Arthur, that code is for FPC. But this might be IDE independent:
Code:
{$IFDEF FPC}
operator +(v1, v2: TVector2d) result: TVector2d;
{$ELSE}
class operator TVector2d.add(v1, v2: TVector2d): TVector2d;
{$IFEND} 
begin
  Result.x := v1.x  + v2.x;
  Result.y := v1.y + v2.y;
end;
In the same case you can just rename it to TPoint instead if you want to.