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Newsgroups: comp.lang.ada
Date: Mon, 9 Apr 2018 16:43:31 -0700 (PDT)
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Subject: Re: no, it can't be,
 there's no "with procedure instance_of_generic_procedure
 is new generic_procedure;" ? Impossible !
From: Shark8 <onewingedshark@gmail.com>
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Xref: reader02.eternal-september.org comp.lang.ada:51427
Date: 2018-04-09T16:43:31-07:00
List-Id: <comp.lang.ada>

On Sunday, April 8, 2018 at 12:50:15 AM UTC-6, J-P. Rosen wrote:
> Le 08/04/2018 =C3=A0 02:32, Mehdi Saada a =C3=A9crit=C2=A0:
> > I just realized one can't do that:
> >=20
> > generic
> > with procedure instance_of_generic_procedure is new generic_procedure;
> > ...
> Of course - because it would be useless. The only thing you know from
> the specification of a generic subprogram is its profile, and you can
> import any procedure with an appropriate profile. While restrict to
> those that are in addition an instantiation of a given generic?

The idea behind my proposal for automatic/default instantiation was address=
ing this, as well as allowing the formal parameters to direct the implicit =
instantiation.

GENERIC
  TYPE Parameter_Type IS (<>);
PROCEDURE Generic_Swap( A, B : Parameter_Type );
PROCEDURE Generic_Swap( A, B : Parameter_Type ) IS
  C : Constant Parameter_Type:=3D A;
BEGIN
  A:=3D B;
  B:=3D C;
END Generic_Swap;

GENERIC
  TYPE Something IS (<>);
  USE PROCEDURE Swap IS NEW Generic_Swap( Parameter_Type =3D> Something );
PACKAGE Example IS
--...
END Example;

Which would allow a more uniform syntax, which is what this seems to be abo=
ut, as well as allow Example.Swap to be implicitly instantiated the instant=
iation of Example.

> You have been mistaken by the case of packages. While it is easy to
> define the matching of subprograms, the matching of packages would be
> almost impossible to define - unless the package in an instantiation of
> a generic, in which case it obviously matches the generic.
>=20
> When Ada95 was designed, there was a demand for passing packages the
> same way as subprograms (already present in Ada83). It appeared that
> this was possible only for packages that were built from the same
> generic. There is no such problem with subprograms.

There was an extension in the iAPX 432 of "Package Types" that have an inte=
resting correlation to this demand, IMO -- if you want to kno more, here's =
the manual:  http://bitsavers.informatik.uni-stuttgart.de/components/intel/=
iAPX_432/172283-001_Reference_Manual_for_the_Intel_432_Extensions_to_Ada_De=
c81.pdf