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[209.85.220.41]) by mx.google.com with SMTPS id x14-v6sor6756484ljh.27.2018.10.26.01.00.40 for (Google Transport Security); Fri, 26 Oct 2018 01:00:40 -0700 (PDT) Received-SPF: pass (google.com: domain of gasper.azman@gmail.com designates 209.85.220.41 as permitted sender) client-ip=209.85.220.41; X-Received: by 2002:a2e:81d3:: with SMTP id s19-v6mr1433579ljg.138.1540540839877; Fri, 26 Oct 2018 01:00:39 -0700 (PDT) In-Reply-To: X-Original-Sender: gasper.azman@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=U4B8MdLW; spf=pass (google.com: domain of gasper.azman@gmail.com designates 209.85.220.41 as permitted sender) smtp.mailfrom=gasper.azman@gmail.com; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: X-Spam-Checked-In-Group: std-proposals@isocpp.org X-Google-Group-Id: 399137483710 List-Post: , List-Help: , List-Archive: List-Subscribe: , List-Unsubscribe: , Xref: news.gmane.org gmane.comp.lang.c++.isocpp.proposals:40763 Archived-At: --00000000000085e26b05791d1d63 Content-Type: text/plain; charset="UTF-8" Differences: void foo(T* x); observer_ptr p: optional opt; foo(p.get()); foo(opt?&*opt:nullptr); plus, the hashing on observer pointers is the hash of the pointer value, and in the case where I want a set of unique optional object references I have to specify my own hash on the `&*opt`s again. Basically, despite the fact that there is a bijection, they are not equivalent in usage. We can very well have both, with good guidelines on when to use each, and perhaps two-way conversions to boot. G On Fri, Oct 26, 2018 at 10:40 AM Miguel Ojeda < miguel.ojeda.sandonis@gmail.com> wrote: > On Thu, Oct 25, 2018 at 10:59 PM Ville Voutilainen > wrote: > > > > On Thu, 25 Oct 2018 at 23:31, Miguel Ojeda > > wrote: > > > > I can always get the pointer value from an observer_ptr. I can't get a > > value from an optional when it has none. > > [Forgot to reply to this] > > That, again, is *no* difference. You can create a two-way function > that maps empty optional to a nullptr. The only cases which would > be impossible to represent with an optional are all the > non-nullptr & non-valid pointers/addresses, which is what I said in > the beginning and Tony replied to. Again: the nullptr case is not one > of those. > > Cheers, > Miguel > > -- > You received this message because you are subscribed to the Google Groups > "ISO C++ Standard - Future Proposals" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to std-proposals+unsubscribe@isocpp.org. > To post to this group, send email to std-proposals@isocpp.org. > To view this discussion on the web visit > https://groups.google.com/a/isocpp.org/d/msgid/std-proposals/CANiq72kOHDe28rHekVQ9Ov%2BOuXZ2wMnH-CQ__PRD4%2BnB_pLAEw%40mail.gmail.com > . > -- You received this message because you are subscribed to the Google Groups "ISO C++ Standard - Future Proposals" group. To unsubscribe from this group and stop receiving emails from it, send an email to std-proposals+unsubscribe@isocpp.org. To post to this group, send email to std-proposals@isocpp.org. To view this discussion on the web visit https://groups.google.com/a/isocpp.org/d/msgid/std-proposals/CAANG%3DkVVCnTpCRkFaG2X0%3DjYaDvQLDm7SDQT3WkTxXHktTXn0g%40mail.gmail.com. --00000000000085e26b05791d1d63 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
Differences:

void foo(T* x);
=
observer_ptr<T> p:
optional<T&> op= t;

foo(p.get());
foo(opt?&*opt:nullp= tr);

plus, the hashing on observer pointers is the= hash of the pointer value, and in the case where I want a set of unique op= tional object references I have to specify my own hash on the `&*opt`s = again.

Basically, despite the fact that there is a= bijection, they are not equivalent in usage. We can very well have both, w= ith good guidelines on when to use each, and perhaps two-way conversions to= boot.

G


On Fri, Oct 26, 2018 at 10:40 AM Miguel O= jeda <miguel.ojeda.sa= ndonis@gmail.com> wrote:
On = Thu, Oct 25, 2018 at 10:59 PM Ville Voutilainen
<ville.= voutilainen@gmail.com> wrote:
>
> On Thu, 25 Oct 2018 at 23:31, Miguel Ojeda
> <miguel.ojeda.sandonis@gmail.com> wrote:
>
> I can always get the pointer value from an observer_ptr. I can't g= et a
> value from an optional<T&> when it has none.

[Forgot to reply to this]

That, again, is *no* difference. You can create a two-way function
that maps empty optional<T&> to a nullptr. The only cases which w= ould
be impossible to represent with an optional<T&> are all the
non-nullptr & non-valid pointers/addresses, which is what I said in
the beginning and Tony replied to. Again: the nullptr case is not one
of those.

Cheers,
Miguel

--
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