[Bug c++/82619] C++17 std::apply treated as in global namespace under certain circumstances

[tower120 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82619

tower120 <tower120 at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|WAITING                     |RESOLVED
         Resolution|---                         |INVALID

--- Comment #4 from tower120 <tower120 at gmail dot com> ---
Sorry, this is ADL indeed.

I just noticed, that I tested in other compilers with -std=C++14 flag. That's
why that worked in all other compilers and pre gcc7.


Now, being aware of ADL, I am able to make the shortest version of "bug":

#include <tuple>

namespace ns {
    template<class F, class Tuple, std::size_t... I>
    static constexpr decltype(auto) apply_impl(F &&f, Tuple &&t,
std::index_sequence<I...>) {
        return f(std::get<I>(std::forward<Tuple>(t))...);
    }

    template<class F, class Tuple>
    static constexpr decltype(auto) apply(F &&f, Tuple &&t) {
        return apply_impl(std::forward<F>(f), std::forward<Tuple>(t),
                         
std::make_index_sequence<std::tuple_size<std::decay_t<Tuple>>::value>{});
    }

    template<class Closure, class Tuple>
    static void foreach_tuple(Closure &&closure, Tuple &&tuple) {
        //ns::
        apply([&](auto &&... args) {}, tuple);
    }
}


int main() {
    std::tuple t = {1,2,3};
    ns::foreach_tuple([](auto i){}, t);
    return 0;
}