[fpc-pascal] generic proc inference

[Ryan Joseph]

Thanks for testing. I don’t have access to Delphi so I need help to make it Delphi compatible.

> On Oct 6, 2019, at 2:06 PM, Mattias Gaertner via fpc-pascal <fpc-pascal at lists.freepascal.org> wrote:
> 
> 1.
> FPC allows default params, Delphi does not. Nice.
> I see no tests for this though, so maybe this was not on purpose?

Probably an oversight if you can believe it. I’ll test that.

> 
> 2.
> DoThis(1,200) gives range check warning instead of error. A warning
> means there are some rare cases, where this code is correct. Is this a
> todo or do you see a useful case?


Which test? Please post a sample.

> 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.

This sounds familiar from C# also. Is that the problem case? I feel like we already went over this but it was months ago..

generic procedure DoThis<T>(msg: T);
begin
	writeln('DoThis$1#1:',msg);
end;

generic procedure DoThis<T>(msg: T; param1: T);
begin
	writeln('DoThis$1#2:',msg,' ',param1);
end;


> 
> 4.
> Why does timpfuncspez6 fail?
> It works in Delphi.
> The comment has an explanation, which looks wrong to me:
> 
> generic procedure DoThis<T,U>(msg: T; param1: U; param2: TObject);
> begin
> end;
> 
> begin
>        DoThis('aa', 'aa', TObject.Create);
>        // wil be specialized as DoThis(msg: integer; param1: TObject;
> param2: TObject)
>        // so we expect an incompatible type error
>        DoThis(1, 1, TObject.Create);
> end.

That doesn’t make sense to me either so I need to study it. Both should fail actually as I designed it (for now).

How does Delphi implicitly specialize this?

Regards,
	Ryan Joseph