From: chris <spamoff.danx@ntlworld.com>
Subject: Deallocation & Tagged Types
Date: Sat, 18 Oct 2003 21:53:02 +0100
Date: 2003-10-18T21:53:02+01:00 [thread overview]
Message-ID: <5Fhkb.3195$KA5.27417@newsfep4-glfd.server.ntli.net> (raw)
Hi,
I've got a situation involving deallocating an object from a proxy and
am a bit stuck... Namely how to deallocate an object belonging to a
particular class but not knowing the specific type.
The example is not from the code, it just highlights the problem...
-- a vehicles package
--
package Vehicles is
type Vehicle is abstract tagged null record;
type Vehicle_Access is access all Vehicle'class;
procedure Destroy (V : in out Vehicle) is abstract;
end Vehicles;
-- proxies for vehicles
--
package Vehicle_Proxy is
type Proxy is new Vehicle with private;
procedure Destroy (V : in out Proxy);
private
type Proxy is new Vehicle with record
Actual : Vehicle_Access;
end record;
end Vehicle_Proxy;
package body Vehicle_Proxy is
procedure Destroy (V : in out Proxy) is
begin
Destroy (V.Actual.all);
-- now what???
end Destroy;
end Vehicle_Proxy;
If V.Actual isn't properly disposed of, the proxy will leak. What's the
best way to handle this? One way I can think of is to do something like
this...
type Vehicle_Deallocator
is access procedure (V : in out Vehicle_Access);
and revise type Proxy to the following,
type Proxy is new Vehicle with record
Actual : Vehicle_Access;
Dealloc : Vehicle_Deallocator;
end record;
and Destroy to
procedure Destroy (V : in out Proxy) is
begin
Destroy (V.Actual.all);
V.Dealloc (V.Actual);
V.Actual := null;
end Destroy;
Is there another way that I'm missing or is this how people do this in
their code? I also came up against this when making a container type (a
container for rasters in the real code). Namely if you stuff
Raster_Access into a container (an Image) and destroy the Image
container, you need to deallocate the rasters. That means you need to
have a deallocator capable of handling the types derived from Raster.
If you miss one, the code breaks.
The alternative is to deallocate each raster outside of the image
container, but you still need someway of handling each subclass of raster.
Cheers,
Chris
next reply other threads:[~2003-10-18 20:53 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-10-18 20:53 chris [this message]
2003-10-19 15:38 ` Deallocation & Tagged Types Robert I. Eachus
2003-10-19 16:53 ` chris
2003-10-20 1:08 ` Robert I. Eachus
2003-10-19 16:10 ` Dmitry A. Kazakov
2003-10-19 16:50 ` chris
2003-10-20 1:13 ` Robert I. Eachus
2003-10-20 1:43 ` Hyman Rosen
2003-10-26 8:11 ` Patrice Freydiere
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