220 24119 <678fc289-199f-425c-bdad-3499190d770f@isocpp.org> 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? 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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:24119 Archived-At: ------=_Part_1007_1303576077.1454385813139 Content-Type: multipart/alternative; boundary="----=_Part_1008_477889584.1454385813140" ------=_Part_1008_477889584.1454385813140 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 ts1, CheckString ts2, CheckString arg1, CheckString=20 arg2) { } //#case 1 template auto test(TS&&... ts1) { 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)...) }; } //case 3 template auto test(TS&&... ts1) { //C3260: '<': skipping unexpected token(s) before lambda body // lambda type capture can??=20 return[&ts1...](auto&&... args) mutable { return f(std::forward(ts1)..., std::forward(args)...) }; } 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 } Something seems to be possible also for other purposes, a variety of uses. 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 12=EC=8B=9C 21=EB=B6=84 25=EC=B4=88 UTC+9, Thiago Macieira =EB=8B= =98=EC=9D=98 =EB=A7=90: > > On Monday 01 February 2016 17:53:44 =EC=9C=A4=ED=9B=88=EB=82=A8 wrote:=20 > > for example)=20 > >=20 > > std::string f(std::string, std::string, std::string, std::string, int,= =20 > int,=20 > > float) {=20 > > }=20 > >=20 > > template=20 > > auto test(TS&&... ts1) {=20 > > auto fn =3D [&ts1...](auto&&... args) mutable {=20 > > return f(std::forward(ts1)...,=20 > std::forward(args)...);=20 > > };=20 > return fn; // was missing=20 > > }=20 > > Why do you need the in the lambda declaration? This example works= =20 > without it.=20 > > Can you give a concrete example of where this would be needed? Not=20 > something=20 > that shows how this could be used if it existed, but something that shows= =20 > how=20 > it solves a problem that was either not solved before or wasn't as easy t= o=20 > solve.=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_1008_477889584.1454385813140 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
#include <iostream>
#include <stri= ng>
// Move or Copy Check
struct CheckString {
=
std::= string data_{ "hello" };
CheckString() =3D default;
CheckString(c= onst CheckString& rhs) : data_{ rhs.data_ } {
std::cout << "= ;copying\n";
}

CheckString(CheckString&& rhs) := data_{ std::move(rhs.data_) } {
std::cout << "moving\n";<= /div>
= }
};

void f(CheckString ts1, CheckString= ts2, CheckString arg1, CheckString arg2) {
}

//#case 1
template<typename... TS>
auto tes= t(TS&&... ts1) {
return =C2=A0[&ts1...](auto&&... args)= mutable {
// error 'TS': parameter pack must be expanded in this = context
= // TS type not capture. just value capture.
return f(std::forwar= d<TS>(ts1)..., std::forward<decltype(args)>(args)...)
};
<= div>}

//case 2
template<typename... T= S>
auto test(TS&&... ts1) {
//error syntax error: miss= ing ']' before '=3D'
// forward to lambda capture--> usi= ng in lambda body
return[ts...=3D std::forward<TS>(ts1)...](auto&= &... args) mutable {
return f(ts..., std::forward<decltype(args)>= ;(args)...)
};
}

//case 3
temp= late<typename... TS>
auto test(TS&&... ts1) {
=
//C32= 60: '<': skipping unexpected token(s) before lambda body
// lamb= da type capture can??
return[&ts1...]<TS...>(auto&&... args) mutabl= e {
return f(std::forward<TS>(ts1)..., std::forward<decltype(args= )>(args)...)
};
}

int main() {
<= div> CheckS= tring ts1, ts2, arg1, arg2;
auto fn =3D test(ts1, std::move(ts2));
fn(arg1= , std::move(arg2));
// ts2, arg2 ->moving
// ts1, arg1 ->copying
}

Something seems to be possible also for = other purposes, a variety of uses.

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 12=EC=8B=9C 21=EB= =B6=84 25=EC=B4=88 UTC+9, Thiago Macieira =EB=8B=98=EC=9D=98 =EB=A7=90:On Monday 01 February 2016 17:53:4= 4 =EC=9C=A4=ED=9B=88=EB=82=A8 wrote:
> for example)
>=20
> std::string f(std::string, std::string, std::string, std::string, = int, int,
> float) {
> }
>=20
> template<typename... TS>
> auto test(TS&&... ts1) {
> auto fn =3D [&ts1...]<TS...>(auto&&... args) mut= able {
> return f(std::forward<TS>(ts1)..., std::forward<decltype(= args)>(args)...);
> };
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0return fn;=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0// was missing
> }

Why do you need the <TS...> in the lambda declaration? This examp= le works=20
without it.

Can you give a concrete example of where this would be needed? Not some= thing=20
that shows how this could be used if it existed, but something that sho= ws how=20
it solves a problem that was either not solved before or wasn't as = easy to=20
solve.

--=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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