When a class implements a descendant interface, why doesn't it automatically count as implementing the base interface?

Question

What\'s the reason this won\'t compile?

type
  IInterfaceA = interface [\'{44F93616-0161-4912-9D63-3E8AA140CA0D}\']
    procedure DoA;
  end;

  IInterfaceB          


        

Answer 1

Another way to make it work is to include both interfaces in the class declaration.

TImplementsAB = class(TSingletonImplementation, IInterfaceA, IInterfaceB)
  procedure DoA;
  procedure DoB;
end;

I guess this is what is required for the compiler to realize that TImplementsAB implements both IInterfaceA and IInterfaceB.