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From: Roland Illig <roland.illig@gmx.de>
Newsgroups: comp.lang.ada
Subject: Re: [newbie] simple(?) data structures
Date: Sun, 13 Jun 2004 05:13:11 +0200
Message-ID: <2j1v28Fs989jU1@uni-berlin.de>
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Date: 2004-06-13T05:13:11+02:00
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Ludovic Brenta wrote:
> 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;

That looks cool to me. That's exactly as I wanted it. (Burden the 
compiler with all those range checking :))

> 
> 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

Many thanks for your detailed answer. Now I know what I forgot to say. 
The thing that makes the definition of the data structure that 
complicated is that I want to choose the size of the Go_Board at runtime 
and I want to pass that Go_Board to other subprograms. Is that possible 
with packages?

--   function New_Board(The_Size : Integer) return Go_Board is
--      package The_Board is new Go_Board (Size => The_Size);
--   begin
--      return The_Board;
--   end New_Board;

--   procedure Print_Board(Board : Go_Board) is
--   begin
--     null;
--   end Print_Board;

> (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)

I like that style. It's almost equal to my own.

> HTH
It did a lot. Thanks again.

Roland