Re: Ada 2005 box (<>) rules in default values

["Björn Persson" <spam-away@nowhere.nil>]

Alex R. Mosteo wrote:
> My understanding is that you use the <> value to denote the default 
> value of a field in, for example a (limited or not) record:
> 
> Blah : constant Thing :=
>      (First_Component  => 3,
>          Second_Component => 4,
>          others => <>);
> 
> This actually compiles in GNAT GAP/GPL, but there's a thing happening 
> that I don't know if it's that it isn't still completely implemented in 
> Gnat, or is the expected behavior.
> 
> Say, for example, that Thing above is declared like:
> 
> type Thing is record
>    First_Component  : Integer;
>    Second_Component : Integer;
>    Third_Component  : Integer := 5;
> end record;
> 
> I'm finding that if I use the box as in the first example above, the 
> third component will not receive its default value from the type 
> definition (5), but will be uninitialized.

This appears to be corrected in GCC 4.0.2 on Gnu/Linux, as it passes the 
test below. Alex, could you please compile this program and verify that 
it triggers the bug in your environment? If not, you might want to post 
a compilable test case that does display the error.

with Ada.Text_IO; use Ada.Text_IO;

procedure Uninitialized_Field_2005 is

    type Thing is record
       First_Component  : Integer;
       Second_Component : Integer;
       Third_Component  : Integer := 5;
    end record;

    Blah : constant Thing :=
      (First_Component  => 3,
       Second_Component => 4,
       others => <>);

begin
    if Blah.Third_Component = 5 then
       Put("Passed");
    else
       Put("Failed");
    end if;
    Put_Line(": Blah.Third_Component = " &
             Integer'Image(Blah.Third_Component));
end Uninitialized_Field_2005;

$ gnatmake -gnat05 uninitialized_field_2005.adb
gcc -c -gnat05 uninitialized_field_2005.adb
gnatbind -x uninitialized_field_2005.ali
gnatlink uninitialized_field_2005.ali
$ ./uninitialized_field_2005
Passed: Blah.Third_Component =  5

-- 
Bj�rn Persson                              PGP key A88682FD
                    omb jor ers @sv ge.
                    r o.b n.p son eri nu