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From: mheaney@on2.com (Matthew Heaney)
Newsgroups: comp.lang.ada
Subject: Re: A tiny little integer stack package from a novice.
Date: 25 Nov 2002 09:31:57 -0800
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Stapler <spam.magnet@yahoo.com> wrote in message news:<S9kE9.106573$__1.63580@rwcrnsc51.ops.asp.att.net>...
> generic
> 
> 	Size : Positive;
> 		
> package int_stack is
> 	
> 	type Int_Stack is limited private;
> 	type Stack_Ptr is limited private;
> 	
> 	procedure Push(X : in Integer);
> 	procedure Free_Stack;
> 	
> 	function Pop return Integer;
> 	
> private
> 
> 	
> 	type Int_Stack is array(1..Size) of Integer;
> 	type Stack_Ptr is access all Int_Stack;
> 	The_Stack : Stack_Ptr := new Int_Stack;	-- Provides access for De-allocation of entire stack
> 						-- Is also the sole allocation point for this package.
> 	procedure Free is new Ada.Unchecked_Deallocation(Int_Stack, Stack_Ptr);
> 	
> end int_stack;


Why is this a generic package?  Why isn't this an abstract data type?

If the stack has a fixed, maximum size, it's easier to simply declare
it as a discriminated record, which avoids all the headaches
associated with memory allocation.  For example:

package Integer_Stacks is

   pragma Pure (Integer_Stacks);

   type Stack_Type (Size : Natural) is limited private;
...
private

   type Integer_Array is array (Positive range <>) of Integer;

   type Stack_Type (Size : Natural) is
      limited record
         Elements : Integer_Array (1 .. Size);
         Top      : Natural := 0;
      end record;

end Integer_Stacks;