[fpc-pascal] generic proc inference

[Sven Barth]

Mattias Gaertner <nc-gaertnma at netcologne.de> schrieb am Mo., 7. Okt. 2019,
11:59:

> On Mon, 7 Oct 2019 07:54:51 +0200
> Sven Barth via fpc-pascal <fpc-pascal at lists.freepascal.org> wrote:
>
> > Ryan Joseph <genericptr at gmail.com> schrieb am Mo., 7. Okt. 2019,
> > 00:16:
> >[...]
> > > >>> 3.
> > > >>> timpfuncspez2.pp
> > > >>> DoThis<T>
> > > >>> DoThis<T,U>
> > > >>> Delphi gives an error "Ambiguous call to DoThis". FPC silently
> > > >>> selects the one with only one param. IMO this is dangerous, it
> > > >>> should give an error.
> > > >
> > > > generic function DoThis<T>(a: T): T; overload;
> > > > begin end;
> > > > generic function DoThis<T,U>(a: T): U; overload;
> > > > begin end;
> > > >
> > > > begin
> > > >  DoThis(3); // both fits, should give an error
> > > > end;
> > >
> > > This is debatable I think but I understand why "Ambiguous call to
> > > DoThis” would make sense. I’m pretty sure C# does this also.
> > >
> > > What is the rule then? I’ll have to think about that some more.
> > >
> >
> > There is nothing debatable here. If a generic parameter is not used
> > in the parameter list (cause it's used in the result type (either
> > directly or to specialize something else), only the body of the
> > routine or even not at all), then that routine must not be used for
> > implicit specialization.
>
> Yes, but does that mean to tell the programmer, that he is using these
> overloads the wrong way (as Delphi does), or should the compiler silently
> skip invalid overloads.
> For the sake of don't-point-the-gun-at-my-foot, I would vote for the
> first.
>

I'm also for an error.

However does Delphi pick a suitable non-generic overload  if one exists
aside from the two generic ones?

Regards,
Sven

>
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