Out parameters and unconstrained variant types

Hello friends,

I would like to do something like:

type Conditional_Result (Exists : Boolean := False) is
record case Exists is
when True =>
Value : Natural;
when False =null;
end record;

procedure Do_Something(x : in Natural; rtn : out Conditional_Result)
is
begin
if x = 0 then
rtn := (Exists =False);
else
rtn := (Exists =True; Value =x + 1);
end if;
end;

procedure Foo is
rtn : Conditional_Result;
begin
Do_Something(0, rtn);
if rtn.Exists then
Put_Line("Yes!");
end if;
Do_Something(1, rtn);
if rtn.Exists then
Put_Line("Yes!");
end if;
end;

ALRM 2005 and Barnes seem to say the procedure Do_Something will know
that rtn in foo is unconstrained and allow both calls to succeed. In
GNAT 2007, the second call fails with a constraint error at the
assignment to rtn. Can you tell me what I'm missing?

Thanks!

Gene wrote:

ALRM 2005 and Barnes seem to say the procedure Do_Something will know
that rtn in foo is unconstrained and allow both calls to succeed.

You can express your expectations in the program by adding

pragma Assert(not rtn'Constrained);


-- Georg