220 40285 <6d2bdffd-187d-44e7-90b2-4c158ee19fe4@isocpp.org> article Path: news.gmane.org!.POSTED!not-for-mail From: Adrian H Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: std::between ? 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Tue, 02 Oct 2018 08:31:34 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 2002:a81:8706:: with SMTP id x6-v6ls6546636ywf.10.gmail; Tue, 02 Oct 2018 08:31:33 -0700 (PDT) X-Received: by 2002:a81:78c6:: with SMTP id t189-v6mr168958ywc.7.1538494293240; Tue, 02 Oct 2018 08:31:33 -0700 (PDT) In-Reply-To: <952795b3-b87b-4140-b4f2-2c9ad968b2f7@isocpp.org> X-Original-Sender: adrian.hawryluk@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:40285 Archived-At: ------=_Part_282_985702005.1538494292518 Content-Type: multipart/alternative; boundary="----=_Part_283_927077165.1538494292518" ------=_Part_283_927077165.1538494292518 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Friday, September 28, 2018 at 6:47:14 PM UTC-4, Adrian H wrote: > > On Friday, September 28, 2018 at 11:25:30 AM UTC-4, Daniel Gutson wrote:= =20 > > El vie., 28 de sep. de 2018 a la(s) 12:18, Adrian H ( > adrian....@gmail.com) escribi=C3=B3:=20 > >=20 > > #include =20 > > #include =20 > >=20 > >=20 > > template=20 > > struct chain_impl {=20 > > chain_impl(T&& obj, bool val) : obj(std::move(obj)), val(val) {}=20 > > T&& obj;=20 > > bool val;=20 > > explicit operator bool() {=20 > > return val;=20 > > }=20 > > };=20 > >=20 > >=20 > > template=20 > > struct chain_impl {=20 > > chain_impl(T& obj, bool val) : obj(obj), val(val) {}=20 > > T& obj;=20 > > bool val;=20 > > explicit operator bool() {=20 > > return val;=20 > > }=20 > > };=20 > >=20 > >=20 > > template =20 > > decltype(auto) make_chain(T&& obj, bool val =3D true) {=20 > > return=20 > chain_impl::value, T&,=20 > T&&>>(std::forward(obj), val);=20 > > }=20 > >=20 > >=20 > > template =20 > > auto operator< (chain_impl&& lhs, T1&& rhs) {=20 > > if (lhs.val) {=20 > >=20 > >=20 > > Why you say that comparisons are performed? You are breaking the chain= =20 > here with this evaluation. So yes, operator will keep be called, but it's= =20 > just this if.=20 > > So maybe not a comparison, but still a flag check for each comparison,=20 > regardless if it reached a potential short circuit point. Also, an extra= =20 > Boolean would be needed to be allocated for each term.=20 > > Unless you're saying that the optimizer will be able to detect this and= =20 > short circuit the operation and not allocate the Booleans? That would be= =20 > nice, but I don't have that much faith in the optimizer. So unless it can= =20 > optimize that code and data away then this feature would have to be on th= e=20 > compiler level so as not to add extra crap to the final binary.=20 > > Wow. I take it back. The optimizer seems more than capable of removing=20 all of the cruft. gcc 8.2 output: https://godbolt.org/z/DecqoQ shows that there doesn't seem to be any boolean mid term storage and short= =20 circuiting does appear to be happening. I'm really impressed. Evan MS VC++ 2017 doesn't do too bad of a job. Though it does leave a=20 bunch of unnecessary code in the binary, it doesn't actually execute it. = =20 https://godbolt.org/z/N58hN4 Truly impressive. Seems that there is really no need for this feature=20 after all. A --=20 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 e= mail 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/6d2bdffd-187d-44e7-90b2-4c158ee19fe4%40isocpp.or= g. ------=_Part_283_927077165.1538494292518 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
On Friday, September 28, 2018 at 6:47:14 PM UTC-4, Adrian = H wrote:
On Friday, September 2= 8, 2018 at 11:25:30 AM UTC-4, Daniel Gutson wrote:
> El vie., 28 de sep. de 2018 a la(s) 12:18, Adrian H (adrian....= @gmail.com) escribi=C3=B3:
>=20
> #include <iostream>
> #include <type_traits>
>=20
>=20
> template<typename T>
> struct chain_impl {
> =C2=A0 chain_impl(T&& obj, bool val) : obj(std::move(obj))= , val(val) {}
> =C2=A0 T&& obj;
> =C2=A0 bool val;
> =C2=A0 explicit operator bool() {
> =C2=A0 =C2=A0 =C2=A0 return val;
> =C2=A0 }
> };
>=20
>=20
> template<typename T>
> struct chain_impl<T&> {
> =C2=A0 chain_impl(T& obj, bool val) : obj(obj), val(val) {}
> =C2=A0 T& obj;
> =C2=A0 bool val;
> =C2=A0 explicit operator bool() {
> =C2=A0 =C2=A0 =C2=A0 return val;
> =C2=A0 }
> };
>=20
>=20
> template <typename T>
> decltype(auto) make_chain(T&&=C2=A0 obj, bool val =3D true= ) {
> =C2=A0 return chain_impl<std::conditional_t<std::is_lva= lue_reference<T>::value, T&, T&&>>(std::forwar= d<T>(obj), val);
> }
>=20
>=20
> template <typename T0, typename T1>
> auto operator< (chain_impl<T0>&& lhs, T1&&= ; rhs) {
> =C2=A0 =C2=A0 if (lhs.val) {
>=20
>=20
> Why you say that comparisons are performed? You are breaking the c= hain here with this evaluation. So yes, operator will keep be called, but i= t's just this if.

So maybe not a comparison, but still a flag check for each comparison, = regardless if it reached a potential short circuit point. Also, an extra Bo= olean would be needed to be allocated for each term.

Unless you're saying that the optimizer will be able to detect this= and short circuit the operation and not allocate the Booleans? That would = be nice, but I don't have that much faith in the optimizer. So unless i= t can optimize that code and data away then this feature would have to be o= n the compiler level so as not to add extra crap to the final binary.


Wow.=C2=A0 I take it back.=C2=A0 The o= ptimizer seems more than capable of removing all of the cruft. gcc 8.2 outp= ut:

https://godbolt.org/z/DecqoQ

shows that there doesn't seem to be any boolean mid term storag= e and short circuiting does appear to be happening.=C2=A0 I'm really im= pressed.

Evan MS VC++ 2017 doesn't do too bad = of a job.=C2=A0 Though it does leave a bunch of unnecessary code in the bin= ary, it doesn't actually execute it.=C2=A0 https://godbolt.org/z/N58hN4=

Truly impressive.=C2=A0 Seems that there is reall= y no need for this feature after all.


A

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