220 24128 article Path: news.gmane.org!not-for-mail From: =?UTF-8?B?7Jyk7ZuI64Ko?= Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: lambda template? Date: Mon, 1 Feb 2016 23:40:05 -0800 (PST) Lines: 284 Approved: news@gmane.org Message-ID: References: <64578f60-f8cf-4fdf-91c2-9df72e9dfe09@isocpp.org> <3943320.mcaVf4CF4p@tjmaciei-mobl4> <678fc289-199f-425c-bdad-3499190d770f@isocpp.org> <53952014.4UIbchGS4l@tjmaciei-mobl4> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_2344_1101567846.1454398806092" X-Trace: ger.gmane.org 1454398816 10972 80.91.229.3 (2 Feb 2016 07:40:16 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Tue, 2 Feb 2016 07:40:16 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBD4LVQW26ICBBVV2YG2QKGQEMZASHPA@isocpp.org Tue Feb 02 08:40:11 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ig0-f199.google.com ([209.85.213.199]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1aQVZI-0004tu-RZ for gclcip-std-proposals@m.gmane.org; Tue, 02 Feb 2016 08:40:09 +0100 Original-Received: by mail-ig0-f199.google.com with SMTP id ik10sf17100240igb.2 for ; Mon, 01 Feb 2016 23:40:08 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:message-id:in-reply-to:references:subject:mime-version :content-type:x-original-sender:reply-to:precedence:mailing-list :list-id:x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=XKvXlCeiMWx/yMyuH6gCsJax7lytZKALRRppZGmwd3M=; b=1DKcU43AgFYW68t0KtvSdv7ALFXYYuJJz8d5Zslvf5LDlp8b/C/PKZ2FaUwyR43JE3 RPP6DQlqzOlk8mrVNv1u9b0YOC7rGOW6U0T3sXgX34vWkZLH/TlK0Efd5QJZasGSXCx7 GzqPFGKKiJhk+JrqgRToopRg72GR0BRKicopt+zmgzvI/S9mO9L3U/FJcivi1ZpWMfk7 8CdGba6MxKquEgo5hyucbQOcSw5oIn33Mgr1TZSw8tRetdCtibEithDu17t95saFhdtp +6DcKRONkQtZul8s7i2wQ3QPmC1fs/pztNYgB+KvX3RogP7MOWok+Beqqv77En1paEnk AAww== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:date:from:to:message-id:in-reply-to:references :subject:mime-version:content-type:x-original-sender:reply-to :precedence:mailing-list:list-id:x-spam-checked-in-group:list-post :list-help:list-archive:list-subscribe:list-unsubscribe; bh=XKvXlCeiMWx/yMyuH6gCsJax7lytZKALRRppZGmwd3M=; b=HO/4JOTr8vRx2GIZ33xsZRKTCHhWF9HPxqNQlbDRMQvkV1Q+8UECRLNhb8E52yE54N m7rQmhUJRjBiWbmvTarawSzpzpmQAf7uOOMNuCW3b7ASztoJnN06RkQrifkcWaxU5v9i N64HCssaJviJZTMoSUITMExRd7O4Znzv1yTO9qYcdqcRlpyzmQxkq0F2wuyXcKZ5QwTj R308X2/PjlKIbBDcrrRZoqeGu0hIQPFn3jLrrNYZoAcBrbXDTXBhYwK6/Hh9buGUbUEl UMzQxBax3uupHPX6Oo4uPsc9UA3nHsk/QDMtMuKjKnjh3PUab9QiFCKFeQPgd8PHF3S6 Xrpg== X-Gm-Message-State: AG10YOSlUfiyNu0G/Bw2UAk/WvWkY17VxyiEU1OsFTJouJPkctYsgD1rnpm7HvwVoJ3O5Q== X-Received: by 10.182.112.233 with SMTP id it9mr28634212obb.45.1454398807746; Mon, 01 Feb 2016 23:40:07 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.107.128.69 with SMTP id b66ls114777iod.101.gmail; Mon, 01 Feb 2016 23:40:06 -0800 (PST) X-Received: by 10.50.41.5 with SMTP id b5mr312268igl.8.1454398806640; Mon, 01 Feb 2016 23:40:06 -0800 (PST) In-Reply-To: <53952014.4UIbchGS4l@tjmaciei-mobl4> X-Original-Sender: sim9108@naver.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:24128 Archived-At: ------=_Part_2344_1101567846.1454398806092 Content-Type: multipart/alternative; boundary="----=_Part_2345_2103080339.1454398806093" ------=_Part_2345_2103080339.1454398806093 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable #include #include // Move or Copy Check struct CheckString { std::string data_{ "hello" }; CheckString() =3D default; CheckString(const CheckString& rhs) : data_{ rhs.data_ } { std::cout << "copying\n"; } CheckString(CheckString&& rhs) : data_{ std::move(rhs.data_) } { std::cout << "moving\n"; } }; void f(CheckString a, CheckString b, CheckString c, CheckString d) { } //#case 1 template auto test(TS&&... ts1) { =20 return [&ts1...](auto&&... args) mutable { // error 'TS': parameter pack must be expanded in this context // TS type not capture. just value capture. return f(std::forward(ts1)..., std::forward(args)...); }; } //case 2 template auto test(TS&&... ts1) { //error syntax error: missing ']' before '=3D' // forward to lambda capture--> using in lambda body return[ts...=3D std::forward(ts1)...](auto&&... args) mutable { return f(ts..., std::forward(args)...); }; } // make_lambda function auto make_lamba(){ CheckString ts1, ts2; return test(ts1, std::move(ts2)); } int main() { CheckString arg1, arg2; auto fn =3Dmake_lamba(); fn(arg1, std::move(arg2)); //print error; } In the case of the case 1, ts1 is simply a reference. Therefore, depending on the time the call is at risk. That incomplete forwarding case 2 is captured by an explicit forwarding. 2016=EB=85=84 2=EC=9B=94 2=EC=9D=BC =ED=99=94=EC=9A=94=EC=9D=BC =EC=98=A4= =ED=9B=84 3=EC=8B=9C 33=EB=B6=84 24=EC=B4=88 UTC+9, Thiago Macieira =EB=8B= =98=EC=9D=98 =EB=A7=90: > > On Monday 01 February 2016 20:03:32 =EC=9C=A4=ED=9B=88=EB=82=A8 wrote:=20 > > #include =20 > > #include =20 > > // Move or Copy Check=20 > > struct CheckString {=20 > > std::string data_{ "hello" };=20 > > CheckString() =3D default;=20 > > CheckString(const CheckString& rhs) : data_{ rhs.data_ } {=20 > > std::cout << "copying\n";=20 > > }=20 > >=20 > > CheckString(CheckString&& rhs) : data_{ std::move(rhs.data_) } {=20 > > std::cout << "moving\n";=20 > > }=20 > > };=20 > >=20 > > void f(CheckString ts1, CheckString ts2, CheckString arg1, CheckString= =20 > > arg2) {=20 > > }=20 > >=20 > > //#case 1=20 > > template=20 > > auto test(TS&&... ts1) {=20 > > return [&ts1...](auto&&... args) mutable {=20 > > // error 'TS': parameter pack must be expanded in this context=20 > > // TS type not capture. just value capture.=20 > > return f(std::forward(ts1)...,=20 > std::forward(args)...)=20 > > };=20 > > }=20 > > No error here, Clang 3.7, GCC 5.3, ICC 16.0.=20 > > > int main() {=20 > > CheckString ts1, ts2, arg1, arg2;=20 > > auto fn =3D test(ts1, std::move(ts2));=20 > > fn(arg1, std::move(arg2));=20 > > // ts2, arg2 ->moving=20 > > // ts1, arg1 ->copying=20 > > }=20 > >=20 > > Something seems to be possible also for other purposes, a variety of=20 > uses.=20 > > Please explain with words what this is supposed to do. And considering=20 > case 1=20 > works, why do we need cases 2 or 3?=20 > > --=20 > Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org=20 > Software Architect - Intel Open Source Technology Center=20 > PGP/GPG: 0x6EF45358; fingerprint:=20 > E067 918B B660 DBD1 105C 966C 33F5 F005 6EF4 5358=20 > > --=20 ---=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. Visit this group at https://groups.google.com/a/isocpp.org/group/std-propos= als/. ------=_Part_2345_2103080339.1454398806093 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
#include <iostream>
#include <stri= ng>
// Move or Copy Check
struct CheckString {
=
=C2=A0 =C2=A0 std::string data_{ "hello" };
CheckString() = =3D default;
CheckString(const CheckString& rhs) : data_{ rhs.data_ } {=
std::cout << "copying\n";
}

CheckString(Ch= eckString&& rhs) : data_{ std::move(rhs.data_) } {
std::cout <&= lt; "moving\n";
}
};

void f(Ch= eckString a, CheckString b, CheckString c, CheckString d) {
}

//#case 1
template<typename... TS>
auto test(TS&&... ts1) {
=C2=A0 =C2=A0=C2=A0
retu= rn =C2=A0[&ts1...](auto&&... args) mutable {
// error 'TS&= #39;: parameter pack must be expanded in this context
// TS type not captu= re. just value capture.
return f(std::forward<TS>(ts1)..., std::forw= ard<decltype(args)>(args)...);
};
}

//case 2
template<typename... TS>
auto tes= t(TS&&... ts1) {
//error syntax error: missing ']' before &= #39;=3D'
// forward to lambda capture--> using in lambda body
<= div> return= [ts...=3D std::forward<TS>(ts1)...](auto&&... args) mutable {=
return f(ts..., std::forward<decltype(args)>(args)...);
<= span class=3D"Apple-tab-span" style=3D"white-space:pre"> };
}

// make_lambda function
auto m= ake_lamba(){
=C2=A0 =C2=A0 CheckString ts1, ts2;
=C2=A0= =C2=A0 return test(ts1, std::move(ts2));
}

<= div>int main() {
CheckString arg1, arg2;
=C2=A0 =C2=A0 =C2=A0 =C2= =A0 auto fn =3Dmake_lamba();
fn(arg1, std::move(arg2)); //print error;
}

In the case of the case 1,
= ts1 is simply a reference.
Therefore, depending on the time the c= all is at risk.
That incomplete forwarding

case 2 is captured by an explicit forwarding.

=
2016=EB=85=84 2=EC=9B=94 2=EC=9D=BC =ED=99=94=EC=9A=94=EC=9D=BC =EC=98= =A4=ED=9B=84 3=EC=8B=9C 33=EB=B6=84 24=EC=B4=88 UTC+9, Thiago Macieira =EB= =8B=98=EC=9D=98 =EB=A7=90:
On M= onday 01 February 2016 20:03:32 =EC=9C=A4=ED=9B=88=EB=82=A8 wrote:
> #include <iostream>
> #include <string>
> // Move or Copy Check
> struct CheckString {
> std::string data_{ "hello" };
> CheckString() =3D default;
> CheckString(const CheckString& rhs) : data_{ rhs.data_ } {
> std::cout << "copying\n";
> }
>=20
> CheckString(CheckString&& rhs) : data_{ std::move(rhs.data= _) } {
> std::cout << "moving\n";
> }
> };
>=20
> void f(CheckString ts1, CheckString ts2, CheckString arg1, CheckSt= ring
> arg2) {
> }
>=20
> //#case 1
> template<typename... TS>
> auto test(TS&&... ts1) {
> return =C2=A0[&ts1...](auto&&... args) mutable {
> // error 'TS': parameter pack must be expanded in this con= text
> // TS type not capture. just value capture.
> return f(std::forward<TS>(ts1)..., std::forward<decltype(= args)>(args)...)
> };
> }

No error here, Clang 3.7, GCC 5.3, ICC 16.0.

> int main() {
> CheckString ts1, ts2, arg1, arg2;
> auto fn =3D test(ts1, std::move(ts2));
> fn(arg1, std::move(arg2));
> // ts2, arg2 ->moving
> // ts1, arg1 ->copying
> }
>=20
> Something seems to be possible also for other purposes, a variety = of uses.

Please explain with words what this is supposed to do. And considering = case 1=20
works, why do we need cases 2 or 3?

--=20
Thiago Macieira - thiago (AT) maciei= ra.info - thiago (AT) kde.org
=C2=A0 =C2=A0Software Architect - Intel Open Source Technology Center
=C2=A0 =C2=A0 =C2=A0 PGP/GPG: 0x6EF45358; fingerprint:
=C2=A0 =C2=A0 =C2=A0 E067 918B B660 DBD1 105C =C2=A0966C 33F5 F005 6EF4= 5358

--

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