[fpc-devel] interfaces / inheritance / again

[Martin Frb]

On 02/02/2026 22:59, Michael Van Canneyt via fpc-devel wrote:
>
>
> On Mon, 2 Feb 2026, Martin Frb via fpc-devel wrote:
>
>>
>>
>> In a class, an overridden function can actually return a subclass of 
>> what the virtual method returned.
>
> I don't understand this remark. Please explain ?

See below, the overriden method returns a subclass. (works with subclass 
as result too).

program Project1;
{$Mode objfpc}{$Interfaces corba}
type
   IFoo = interface end;
   IFoo2 = interface(IFoo) end;

   TBar = class
     function abc: IFoo; virtual;
   end;

   TBar2 = class(TBar)
     function abc: IFoo2; override; // inherited interface as result type
   end;

function TBar2.abc: IFoo2;
begin
end;
function TBar.abc: IFoo;
begin
end;

begin
end.