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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Large arrays (again), problem case for GNAT
Newsgroups: comp.lang.ada
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Date: Fri, 15 Apr 2005 15:21:32 +0200
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Date: 2005-04-15T15:21:32+02:00
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On Fri, 15 Apr 2005 11:49:23 GMT, Dr. Adrian Wrigley wrote:

> On Fri, 15 Apr 2005 00:21:50 -0500, Randy Brukardt wrote:
> 
>> My pool expands
>> the arrays by rewriting the dope of the arrays passed into the functions -
>> something that no one should ever do unless they're the author of the
>> compiler. And probably not even then.
> 
> I did this a lot a few years ago with GNAT.  It worked extremely well.
> (no I'm not the author of the compiler!)
> 
> I couldn't understand why there was no decent mechanism for changing
> the size of an array.  The resulting code was much cleaner, faster
> and more memory efficient than using fancy data structures/container
> libraries.
> 
> Why did the language not provide an equivalent of 'realloc' for
> arrays?

I would propose:

generic
   type Element_Type is limited private;
   type Index_Type is (<>);
   type Array_Type is array (Index_Type) of Element_Type;
   type Access_Type is access Array_Type;
procedure Ada.Array_Resize (X : in out Access_Type; Elements : Integer);

and 

generic
   type Element_Type is private;
   type Index_Type is (<>);
   type Array_Type is array (Index_Type) of Element_Type;
   type Access_Type is access Array_Type;
procedure Ada.Array_Expand
   (  X : in out Access_Type;
      Elements : Natural;
      Initial : Element_Type
   );

- Element_Type is limited in the variant with 2 arguments and for an actual
array of limited elements the implementation ensures that the result will
not be moved in the address space. Otherwise Storage_Error is propagated.

- For arrays of non-limited components the implementation is free to copy,
adjust, finalize elements.

- When Elements is negative the removed elements are properly finalized.

- Storage_Error is propagated when the array wasn't re-sized as required,
but X.all is valid.

- Program_Error is propagated when X.all becomes invalid, for example after
element's initialization/finalization exceptions.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de