[fpc-devel] generic forward declaration?

[Michael Van Canneyt]

On Tue, 29 Jul 2025, Martin Frb via fpc-devel wrote:

> Are there? Or is there something else?
>
> The below compiles. No duplicate TBar. Looks like a forward declaration...
>
> program Project1;{$Mode objfpc}
> type
>   generic TBar<A,B> = class; // forward
>
>   generic TBar<A, B> = class
>     F:A;
>     X:B;
>   end;
>
> begin
> end.
>
>
>
> But the next does not compile "Identifier not found TBar" (inside TFoo). 
> Yet the identifier is clearly there.
>
> https://gitlab.com/freepascal.org/fpc/source/-/issues/24097 seems to say 
> it is supported since 2022?
>
> program Project1;
> {$Mode objfpc}
> type
>
>   generic TBar<A,B> = class; // forward
>
>   generic TFoo<A, B> = class
>     F:specialize TBar<A>;

You're missing a type parameter here. 
According to the definition, TBar needs 2 type parameters.

>     X:B;
>   end;
>
>   generic TBar<A, B> = class
>     F:specialize TFoo<A>;

Same here, you're missing a type parameter. TFoo needs 2 type parameters.

if you fix that (I added B in both cases, just to test) it compiles.

Michael.