From: Simon Wright <simon@pushface.org>
Subject: Re: On absurdity of collections 7.6.1 (11.1/3)
Date: Wed, 29 Sep 2021 22:38:42 +0100 [thread overview]
Message-ID: <ly35pnawpp.fsf@pushface.org> (raw)
In-Reply-To: sj1i6g$7hv$1@gioia.aioe.org
"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:
> On 2021-09-29 13:05, Simon Wright wrote:
>> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:
>>
>>> type Item_Ptr is access all Item;
>>> function New_Item
>>> ( Pool : in out Root_Storage_Pool'Class;
>>> Text : String
>>> ) return Item_Ptr;
>> What I don't see is how you can implement this, never mind any other
>> problems.
>
> A naive, but wrong due to 7.6.1 (11.1/3) nonsense, implementation would be:
>
> function New_Item
> ( Pool : in out Root_Storage_Pool'Class;
> Text : String
> ) return Item_Ptr is
> type Ptr is access Item;
> for Ptr'Storage_Pool use Pool;
> Object : Ptr := new Item (Text'Length);
> begin
> Object.Text := Text;
> return Object.all'Unchecked_Access;
> end New_Item;
OK, that code compiles.
What you'd need to happen when the returned Item_Ptr is freed would be
for the mechanism of the actual pool to be invoked. But Item_Ptr was
declared without any pool specified, so uses the default, and when the
returned Item_Ptr is freed it uses the default pool's mechanism.
But of course what actually happens with this code is that the returned
Item_Ptr is left dangling; my test
with P;
with System.Pool_Local; -- GNAT special
with Ada.Text_IO; use Ada.Text_IO;
procedure Test is
use P;
Pool : System.Pool_Local.Unbounded_Reclaim_Pool;
Ptr : Item_Ptr := New_Item (Pool, "hello");
begin
Put_Line (Ptr.Text);
Free (Ptr);
end Test;
manages flukily to print "hello" before crashing at the Free (Ptr).
I don't see how what you want can be achieved without every access type
containing a reference to the pool the object was allocated from.
next prev parent reply other threads:[~2021-09-29 21:38 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-29 9:09 On absurdity of collections 7.6.1 (11.1/3) Dmitry A. Kazakov
2021-09-29 11:05 ` Simon Wright
2021-09-29 11:20 ` Dmitry A. Kazakov
2021-09-29 21:38 ` Simon Wright [this message]
2021-09-30 8:07 ` Dmitry A. Kazakov
2021-09-30 8:35 ` Simon Wright
2021-09-30 8:49 ` Dmitry A. Kazakov
2021-10-01 1:37 ` Randy Brukardt
2021-10-01 7:57 ` Dmitry A. Kazakov
2021-09-30 0:23 ` Randy Brukardt
2021-09-30 8:06 ` Dmitry A. Kazakov
2021-09-30 18:23 ` G.B.
2021-09-30 18:52 ` Dmitry A. Kazakov
2021-10-01 1:40 ` Randy Brukardt
2021-10-01 7:57 ` Dmitry A. Kazakov
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