Re: Pure, Storage_Size and Unchecked_Conversion

[Martin Krischik <krischik@users.sourceforge.net>]

Y.Tomino wrote:

> Hi.
> I compiled the package like this with gcc 4.2.
> 
> with Ada.Unchecked_Conversion;
> package Pure_SS_Unc is
>    pragma Pure;
>    type T is access Integer;
>    for T'Storage_Size use 0;
>    function F1 (X : Integer) return T;
>    function F2 is new Ada.Unchecked_Conversion (Integer, T);
> end Pure_SS_Unc;

You are aware that this will only work on 32 bit system while 64 bit is the
future. It does - of course - not mean that you can't do it. You just have
to do it right.

Read:

http://en.wikibooks.org/wiki/Ada_Programming/Types/access#Where_is_void.2A.3F

In short: don't use the predefined integer - use your own:

type void is mod System.Memory_Size;
for void'Size use System.Word_Size;

> pure_ss_unc.ads:7:58: named access types not allowed in pure unit

It's one of the definitions of a pure unit: no named access types. It you
read the Distributed System Annex then you will see why it has to be that
way.

Martin
-- 
mailto://krischik@users.sourceforge.net
Ada programming at: http://ada.krischik.com