Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.c++ > #120835

Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe"

Path csiph.com!weretis.net!feeder9.news.weretis.net!news.quux.org!eternal-september.org!feeder2.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail
From Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups comp.lang.c++
Subject Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe"
Date Mon, 04 Nov 2024 06:59:14 -0800
Organization A noiseless patient Spider
Lines 84
Message-ID <86cyjbt58d.fsf@linuxsc.com> (permalink)
References <ve4mun$2cn9s$2@dont-email.me> <vfmh6v$ksdf$1@dont-email.me>
MIME-Version 1.0
Content-Type text/plain; charset=us-ascii
Injection-Date Mon, 04 Nov 2024 15:59:18 +0100 (CET)
Injection-Info dont-email.me; posting-host="f359696380662fa6462481cb0fc8fe02"; logging-data="1056401"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1+emhrDImXbBip2Uxh5ITToQCMfXhHH9dY="
User-Agent Gnus/5.11 (Gnus v5.11) Emacs/22.4 (gnu/linux)
Cancel-Lock sha1:3xjWv0gpmXsFsGqKH0oGH4CpSNo= sha1:mIZXLcTmcON0ST3FzaCAAmhOVNs=
Xref csiph.com comp.lang.c++:120835

Show key headers only | View raw

jseigh <jseigh_es00@xemaps.com> writes:

[...]

> You create a new nullable attribute for pointers.  That
> would make the pointer behave like void* instead of T*.
> You could move, copy, and compare, but you could not
> dereference them.  If you wanted to dereference them
> you would have to apply a special not_null unary predicate
> to them.  What makes it special is the boolean result
> is only valid inside a conditional expression.  It's
> not copyable or referencable.  You could have 1 or
> more of these in a conditional expression along with
> ordinary predicates with the restriction that the
> expression has to be formed such that if any of the
> not_null terms are false, the expression has to
> evaluate as false.
>
> The other thing that makes not_null is that inside
> if the conditional statements true blocks, the
> nullable pointer gets it T* properties back, so
> you can dereference it, but again only in the
> true blocks.  So for example
>
> nullable T* p = &something;
>
> T p2 = *p;	// invalid, compiler thinks you are trying
>                 // do dereference void*
>
> not_null(p);	// invalid, not inside conditional expression
>
> if (not_null(p)
>   p2 = *p;      // valid
> else
>   p2 = *p;      // invalid
>
>
> Traversing a linked list would look like
>
> T* p = head;
> while (not_null(p)) {
>   ...
>   p = p->next;	// valid, inside while true block
> }
>
> not_null would look like
> __predicate_bool not_null(T *&)
> It would make a const copy of T*, test that,
> cast to T*, use it for the true block.
>
> So no NPEs possible for pointer with this
> attribute.

A few comments.

An "attribute" should be placed like a qualifier, next
to the pointer, rather than before the type specifier.

The sense of the attribute should be "never null" rather
than "nullable".  Ordinary pointers are nullable;  what
is needed is a way to indicate that a particular pointer
(either a variable or the return value of a function) will
never be null.

I expect there are implications for pointers to never-null
pointers, but I haven't tried to work out what they need
to be.  Example:  'T *nevernull *p;'.  What are the rules
for assigning to p?

Ordinary pointers can (sometimes) be determined to be
non-null using data flow analysis (like what you say in
the followup post for the linked list example).

There is no need for not_null().  If we see

    if(p){ ... }

or

    while(p){ ... }

we know that p will not be null inside the controlled
statement (subject to change if there is an assignment
to p, per the data flow remark above).

Back to comp.lang.c++ | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

"Safe C++ is A new Proposal to Make C++ Memory-Safe" Lynn McGuire <lynnmcguire5@gmail.com> - 2024-10-08 20:40 -0500
  Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" Michael S <already5chosen@yahoo.com> - 2024-10-09 14:14 +0300
  Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" Lynn McGuire <lynnmcguire5@gmail.com> - 2024-10-09 15:02 -0500
    Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" Michael S <already5chosen@yahoo.com> - 2024-10-09 23:46 +0300
      Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" Muttley@DastartdlyHQ.org - 2024-10-10 08:34 +0000
        Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" Michael S <already5chosen@yahoo.com> - 2024-10-10 12:51 +0300
          Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" Muttley@DastartdlyHQ.org - 2024-10-10 10:20 +0000
            Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" Michael S <already5chosen@yahoo.com> - 2024-10-10 13:44 +0300
              Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" Muttley@DastartdlyHQ.org - 2024-10-10 10:50 +0000
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" Michael S <already5chosen@yahoo.com> - 2024-10-10 14:10 +0300
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" Muttley@DastartdlyHQ.org - 2024-10-10 13:11 +0000
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" Michael S <already5chosen@yahoo.com> - 2024-10-10 16:54 +0300
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" Paavo Helde <eesnimi@osa.pri.ee> - 2024-10-10 18:08 +0300
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" wij <wyniijj5@gmail.com> - 2024-10-10 23:37 +0800
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" Paavo Helde <eesnimi@osa.pri.ee> - 2024-10-10 19:03 +0300
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" Michael S <already5chosen@yahoo.com> - 2024-10-10 19:11 +0300
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" David Brown <david.brown@hesbynett.no> - 2024-10-10 20:01 +0200
          Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-10-10 07:56 -0700
            Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" Michael S <already5chosen@yahoo.com> - 2024-10-10 18:56 +0300
    Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" Ross Finlayson <ross.a.finlayson@gmail.com> - 2024-10-20 10:13 -0700
  Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" jseigh <jseigh_es00@xemaps.com> - 2024-10-10 12:13 -0400
  Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" Bonita Montero <Bonita.Montero@gmail.com> - 2024-10-10 18:29 +0200
  Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" Vir Campestris <vir.campestris@invalid.invalid> - 2024-10-20 12:37 +0100
    Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" Michael S <already5chosen@yahoo.com> - 2024-10-20 14:46 +0300
      Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" Muttley@DastartdlyHQ.org - 2024-10-20 14:23 +0000
  Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" jseigh <jseigh_es00@xemaps.com> - 2024-10-27 19:09 -0400
    Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" jseigh <jseigh_es00@xemaps.com> - 2024-10-27 20:40 -0400
      Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" wij <wyniijj5@gmail.com> - 2024-10-28 09:22 +0800
        Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-10-27 21:18 -0700
          Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" jseigh <jseigh_es00@xemaps.com> - 2024-10-28 12:25 -0400
            Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" jseigh <jseigh_es00@xemaps.com> - 2024-10-30 12:56 -0400
              Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-10-30 12:50 -0700
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" jseigh <jseigh_es00@xemaps.com> - 2024-10-30 16:31 -0400
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-11-04 12:47 -0800
              Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" jseigh <jseigh_es00@xemaps.com> - 2024-11-07 07:02 -0500
              Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" Lynn McGuire <lynnmcguire5@gmail.com> - 2024-11-07 20:14 -0600
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" jseigh <jseigh_es00@xemaps.com> - 2024-11-08 09:40 -0500
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" scott@slp53.sl.home (Scott Lurndal) - 2024-11-08 14:48 +0000
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" Muttley@DastartdlyHQ.org - 2024-11-08 14:54 +0000
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-11-08 12:40 -0800
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" Muttley@dastardlyhq.com - 2024-11-09 12:01 +0000
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-11-09 12:39 -0800
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" Muttley@DastartdlyHQ.org - 2024-11-11 09:56 +0000
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-11-11 13:36 -0800
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" Muttley@DastartdlyHQ.org - 2024-11-12 08:28 +0000
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-11-12 13:56 -0800
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-11-12 13:59 -0800
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" Ross Finlayson <ross.a.finlayson@gmail.com> - 2024-11-12 16:20 -0800
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" Ross Finlayson <ross.a.finlayson@gmail.com> - 2024-11-10 13:02 -0800
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" Ross Finlayson <ross.a.finlayson@gmail.com> - 2024-11-10 13:05 -0800
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-11-08 12:46 -0800
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" wij <wyniijj5@gmail.com> - 2024-11-09 05:18 +0800
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-11-08 13:23 -0800
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" wij <wyniijj5@gmail.com> - 2024-11-09 05:25 +0800
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-11-08 13:27 -0800
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" wij <wyniijj5@gmail.com> - 2024-11-09 06:02 +0800
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-11-08 14:09 -0800
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" wij <wyniijj5@gmail.com> - 2024-11-09 06:35 +0800
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-11-08 14:37 -0800
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" wij <wyniijj5@gmail.com> - 2024-11-09 06:47 +0800
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-11-08 14:58 -0800
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" wij <wyniijj5@gmail.com> - 2024-11-09 07:09 +0800
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-11-08 15:35 -0800
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" scott@slp53.sl.home (Scott Lurndal) - 2024-11-08 23:50 +0000
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-11-08 18:11 -0800
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-11-08 14:39 -0800
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" wij <wyniijj5@gmail.com> - 2024-11-09 06:58 +0800
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-11-08 15:01 -0800
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" wij <wyniijj5@gmail.com> - 2024-11-09 07:13 +0800
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-11-08 15:40 -0800
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" wij <wyniijj5@gmail.com> - 2024-11-09 08:19 +0800
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-11-08 18:15 -0800
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" scott@slp53.sl.home (Scott Lurndal) - 2024-11-09 16:23 +0000
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-11-09 12:42 -0800
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" scott@slp53.sl.home (Scott Lurndal) - 2024-11-09 23:23 +0000
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" Paavo Helde <eesnimi@osa.pri.ee> - 2024-11-10 11:00 +0200
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-11-12 16:56 -0800
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-11-12 16:59 -0800
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-11-12 17:05 -0800
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" Muttley@dastardlyhq.com - 2024-11-09 12:01 +0000
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" Muttley@dastardlyhq.com - 2024-11-09 12:01 +0000
                Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-11-09 12:50 -0800
    Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" Tim Rentsch <tr.17687@z991.linuxsc.com> - 2024-11-04 06:59 -0800
  Re: "Safe C++ is A new Proposal to Make C++ Memory-Safe" jseigh <jseigh_es00@xemaps.com> - 2024-11-30 10:03 -0500

csiph-web