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From: Jonathan Wakely <jwakely.gcc@gmail.com>
To: "François Dumont" <frs.dumont@gmail.com>
Cc: Jonathan Wakely <jwakely@redhat.com>,
	"libstdc++" <libstdc++@gcc.gnu.org>,
	 gcc-patches <gcc-patches@gcc.gnu.org>
Subject: Re: [committed] libstdc++: Specialize std::pointer_traits<__normal_iterator<I, C>>
Date: Mon, 4 Oct 2021 21:30:02 +0100	[thread overview]
Message-ID: <CAH6eHdTFjVv=q10Qe4Y+LOnOmcOTqeCBFROjaOpXWKN4dH8xKQ@mail.gmail.com> (raw)
In-Reply-To: <34b34b00-8c96-68c1-e436-ab0f64291c2f@gmail.com>

On Mon, 4 Oct 2021 at 21:28, François Dumont via Libstdc++
<libstdc++@gcc.gnu.org> wrote:
>
> On 04/10/21 10:05 pm, François Dumont wrote:
> > On 02/10/21 10:24 pm, Jonathan Wakely wrote:
> >> On Sat, 2 Oct 2021 at 18:27, François Dumont wrote:
> >>> I would like to propose this alternative approach.
> >>>
> >>> In this patch I make __normal_iterator and random iterator
> >>> _Safe_iterator compatible for pointer_traits primary template.
> >>>
> >>> Regarding pointer_traits I wonder if it shouldn't check for the
> >>> to_pointer method availability and use per default: return {
> >>> std::addressof(__e) }; otherwise. This way we wouldn't have to
> >>> provide a
> >>> pointer_to method on __normal_iterator.
> >> But I would rather not have these members present in vector::iterator
> >> and string::iterator, in case users accidentally start to rely on them
> >> being present.
> >
> > Making pointer_traits friends would help but I do not like it neither.
> >
> >
> >>
> >> Another option would be to overload std::__to_address so it knows how
> >> to get the address from __normal_iterator and _Safe_iterator.
> >>
> >> .
> >
> > I start thinking that rather than proposing not-useful and even
> > incorrect code in the case of the _Safe_iterator<> it might be a
> > better approach.
> >
> > Even the rebind for __normal_iterator is a little strange because when
> > doing rebind on std::vector<int>::iterator for long it produces
> > __normal_iterator<long*, std::vector<int>>, quite inconsistent even if
> > useless.
> >
> > But there's something that I'm missing, what is the relation between
> > __addressof and std::pointer_traits ? Is it that __builtin_addressof
> > is using it ?
> >
> Ignore this last question, I realized that we are talking about
> __to_address, not __addressof.

Yes, see the definition of std::__to_address in <bits/ptr_traits.h>
and also PR 96416.

  reply	other threads:[~2021-10-04 20:30 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-28 19:25 [committed] libstdc++: Specialize std::pointer_traits<__normal_iterator<I,C>> Jonathan Wakely
2021-09-30 20:24 ` François Dumont
2021-10-01 22:29   ` [committed] libstdc++: Specialize std::pointer_traits<__normal_iterator<I, C>> Jonathan Wakely
2021-10-02 13:08     ` [committed] libstdc++: Specialize std::pointer_traits<__normal_iterator<I,C>> François Dumont
2021-10-02 20:28       ` [committed] libstdc++: Specialize std::pointer_traits<__normal_iterator<I, C>> Jonathan Wakely
2021-10-02 17:27     ` [committed] libstdc++: Specialize std::pointer_traits<__normal_iterator<I,C>> François Dumont
2021-10-02 20:24       ` [committed] libstdc++: Specialize std::pointer_traits<__normal_iterator<I, C>> Jonathan Wakely
2021-10-04 20:05         ` [committed] libstdc++: Specialize std::pointer_traits<__normal_iterator<I,C>> François Dumont
2021-10-04 20:26           ` François Dumont
2021-10-04 20:30             ` Jonathan Wakely [this message]
2021-10-06 17:18               ` François Dumont
2021-10-06 17:25                 ` François Dumont
2021-12-14  6:53                   ` François Dumont
2021-12-14 13:12                     ` [committed] libstdc++: Specialize std::pointer_traits<__normal_iterator<I, C>> Jonathan Wakely
2021-12-15 21:16                       ` [committed] libstdc++: Specialize std::pointer_traits<__normal_iterator<I,C>> François Dumont
2021-12-15 21:21                         ` [committed] libstdc++: Specialize std::pointer_traits<__normal_iterator<I, C>> Jonathan Wakely

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