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Groups > comp.lang.c++ > #120835
| 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 | 2024-11-04 06:59 -0800 |
| Organization | A noiseless patient Spider |
| Message-ID | <86cyjbt58d.fsf@linuxsc.com> (permalink) |
| References | <ve4mun$2cn9s$2@dont-email.me> <vfmh6v$ksdf$1@dont-email.me> |
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).
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"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
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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
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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
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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
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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
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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
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