype Datum is Datum_Pkg.Datum;
   subtype Datum_Vector is Datum_Pkg.Datum_Vectors.Vector;
--   subtype Datum_Vector is Datum_Pkg.Datum_Array;

   D_Vec : Datum_Vector;

begin

   for Dat : Datum_Pkg.Datum of D_Vec loop
      Ada.Text_IO.Put_Line ("Datum=" & Dat.Image);
   end loop;

   for Dat : Datum of D_Vec loop
      Ada.Text_IO.Put_Line ("Datum=" & Dat.Image);
   end loop;

end Datum;

and it fails as you say with GNAT GPL 2014 and FSF GCC 4.9.0. However,
GNAT GPL 2013 and FSF GCC 4.8.1 are both happy.

Not that that would mean it's a regression, necessarily, but if you swap
the definition of subtype Datum_Vector to the array version compilation
succeeds.