* Declaring private packages to instantiate generics?
@ 2012-05-16 14:21 Markus Schöpflin
2012-05-16 14:36 ` Adam Beneschan
0 siblings, 1 reply; 7+ messages in thread
From: Markus Schöpflin @ 2012-05-16 14:21 UTC (permalink / raw)
I just found myself wanting to write the following code, which Gnat doesn't like:
---%<---
package FOO is
procedure P;
end FOO;
package body FOO is
package BAR is new SOME_GENERIC_PACKAGE;
procedure P is new BAR.P;
end FOO;
--->%---
Can I somehow provide the body of P without writing a procedure which just
forwards to an instantiation of BAR.P, IOW without having to write:
---%<---
package body FOO is
package BAR is new SOME_GENERIC_PACKAGE;
procedure BAR_P is new BAR.P;
procedure P is begin BAR_P; end;
end FOO;
--->%---
Regards,
Markus
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: Declaring private packages to instantiate generics?
2012-05-16 14:21 Declaring private packages to instantiate generics? Markus Schöpflin
@ 2012-05-16 14:36 ` Adam Beneschan
2012-05-16 14:45 ` Markus Schöpflin
2012-05-17 3:37 ` Adam Beneschan
0 siblings, 2 replies; 7+ messages in thread
From: Adam Beneschan @ 2012-05-16 14:36 UTC (permalink / raw)
On Wednesday, May 16, 2012 7:21:24 AM UTC-7, Markus Schöpflin wrote:
> I just found myself wanting to write the following code, which Gnat doesn't like:
>
> ---%<---
> package FOO is
> procedure P;
> end FOO;
>
> package body FOO is
> package BAR is new SOME_GENERIC_PACKAGE;
> procedure P is new BAR.P;
> end FOO;
> --->%---
>
> Can I somehow provide the body of P without writing a procedure which just
> forwards to an instantiation of BAR.P, IOW without having to write:
>
> ---%<---
> package body FOO is
> package BAR is new SOME_GENERIC_PACKAGE;
> procedure BAR_P is new BAR.P;
> procedure P is begin BAR_P; end;
> end FOO;
> --->%---
>
> Regards,
> Markus
You can change the last to
procedure P renames BAR_P;
But that's the best you can do. If you have an incomplete declaration (i.e. the declaration of P in the *spec* of FOO), you can't complete it with a generic instantiation---that's the rule. (I think he reason is that a generic instantiation is equivalent to a declaration of the instance followed by the body of the instance, and doing that here would mean you're declaring P twice, which isn't allowed. It can be argued that the language rules should be relaxed in this case, since it's tripped up more than one person, and offhand I don't see any complications that would arise if it were allowed.)
-- Adam
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: Declaring private packages to instantiate generics?
2012-05-16 14:36 ` Adam Beneschan
@ 2012-05-16 14:45 ` Markus Schöpflin
2012-05-17 1:24 ` Shark8
2012-05-17 3:37 ` Adam Beneschan
1 sibling, 1 reply; 7+ messages in thread
From: Markus Schöpflin @ 2012-05-16 14:45 UTC (permalink / raw)
Am 16.05.2012 16:36, schrieb Adam Beneschan:
[...]
>> ---%<---
>> package body FOO is
>> package BAR is new SOME_GENERIC_PACKAGE;
>> procedure BAR_P is new BAR.P;
>> procedure P is begin BAR_P; end;
>> end FOO;
>> --->%---
>>
>> Regards,
>> Markus
>
> You can change the last to
>
> procedure P renames BAR_P;
Thanks for your answer. Not as nice as I had hoped, but basically what I was
looking for.
Markus
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: Declaring private packages to instantiate generics?
2012-05-16 14:45 ` Markus Schöpflin
@ 2012-05-17 1:24 ` Shark8
0 siblings, 0 replies; 7+ messages in thread
From: Shark8 @ 2012-05-17 1:24 UTC (permalink / raw)
On Wednesday, May 16, 2012 9:45:20 AM UTC-5, Markus Schöpflin wrote:
> Am 16.05.2012 16:36, schrieb Adam Beneschan:
>
> [...]
>
> >> ---%<---
> >> package body FOO is
> >> package BAR is new SOME_GENERIC_PACKAGE;
> >> procedure BAR_P is new BAR.P;
> >> procedure P is begin BAR_P; end;
> >> end FOO;
> >> --->%---
> >>
> >> Regards,
> >> Markus
> >
> > You can change the last to
> >
> > procedure P renames BAR_P;
>
> Thanks for your answer. Not as nice as I had hoped, but basically what I was
> looking for.
>
> Markus
Why is using RENAMES not nice?
It seems that the only difference between using RENAMES and what you showed (procedure P is new BAR.P;) is the syntax.
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: Declaring private packages to instantiate generics?
2012-05-16 14:36 ` Adam Beneschan
2012-05-16 14:45 ` Markus Schöpflin
@ 2012-05-17 3:37 ` Adam Beneschan
2012-05-21 8:06 ` Markus Schöpflin
1 sibling, 1 reply; 7+ messages in thread
From: Adam Beneschan @ 2012-05-17 3:37 UTC (permalink / raw)
On Wednesday, May 16, 2012 7:36:27 AM UTC-7, Adam Beneschan wrote:
> > package FOO is
> > procedure P;
> > end FOO;
> >
> > package body FOO is
> > package BAR is new SOME_GENERIC_PACKAGE;
> > procedure P is new BAR.P;
> > end FOO;
> > --->%---
> >
> > Can I somehow provide the body of P without writing a procedure which just
> > forwards to an instantiation of BAR.P, IOW without having to write:
> >
> > ---%<---
> > package body FOO is
> > package BAR is new SOME_GENERIC_PACKAGE;
> > procedure BAR_P is new BAR.P;
> > procedure P is begin BAR_P; end;
> > end FOO;
> > --->%---
> >
> > Regards,
> > Markus
>
> You can change the last to
>
> procedure P renames BAR_P;
>
> But that's the best you can do. If you have an incomplete declaration (i.e. the declaration of P in the *spec* of FOO), you can't complete it with a generic instantiation---that's the rule. (I think he reason is that a generic instantiation is equivalent to a declaration of the instance followed by the body of the instance, and doing that here would mean you're declaring P twice, which isn't allowed. It can be argued that the language rules should be relaxed in this case, since it's tripped up more than one person, and offhand I don't see any complications that would arise if it were allowed.)
I just got reminded by Tucker Taft that there's a problem if P has parameters. The parameters aren't listed in a generic_instantiation:
package FOO is
procedure P (Param : in Integer; Param2 : out Integer);
end FOO;
package body FOO is
package BAR is new SOME_GENERIC_PACKAGE;
procedure P is new BAR.P;
end FOO;
This makes it less clear to the eye that the second P completes the first one. (This would especially be a problem if there is more than one P with different parameter profiles in the specification.) This makes it clearer:
package FOO is
procedure P (Param : in Integer; Param2 : out Integer);
end FOO;
package body FOO is
package BAR is new SOME_GENERIC_PACKAGE;
procedure New_P is new BAR.P;
procedure P (Param : in Integer; Param2 : out Integer)
renames New_P;
end FOO;
So there's a good reason why the rules are the way they are.
-- Adam
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: Declaring private packages to instantiate generics?
2012-05-17 3:37 ` Adam Beneschan
@ 2012-05-21 8:06 ` Markus Schöpflin
2012-05-21 15:51 ` Simon Wright
0 siblings, 1 reply; 7+ messages in thread
From: Markus Schöpflin @ 2012-05-21 8:06 UTC (permalink / raw)
Am 17.05.2012 05:37, schrieb Adam Beneschan:
> On Wednesday, May 16, 2012 7:36:27 AM UTC-7, Adam Beneschan wrote:
[...]
> I just got reminded by Tucker Taft that there's a problem if P has
> parameters. The parameters aren't listed in a generic_instantiation:
>
> package FOO is procedure P (Param : in Integer; Param2 : out Integer); end
> FOO;
>
> package body FOO is package BAR is new SOME_GENERIC_PACKAGE; procedure P is
> new BAR.P; end FOO;
>
> This makes it less clear to the eye that the second P completes the first
> one. (This would especially be a problem if there is more than one P with
> different parameter profiles in the specification.) This makes it
> clearer:
>
> package FOO is procedure P (Param : in Integer; Param2 : out Integer); end
> FOO;
>
> package body FOO is package BAR is new SOME_GENERIC_PACKAGE; procedure
> New_P is new BAR.P; procedure P (Param : in Integer; Param2 : out Integer)
> renames New_P; end FOO;
>
> So there's a good reason why the rules are the way they are.
You're right, thanks for the follow-up. And it's even the case in my case, I
have a whole bunch of Ps which are implemented as instantiations of the same
procedure.
Markus
PS: Sorry for rewrapping your part of the mail but my NNTP server started to
complain about lines longer than 79 characters when posting.
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: Declaring private packages to instantiate generics?
2012-05-21 8:06 ` Markus Schöpflin
@ 2012-05-21 15:51 ` Simon Wright
0 siblings, 0 replies; 7+ messages in thread
From: Simon Wright @ 2012-05-21 15:51 UTC (permalink / raw)
Markus Schöpflin <no.spam@spam.spam> writes:
> PS: Sorry for rewrapping your part of the mail but my NNTP server
> started to complain about lines longer than 79 characters when
> posting.
I've done this for a long time as a matter of course. It's particularly
necessary now that Google Groups has stopped doing any line-wrap at all!
(and very easy using Emacs gnus - M-q).
I didn't think it was rude?
^ permalink raw reply [flat|nested] 7+ messages in thread
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2012-05-16 14:21 Declaring private packages to instantiate generics? Markus Schöpflin
2012-05-16 14:36 ` Adam Beneschan
2012-05-16 14:45 ` Markus Schöpflin
2012-05-17 1:24 ` Shark8
2012-05-17 3:37 ` Adam Beneschan
2012-05-21 8:06 ` Markus Schöpflin
2012-05-21 15:51 ` Simon Wright
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