ok, so if I have
    procedure bar(f: IntfFoo);
I can do
    bar(SomeClassInstanceThatImplementsFoo);

makes sense, the interface can be gotten at the time of calling.

Now if I have

  generic MyGen<    P: IntfFoo >

then I can also do
  specialize MyGen<SomeClassInstanceThatImplementsFoo>

is that indented?

Because now if I have in MyGen

    FMyField: P;

and I try to assign an interface to it... Then that can't work.

Of course there are cases where it is the other way round, and may be useful.

------------------
Just trying to find out if that is a feature, or an issue that will eventually be changed?

I don't think so. Sounds like a bug ?

Michael.

SomeClassInstanceThatImplementsFoo is a variable? variables should never be never allowed within , which only allow types and constants.

On Feb 3, 2026 at 9:16:28 PM, Michael Van Canneyt via fpc-devel <

Hairy Pixels wrote

SomeClassInstanceThatImplementsFoo is a variable? variables should never be never allowed within , which only allow types and constants.

Ah, sorry, copy and paste.

Its a var for the function call.

The specrialize should have read
     specialize MyGen<Some__Class__ThatImplementsFoo>

So I have a constrained that wants an interface, but I can specialize with a class.

That should not work when you're defining a type.

Michael.

https://gitlab.com/freepascal.org/fpc/source/-/issues/41604

On Feb 3, 2026 at 10:42:05 PM, Martin Frb via fpc-devel <

wrote: https://gitlab.com/freepascal.org/fpc/source/-/issues/41604

program Project1;
{$Mode objfpc}
{$Interfaces CORBA}
type
  IFoo = interface end;
  TBar = class(TObject, IFoo) end;
  generic MyGen<A: IFoo> = class end;
  TSome = specialize MyGen<TBar>;
begin
end.

ok so I can see the whole thing now and this should compile. TBar implements IFoo and "A" must conform to IFoo so TBar is compatible with "A".

Not really.

Below stops compiling, when you uncomment the specialize.

IFoo has a method Test.

TBar does not have that. Only TBar as IFoo would have it. But it isn't cast to IFoo.

program Project1;
{$Mode objfpc}
{$Interfaces CORBA}
type
   IFoo = interface
     procedure Test;
   end;
   TBar = class(TObject, IFoo)
     procedure BarTest; virtual; abstract;
     procedure IFoo.Test = BarTest;
   end;
   generic MyGen<A: IFoo> = class
     procedure p1(x: A);
   end;
   //TSome = specialize MyGen<TBar>;
procedure MyGen.p1(x: A);
begin
   x.Test
end;
begin
end.