Re: Newbie question

[Ludovic Brenta <ludovic@ludovic-brenta.org>]

On Mar 12, 3:32 pm, stefan-lu...@see-the.signature wrote:
> On Thu, 12 Mar 2009, Olivier Scalbert wrote:
> > Ludovic Brenta wrote:
>
> > > Solution 2: merge the Boolean directly into Piece_T:
>
> > > type Piece_T (Present : Boolean) is record
> > >    case Present is
> > >       when True =>
> > >          Color : Color_T;
> > >          Piece_Type : Piece_Type_T;
> > >       when False =>
> > >          null;
> > >    end case;
> > > end record;
>
> Solution 2a: Use an enumeration:
>
> type Color_T is (Black, White, None);
>
> type Piece_T(Color: Color_T) is
>   record
>     case Color is
>       when White =>
>         White_Piece: Piece_Type_T;
>       when Black =>
>         Black_Piece: Piece_Type_T;
>       when None =>
>         null;
>     end case;
>   end record;

The problem with this is that you'd then need two code paths for
Black_Piece and White_Piece, every time. To overcome this, here is
solution 2a1:

type Square_T (Color : Color_T := None) is record
   case Color is
      when None => null;
      when Black | White => Piece_Type : Piece_Type_T;
   end case;
end record;

--
Ludovic Brenta.