Randy and Tuck,
first of all, I have to apologize for pestering you with this mail. It
was never meant to be sent. I wrote it with the intention to send it and
collected the RM paragraphs, but the more I did I saw that I wasn't
ready. So I wanted to quit and pressed the wrong button.
I thought about immediately sending a second mail saying "please ignore"
- but then: what I writ I writ!
So I made a long pause before I now come back to this. Apology again for
answering so late. And thank you for your patience.
/Randy: How do YOU want this to work?? Explain your answer./
In effect, I had expected something like what GNAT did, a kind of
aggregate, but without the discriminants that do not occur in an
aggregate. So I tried to understand what the RM has to say... (not a
moderate task)
I've read the complete AIs about the new Image. (There is a remark that
perhaps later a matching Value could be defined. I guess this idea has
been dropped. How could this be done with Image having components not
available in the aggregate.)
I readRM 4.10(7/5) that the parent image should be given, which GNAT did
not do (CE 2021; perhaps this has changed meanwhile) because it used the
actual discriminant names.[This is not a bug report.]
I see there are conflicting aims: Using extension aggregates when
Put_Image is defined for an ancestor (which might have different
discriminants), else using the actual names. I gather that Tuck feels
some sympathy for using actual names!
So in effect the current solution for untagged records looks OK
(replacing discrimininants instead of inheriting them seems like nonsense).
*What I do not understand is RM 4.10(17/5, 18/5) talking about the
default implementation of T'Write. T'Write does not include
discriminants except when they have defaults, which they do not have
here*(yet GNAT outputs them)*. An image without discriminants seems like
utter nonsense to me *- which is what GNAT creates for Image with tagged
derived types under certain conditions*! Is this really the intention?
See below:
*
-----------------------
with Ada.Text_IO;
use Ada.Text_IO;
with Interfaces;
use Interfaces;
procedure Sequence is
type T0 (D0: Integer_8) is tagged record
K0: Integer_8;
end record;
type T1 is new T0 (D0 => -1) with record
K1: Integer_8;
end record;
procedure P0 is
-- D0 K0
X: T0 := ( 1, -1);
begin
Put_Line ("P0");
Put_Line ("==");
Put_Line (X'Image);
New_Line;
end P0;
procedure P1 is
-- D0 K0 K1
X: T1 := (-1, -2, 8); -- D0 must be -1
begin
Put_Line ("P1");
Put_Line ("==");
Put_Line (X'Image);
New_Line;
end P1;
begin
P0;
P1;
end Sequence;
-----------------------
P0
==
(D0 => 1,
K0 => -1)
P1
==
(K0 => -2,
K1 => 8)
