From: "Dan'l Miller" <optikos@verizon.net>
Subject: Re: Visibility of Indexing aspects
Date: Tue, 7 Aug 2018 08:13:03 -0700 (PDT)
Date: 2018-08-07T08:13:03-07:00 [thread overview]
Message-ID: <62cefa64-4855-4d51-9216-519f260349d4@googlegroups.com> (raw)
In-Reply-To: <pkafj7$5tg$1@franka.jacob-sparre.dk>
On Monday, August 6, 2018 at 4:46:16 PM UTC-5, Randy Brukardt wrote:
> "Dan'l Miller" wrote in message
> news:cc25c794-5986-4f6e-9d5e-0ec20a4f47d0@googlegroups.com...
> ...
> >Ummmmmmmmm, what is so incredibly "expensive" about Element =>
> >Self.Data(Index)'Access in OP?
>
> Nothing is expensive about *that*, but it's also very unsafe by itself (this
> either prevents a container from ever reusuing memory, or essentially
> requires being OK with dangling pointers and the erroneousness that they
> cause).
>
> Our requirement was that the user-defined dereference mechanism needs to be
> safe (at least possible to be safe), and that requires the container to be
> able to find out when the dereference ceases to exist. At that point, the
> container can free the underlying memory if need be. (For an extreme
> example, consider a persistent container, where the object only should exist
> in memory so long as it is being used there.) The design that we came up
> with for Ada 2012 uses finalization for this notification; we looked at
> other mechanisms, but they would have had similar overhead.
>
> The Ada containers use the finalization to clear the tampering check (which
> prevents deleting of elements while the dereference exists); other uses are
> possible, of course.
>
> Without these sorts of checks, Ada containers would be no more safe than C
> code. In particular, Ada programmers do not expect checked indexing to be
> unsafe, so syntax of C(I) being unsafe would be a particular surprise.
>
> Randy.
My reference-counting of aliases in my reply above concurs with what you saying in this reply of yours.
Randy, you make a strong argument for the compiler/language tracking the lifetime of aliases instead of leaving it as a library and/or app-domain responsibility.
next prev parent reply other threads:[~2018-08-07 15:13 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-02 20:31 Visibility of Indexing aspects Randy Brukardt
2018-08-03 0:43 ` Dan'l Miller
2018-08-03 20:56 ` Randy Brukardt
2018-08-03 21:32 ` Dan'l Miller
2018-08-06 21:46 ` Randy Brukardt
2018-08-06 22:12 ` Dmitry A. Kazakov
2018-08-07 15:13 ` Dan'l Miller [this message]
2018-08-07 22:41 ` Randy Brukardt
-- strict thread matches above, loose matches on Subject: below --
2018-07-14 14:18 Jere
2018-07-14 17:04 ` Shark8
2018-07-14 18:29 ` Jere
2018-07-14 18:41 ` Dmitry A. Kazakov
2018-07-14 23:00 ` Shark8
2018-07-14 23:28 ` Jere
2018-07-15 14:41 ` AdaMagica
2018-07-15 15:33 ` Jere
2018-07-16 3:22 ` AdaMagica
2018-07-17 0:35 ` Jere
2018-07-17 9:46 ` AdaMagica
2018-07-17 10:11 ` AdaMagica
2018-07-20 12:08 ` Jere
2018-07-20 16:11 ` AdaMagica
2018-07-20 22:03 ` Dan'l Miller
2018-07-20 22:07 ` Jere
2018-07-21 10:33 ` AdaMagica
2018-07-24 3:32 ` Randy Brukardt
2018-07-24 17:15 ` Dan'l Miller
2018-07-25 5:37 ` Randy Brukardt
2018-07-25 18:26 ` Dan'l Miller
2018-07-25 19:58 ` AdaMagica
2018-07-25 20:57 ` Dan'l Miller
2018-07-26 0:12 ` Randy Brukardt
2018-07-26 2:41 ` Dan'l Miller
2018-07-26 19:09 ` Randy Brukardt
2018-07-26 20:31 ` Shark8
2018-07-26 21:25 ` Dan'l Miller
2018-07-27 22:05 ` Randy Brukardt
2018-07-28 0:35 ` Dan'l Miller
2018-07-27 21:58 ` Randy Brukardt
2018-07-20 22:23 ` Jere
2018-07-20 22:25 ` Jere
2018-07-21 5:58 ` J-P. Rosen
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