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[209.85.220.65]) by mx.google.com with SMTPS id j185sor25940pgc.286.2018.03.13.04.26.44 for (Google Transport Security); Tue, 13 Mar 2018 04:26:44 -0700 (PDT) Received-SPF: pass (google.com: domain of gasper.azman@gmail.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; X-Received: by 10.99.122.80 with SMTP id j16mr207021pgn.5.1520940403903; Tue, 13 Mar 2018 04:26:43 -0700 (PDT) Original-Received: by 10.236.133.141 with HTTP; Tue, 13 Mar 2018 04:26:23 -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=knohT2F9; spf=pass (google.com: domain of gasper.azman@gmail.com designates 209.85.220.65 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:37320 Archived-At: --f403045c5a2a7fd11405674988bb Content-Type: text/plain; charset="UTF-8" But my point was we *already have* an operator with the exact semantics of the macro above - it's just a gnu extension. We could just propose that! https://gcc.gnu.org/onlinedocs/gcc/Conditionals.html x = x?:new int; It's unambiguous, it's obvious it's a conditional, it's a one-liner, and more importantly, it can be used for way more than just pointers. Oh, and we have implementations and knowledge of how it behaves, and it's also not a weird new form of || or |. It also fails to compile if "x" and the expression if x is falsy don't have a common type, which is *also* important. So, I'd encourage the author of this proposal to instead propose the gnu extension as an actual feature, instead of trying to fit a "don't evaluate this" model as a special case for just certain types - making user-defined types less like built-in types is an explicit no-no these days, and this proposal is just trying to special-case pointers. G On Mon, Mar 12, 2018 at 11:41 AM, Miguel Ojeda < miguel.ojeda.sandonis@gmail.com> wrote: > On Mon, Mar 12, 2018 at 11:42 AM, Richard Hodges > wrote: > > > > Consider: > > > > p |= new_thing(); > > > > In the above code, do we mean that we wish to replace p with a new thing > if > > empty, or does it mean that we wish to merge a new thing into the object > > referenced by p? > > For me ||= would be the replace. But since we don't have ||=, I just > picked |=, which indeed looks fishy. > > Now, what would be a nice experiment would be ||, &&, ||= and &&= with > short-circuit semantics, which could be implemented if we had the > "expression E" stuff: > > template > operator||=(T & t, E) > { > if (t) > return; > t = E; > } > > Then: > > x ||= new int; > > would have the expected results. > > 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/CANiq72kNstxnyLTCOBfNorEiyudTi > jCAUHwH4DsoT14WqcNs4w%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%3DkWjgCt-%2BpKOwWk6BgwNZ9ZECd9twWwq_FC1f3WPEiNw%3DA%40mail.gmail.com. --f403045c5a2a7fd11405674988bb Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
But my point was we *already have* an operator with the ex= act semantics of the macro above - it's just a gnu extension. We could = just propose that!


x =3D x?= :new int;

It's unambiguous, it's obvious i= t's a conditional, it's a one-liner, and more importantly, it can b= e used for way more than just pointers. Oh, and we have implementations and= knowledge of how it behaves, and it's also not a weird new form of || = or |.

It also fails to compile if "x" an= d the expression if x is falsy don't have a common type, which is *also= * important.

So, I'd encourage the author of t= his proposal to instead propose the gnu extension as an actual feature, ins= tead of trying to fit a "don't evaluate this" model as a spec= ial case for just certain types - making user-defined types less like built= -in types is an explicit no-no these days, and this proposal is just trying= to special-case pointers.

G

<= /div>

On Mon, Mar = 12, 2018 at 11:41 AM, Miguel Ojeda <miguel.ojeda.sandonis@gm= ail.com> wrote:
On Mon, Mar 12, 2018 at 11:42 AM, Richard Hodges <hodges.r@gmail.com> wrote:
>
> Consider:
>
> p |=3D new_thing();
>
> In the above code, do we mean that we wish to replace p with a new thi= ng if
> empty, or does it mean that we wish to merge a new thing into the obje= ct
> referenced by p?

For me ||=3D would be the replace. But since we don't have ||=3D= , I just
picked |=3D, which indeed looks fishy.

Now, what would be a nice experiment would be ||, &&, ||=3D and &am= p;&=3D with
short-circuit semantics, which could be implemented if we had the
"expression E" stuff:

=C2=A0 =C2=A0 template <typename T, expression E>
=C2=A0 =C2=A0 operator||=3D(T & t, E)
=C2=A0 =C2=A0 {
=C2=A0 =C2=A0 =C2=A0 =C2=A0 if (t)
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 return;
=C2=A0 =C2=A0 =C2=A0 =C2=A0 t =3D E;
=C2=A0 =C2=A0 }

Then:

=C2=A0 =C2=A0 x ||=3D new int;

would have the expected results.

Cheers,
Miguel

--
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--
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