From: "Randy Brukardt" <randy@rrsoftware.com>
Subject: Re: volatile vs aliased
Date: Wed, 5 Oct 2005 18:38:52 -0500
Date: 2005-10-05T18:38:52-05:00 [thread overview]
Message-ID: <p_GdnTN0co2x_tneRVn-uA@megapath.net> (raw)
In-Reply-To: 87mzlnomca.fsf@ludovic-brenta.org
"Ludovic Brenta" <ludovic@ludovic-brenta.org> wrote in message
news:87mzlnomca.fsf@ludovic-brenta.org...
...
> In your situation, it seems that you want something like this
> (which, incidentally, I use very often):
>
> type T is ...;
>
> procedure Read_Variable (At_Address : in System.Address;
> Into : out T) is
> V : aliased T;
> -- suppress default initialisation, I know what I'm doing.
> pragma Import (Ada, V);
> for V'Address use At_Address;
> begin
> -- perform my own explicit validation of the variable, perhaps
> -- using 'Valid; then, copy into Into:
> Into := V;
> end Read_Variable;
This seems like a good time to mention that I think the explicit use of
System.Address in Ada 95 and Ada 200Y code is usually a mistake. Since
pragma Convention can be used to ensure that general access types have the
appropriate representation, its rare that Address needs to be used for
interfacing. (There is only a handful of uses of Address in Claw, for
example.)
Moreover, when you *do* need to use it, Address_to_Access_Conversions is the
best way to convert it, not an overlay (which at best blocks optimizations
and at worst won't even work right).
type T is ...;
procedure Read_Variable (At_Address : in System.Address;
Into : out T) is
package AAC is new System.Address_to_Access_Conversions (T);
V : AAC.Object_Pointer := AAC.To_Pointer (At_Address);
begin
-- perform my own explicit validation of the pointer's contents, perhaps
-- using 'Valid; then, copy into Into:
Into := V.all;
end Read_Variable;
But it is better still to declare an appropriate type and never use Address
in the first place:
type Pointer_T is access all T;
pragma Convention (C, Pointer_T);
Address clauses should be restricted to mapping to hardware, IMHO.
Randy.
next prev parent reply other threads:[~2005-10-05 23:38 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-10-05 15:22 volatile vs aliased REH
2005-10-05 18:22 ` Ludovic Brenta
2005-10-05 18:39 ` REH
2005-10-05 19:46 ` Ludovic Brenta
2005-10-05 20:02 ` REH
2005-10-05 20:11 ` Ludovic Brenta
2005-10-05 20:20 ` REH
2005-10-06 5:21 ` Ludovic Brenta
2005-10-05 20:55 ` Simon Wright
2005-10-06 18:32 ` Jeffrey R. Carter
2005-10-05 23:38 ` Randy Brukardt [this message]
2005-10-06 0:02 ` tmoran
2005-10-06 13:40 ` REH
2005-10-06 23:52 ` Randy Brukardt
2005-10-06 18:40 ` Jeffrey R. Carter
2005-10-06 19:37 ` Robert A Duff
2005-10-06 23:56 ` Randy Brukardt
2005-10-06 19:08 ` REH
2005-10-06 19:21 ` Ed Falis
2005-10-06 19:37 ` REH
2005-10-06 19:46 ` Robert A Duff
2005-10-06 8:05 ` Martin Krischik
2005-10-06 8:52 ` Dmitry A. Kazakov
2005-10-06 11:36 ` Rolf
2005-10-06 18:43 ` Björn Persson
2005-10-06 19:03 ` Niklas Holsti
2005-10-07 6:36 ` Martin Krischik
2005-10-07 6:33 ` Martin Krischik
2005-10-07 15:56 ` Adrian Knoth
2005-10-07 18:48 ` Martin Krischik
2005-10-07 22:44 ` REH
2005-10-08 6:10 ` Simon Wright
2005-10-17 2:16 ` Dave Thompson
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