[fpc-devel] inheritance of interfaces.

[Michael Van Canneyt]

On Mon, 2 Feb 2026, Martin Frb via fpc-devel wrote:

> If I have the below code, I can pass an object that has I1 (TFoo if 
> uncommented) to the test function
>
> I can also pass an inherited interface. "x1: i2"
>
> But I can not pass a call that only has the inherited interface?
>  Error: Class "TFoo" does not implement interface "I1"
>
> Is that intended?

Yes

>
> Since TFoo implement I2, it does also implement I1.

No. The inheritance is just a typing convenience.

When you do an "as interface", then the compiler looks for the UUID of the
interface in a table.

If you define
   TFoo = class(TObject, I2)
only the UUID of I2 is inserted in the table.

but if you define
   TFoo = class(TObject, I1, I2)
then the table will contain both UUIDS and the "as I1" will work.

This is delphi compatible.

Michael.