program Project15; {$APPTYPE CONSOLE} {$R *.res}

uses System.SysUtils;

type
   IMyInterface = interface
      procedure interfaceProc();
   end;

   TMyBase = class(TInterfacedObject, IMyInterface)
      procedure interfaceProc();// virtual;
   end;

   TMyChild = class(TMyBase, IMyInterface)
      procedure interfaceProc();// override;
   end;

procedure TMyBase.interfaceProc();
begin
   WriteLn('TMyBase');
end;

procedure TMyChild.interfaceProc();
begin
   inherited;
   Writeln('TMyChild');
end;

var
   interfaceVariable: IMyInterface;
   classVariable: TMyBase;
begin
   WriteLn('interface variable');
   interfaceVariable := TMyChild.Create();
   interfaceVariable.interfaceProc();

   Write(sLineBreak);

   WriteLn('class type variable');
   classVariable := TMyChild.Create();
   classVariable.interfaceProc();

   readln;
end.

interface variable
TMyBase
TMyChild

class type variable
TMyBase