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Newsgroups: comp.lang.ada
Subject: Re: [newbie] simple(?) data structures
References: <2j1e30Fsrg8vU1@uni-berlin.de>
From: Ludovic Brenta <ludovic.brenta@insalien.org>
Date: Sun, 13 Jun 2004 02:10:50 +0200
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Date: 2004-06-13T02:10:09+02:00
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Roland Illig writes:
> I'm doing my first steps with Ada. I tried to model a Go board and
> failed. In Java/C++, I would do it like this:

[...]

> How can I do this in Ada? I already tried something with packages
> and generics, but that did not look nice. But I want it to look nice
> and Adaish.

Cool, great attitude.  Here is how I would do it, using generics like
you suggested:

generic
   Size : in Positive;
package Go_Board is
   type Width is range 1 .. Size;
   type Height is range 1 .. Size;

   type Stone is (Empty, Black, White);

   function Get_Stone (X : in Width; Y : in Height) return Stone;
   procedure Set_Stone (X : in Width; Y : in Height; S : in Stone);
private
   Board : array (Width, Height) of Stone;
end Go_Board;


Each instance of this package contains one board; thus you do not need
a constructor.  To create an instance:

with Ada.Text_IO;
with Go_Board;
procedure Test_Go_Board is
   package The_Board is new Go_Board (Size => 10);
begin
   for X in The_Board.Width loop
      for Y in The_Board.Height loop
         The_Board.Set_Stone (X, Y, The_Board.Empty);
         Ada.Text_IO.Put_Line ("Board (" & Integer'Image (X) & ", " &
                               Integer'Image (Y) & ") := " &
                               The_Board.Stone'Image
                                  (The_Board.Get_Stone (X, Y)));
       end loop;
   end loop;

   Ada.Text_IO.Put_Line ("Width of the board is " &
                         Integer'Image (The_Board.Width'Last - 
                                        The_Board.Width'First));

   Ada.Text_IO.Put_Line ("Height of the board is " &
                         Integer'Image (The_Board.Height'Last - 
                                        The_Board.Height'First));
end Test_Go_Board;


You may also want helper functions in the package Go_Board:

   function Height return Positive is
   begin
      return Size;
   end Height;

(note that I avoided using "use Ada.Text_IO; use The_Board" because I
wanted to make things really obvious; but you may want to consider
using such use clauses if you think the code is too cluttered)

HTH

-- 
Ludovic Brenta;