Implementation issue `forward auto` fails to compile

[aminya]

Thanks for this great proposal!

I was trying this at https://cppx.godbolt.org. I faced this issue that forward auto does not compile:

https://cppx.godbolt.org/z/ezPz7K

#include <iostream>
using namespace std;

auto myfun(in auto x, forward auto y) {
    cout << x << endl;
    y = "goodbye";
    auto z = 0;
    return tuple{y, z};
}


int main() {
    auto [y, z] = myfun(1, string("hey"));
    cout << y <<endl;
    cout << z;
}

Error log

<source>:13:19: error: no matching function for call to 'myfun'

    auto [y, z] = myfun(1, string("hey"));

                  ^~~~~

<source>:4:6: note: candidate ignored; expected deduced type 'auto' but got 'std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>'

auto myfun(in auto x, forward auto y) {

     ^

1 error generated.

ASM generation compiler returned: 1

<source>:13:19: error: no matching function for call to 'myfun'

    auto [y, z] = myfun(1, string("hey"));

                  ^~~~~

<source>:4:6: note: candidate ignored; expected deduced type 'auto' but got 'std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>'

auto myfun(in auto x, forward auto y) {

     ^

1 error generated.

Execution build compiler returned: 1

In comparison this compiles:
https://cppx.godbolt.org/z/66YbnT

#include <iostream>
using namespace std;

auto myfun(in auto x, forward string y) {
    cout << x << endl;
    y = "goodbye";
    auto z = 0;
    return tuple{y, z};
}


int main() {
    auto [y, z] = myfun(1, string("hey"));
    cout << y <<endl;
    cout << z;
}

or this
https://cppx.godbolt.org/z/q64YfP

#include <iostream>
using namespace std;

auto myfun(auto x, auto &&y) {
    cout << x << endl;
    y = "goodbye";
    auto z = 0;
    return tuple{y, z};
}


int main() {
    auto [y, z] = myfun(1, string("hey"));
    cout << y <<endl;
    cout << z;
}

Feel free to transfer this issue to the proper repository that contains the actual implementation.

[hsutter]

Thanks, and sorry for the lag. #14 captures that the implementation of forward generally is not yet complete. . This issue is more than a duplicate of 14 so I'll leave it open as well. Both issues should be fixed when forward is completed. Thanks!