* Validity of renamed objects?
@ 2014-04-01 13:04 Jacob Sparre Andersen
2014-04-01 13:44 ` J-P. Rosen
2014-04-01 13:55 ` Markus Schöpflin
0 siblings, 2 replies; 4+ messages in thread
From: Jacob Sparre Andersen @ 2014-04-01 13:04 UTC (permalink / raw)
I've been reading section 8.5.1 in the LRM, and I can't figure out when
the compiler is supposed to check the validity of a renamed object.
An example:
procedure Renaming_1 is
Object : String (1 .. 9) := "dead beef";
Index : Natural := 0;
Renamed : Character renames Object (Index);
begin
Index := (Object'First + Object'Last) / 2;
if Renamed /= ' ' then
raise Program_Error
with "Expected Renamed to match the changed value of Index.";
end if;
end Renaming_1;
1) Should I get a Constraint_Error when Renamed is declared?
2) What will the value of Renamed be after Index has been changed?
Greetings,
Jacob
PS: I know what the version of GNAT I have at hand does, but what it
does is not completely obvious from my reading of the LRM.
--
»But you have to be a bit wary of a ship that collects
snowflakes.« -- Diziet Sma
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: Validity of renamed objects?
2014-04-01 13:04 Validity of renamed objects? Jacob Sparre Andersen
@ 2014-04-01 13:44 ` J-P. Rosen
2014-04-01 13:55 ` Markus Schöpflin
1 sibling, 0 replies; 4+ messages in thread
From: J-P. Rosen @ 2014-04-01 13:44 UTC (permalink / raw)
Le 01/04/2014 15:04, Jacob Sparre Andersen a écrit :
> I've been reading section 8.5.1 in the LRM, and I can't figure out when
> the compiler is supposed to check the validity of a renamed object.
>
> An example:
>
> procedure Renaming_1 is
> Object : String (1 .. 9) := "dead beef";
> Index : Natural := 0;
> Renamed : Character renames Object (Index);
> begin
> Index := (Object'First + Object'Last) / 2;
> if Renamed /= ' ' then
> raise Program_Error
> with "Expected Renamed to match the changed value of Index.";
> end if;
> end Renaming_1;
>
> 1) Should I get a Constraint_Error when Renamed is declared?
Yes
> 2) What will the value of Renamed be after Index has been changed?
>
Assuming Index is 1 (in order to avoid Constraint_Error), Renamed is
unchanged.
The principle is that when you elaborate the renaming declaration, you
evaluate the renamed object, and from then on the renaming identifier
designates that object. It's not a macro!
--
J-P. Rosen
Adalog
2 rue du Docteur Lombard, 92441 Issy-les-Moulineaux CEDEX
Tel: +33 1 45 29 21 52, Fax: +33 1 45 29 25 00
http://www.adalog.fr
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: Validity of renamed objects?
2014-04-01 13:04 Validity of renamed objects? Jacob Sparre Andersen
2014-04-01 13:44 ` J-P. Rosen
@ 2014-04-01 13:55 ` Markus Schöpflin
2014-04-01 18:35 ` Jacob Sparre Andersen
1 sibling, 1 reply; 4+ messages in thread
From: Markus Schöpflin @ 2014-04-01 13:55 UTC (permalink / raw)
Am 01.04.2014 15:04, schrieb Jacob Sparre Andersen:
> I've been reading section 8.5.1 in the LRM, and I can't figure out when
> the compiler is supposed to check the validity of a renamed object.
>
> An example:
>
> procedure Renaming_1 is
> Object : String (1 .. 9) := "dead beef";
> Index : Natural := 0;
> Renamed : Character renames Object (Index);
> begin
> Index := (Object'First + Object'Last) / 2;
> if Renamed /= ' ' then
> raise Program_Error
> with "Expected Renamed to match the changed value of Index.";
> end if;
> end Renaming_1;
>
> 1) Should I get a Constraint_Error when Renamed is declared?
Yes, see 8.5(3).
"Object (Index)" is evaluated when the renaming declaration is elaborated.
Markus
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: Validity of renamed objects?
2014-04-01 13:55 ` Markus Schöpflin
@ 2014-04-01 18:35 ` Jacob Sparre Andersen
0 siblings, 0 replies; 4+ messages in thread
From: Jacob Sparre Andersen @ 2014-04-01 18:35 UTC (permalink / raw)
Markus Schöpflin <no.spam@spam.spam> writes:
> Am 01.04.2014 15:04, schrieb Jacob Sparre Andersen:
>> I've been reading section 8.5.1 in the LRM, and I can't figure out
>> when the compiler is supposed to check the validity of a renamed
>> object.
> Yes, see 8.5(3).
>
> "Object (Index)" is evaluated when the renaming declaration is
> elaborated.
Yes. Reading that paragraph it is quite clear. Thanks! (Also to
Jean-Pierre.)
Greetings,
Jacob
--
"If you think Tuck has said something that is completely
wrong, you are almost certainly missing something :-)"
^ permalink raw reply [flat|nested] 4+ messages in thread
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2014-04-01 13:04 Validity of renamed objects? Jacob Sparre Andersen
2014-04-01 13:44 ` J-P. Rosen
2014-04-01 13:55 ` Markus Schöpflin
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