Hi Andrew,

See my proposal "Towards a Better Allocator Model" and new thread in
this news group.
http://home.earthlink.net/~phalpern/cpp/HalpernAllocatorProposal.pdf .

To summarize: I use basic principles to argue for a modified option 2
(slow copy), but also recommend that both types of swap be available.
The paper talks about much more than Issue 431.  The solution proposed
to Issue 431 is simply an outgrowth of the the principles described in
the paper.

apm35@student.open.ac.uk wrote:

>Hello,
>
>Does anyone know what progress has been made on issue 431 (unequal
>allocators)? I  see from
>http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2004/n1599.html that
>several possibilities have been presented. I am interested in knowing
>which way, if any, the stds committee are leaning.
>Regards,
>
>Andrew Marlow
>
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Pablo Halpern                 phalpern@halpernwightsoftware.com
Author: The C++ Standard Library from Scratch
http://www.halpernwightsoftware.com/stdlib-scratch

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Howard Hinnant wrote:
> In article <1103894340.612771.137220@z14g2000cwz.googlegroups.com>,
> To the best of my knowledge, the subject has not been discussed in
> committee since N1599 was written.  I anticipate that it will be a
very
> contentious issue among vendors, as each of the three options is
> strongly supported by at least one vendor.

Does that mean it will be *impossible* to get this resolved?
Surely picking one of the options is better than what we have at the
moment!

>
> I would like to summarize option 3 with a succinct lemma:
>
> Allocators own resources.  In the context of unequal allocators,
> allocator state should stay with the resources it owns.  If resource
> ownership is to be transferred elsewhere, allocator state should
follow
> the resource.

Sounds reasonable to me :-)

> http://home.twcny.rr.com/hinnant/cpp_extensions/unique_ptr.html
>
> With such a smart pointer, allocators can become deleters with an
> appropriate adaptor.  Therefore there is more than just an analogy
> between allocators and deleters.  There is an opportunity for a
> consistent overall design with interchangeable and reusable code.
Is this an officially proposed extension?

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In article <1104860533.502277.246990@c13g2000cwb.googlegroups.com>,
 apm35@student.open.ac.uk wrote:

> Howard Hinnant wrote:
> > In article <1103894340.612771.137220@z14g2000cwz.googlegroups.com>,
> > To the best of my knowledge, the subject has not been discussed in
> > committee since N1599 was written.  I anticipate that it will be a
> very
> > contentious issue among vendors, as each of the three options is
> > strongly supported by at least one vendor.
>
> Does that mean it will be *impossible* to get this resolved?
> Surely picking one of the options is better than what we have at the
> moment!

I surely hope that it is not impossible to resolve this issue.  If
enough non-vendors weigh in, and happen to show a preponderance of
support for one of the options, then I'm sure vendors will come around.
Vendors exist to serve their customers, else they will end up with none.

> > I would like to summarize option 3 with a succinct lemma:
> >
> > Allocators own resources.  In the context of unequal allocators,
> > allocator state should stay with the resources it owns.  If resource
> > ownership is to be transferred elsewhere, allocator state should
> follow
> > the resource.
>
> Sounds reasonable to me :-)

Great, help me spread the word. ;-)

> > http://home.twcny.rr.com/hinnant/cpp_extensions/unique_ptr.html
> >
> > With such a smart pointer, allocators can become deleters with an
> > appropriate adaptor.  Therefore there is more than just an analogy
> > between allocators and deleters.  There is an opportunity for a
> > consistent overall design with interchangeable and reusable code.

> Is this an officially proposed extension?

No, not officially.  The rvalue reference upon which it is based /is/ an
officially proposed extension:

http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2004/n1690.html

And unique_ptr is mentioned as a motivating example in the proposal
(actually in the supporting paper N1377), but is called move_ptr
instead, and isn't as fully fleshed out, e.g. no array specialization.
As momentum for the rvalue reference (hopefully) gains, I will
officially propose unique_ptr (or move_ptr or whatever we can agree on
to call it).

-Howard

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Howard Hinnant wrote:
> I surely hope that it is not impossible to resolve this issue.  If
> enough non-vendors weigh in, and happen to show a preponderance of
> support for one of the options, then I'm sure vendors will come
around.
> Vendors exist to serve their customers, else they will end up with
none.

Indeed, but if issue 431 is not resolved then vendors need not do
anything. I think one of the solutions needs to be chosen then vendors
can decide whether or not they will conform. I am not sure that looking
to vendors is the right way to solve this issue. Shouldn't the
committee decide which way is best?

I realise that it is handy to have a reference implementation when
suggesting a way to do but this should not be a problem if there is a
vendor for each approach.

> > > http://home.twcny.rr.com/hinnant/cpp_extensions/unique_ptr.html
> > > With such a smart pointer, allocators can become deleters with an
> > > appropriate adaptor.  Therefore there is more than just an
analogy
> > > between allocators and deleters.  There is an opportunity for a
> > > consistent overall design with interchangeable and reusable code.
> The rvalue reference upon which it is based /is/ an
> officially proposed extension:
>
> http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2004/n1690.html

This is very interesting but I think approaches 1, 2 or 3 could be used
to resolve 431 without this. I agree that this is helpful wrt
allocators but I would like to see 431 resolved before n1690 is done.
$0.02.

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In article <1104925442.568154.93370@z14g2000cwz.googlegroups.com>,
 apm35@student.open.ac.uk wrote:

> Shouldn't the
> committee decide which way is best?

Absolutely.  And the committee can be influenced by your opinion.

> > > > http://home.twcny.rr.com/hinnant/cpp_extensions/unique_ptr.html
> > > > With such a smart pointer, allocators can become deleters with an
> > > > appropriate adaptor.  Therefore there is more than just an
> analogy
> > > > between allocators and deleters.  There is an opportunity for a
> > > > consistent overall design with interchangeable and reusable code.
> > The rvalue reference upon which it is based /is/ an
> > officially proposed extension:
> >
> > http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2004/n1690.html
>
> This is very interesting but I think approaches 1, 2 or 3 could be used
> to resolve 431 without this.

Right.  I brought it up only to show that this issue goes beyond
containers and their allocators.  A solution consistent with anticipated
smart pointers and their deleters would be best.

-Howard

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Hello,

Does anyone know what progress has been made on issue 431 (unequal
allocators)? I  see from
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2004/n1599.html that
several possibilities have been presented. I am interested in knowing
which way, if any, the stds committee are leaning.
Regards,

Andrew Marlow

---
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In article <1103894340.612771.137220@z14g2000cwz.googlegroups.com>,
 apm35@student.open.ac.uk wrote:

> Hello,
>
> Does anyone know what progress has been made on issue 431 (unequal
> allocators)? I  see from
> http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2004/n1599.html that
> several possibilities have been presented. I am interested in knowing
> which way, if any, the stds committee are leaning.

To the best of my knowledge, the subject has not been discussed in
committee since N1599 was written.  I anticipate that it will be a very
contentious issue among vendors, as each of the three options is
strongly supported by at least one vendor.

I would like to summarize option 3 with a succinct lemma:

Allocators own resources.  In the context of unequal allocators,
allocator state should stay with the resources it owns.  If resource
ownership is to be transferred elsewhere, allocator state should follow
the resource.

Follow on lemma:  Allocator (state) should never be asked to deallocate
a resource which it did not allocate (does not own).

This follow on has implications for list::splice where it is possible
for a single list to own resources allocated by different allocators.
Such a situation must be made impossible for unequal allocators.

Such theory is not limited to containers and their allocators.  Smart
pointers which have both a "deleter", and transfer pointer ownership
from one instance to another, should also have deleter state follow the
pointer that it is responsible for.

http://home.twcny.rr.com/hinnant/cpp_extensions/unique_ptr.html

With such a smart pointer, allocators can become deleters with an
appropriate adaptor.  Therefore there is more than just an analogy
between allocators and deleters.  There is an opportunity for a
consistent overall design with interchangeable and reusable code.

By its very nature, shared_ptr already takes care of this problem.  The
pointer and the deleter are an inseparable unit after construction, even
through copying, assignment, swap and reset.

-Howard

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