https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115098
--- Comment #1 from 康桓瑋 <hewillk at gmail dot com> --- std::bitset has similar issues: #include <bitset> std::bitset<1> bitset; typename std::bitset<1>::reference bit_ref(bitset, 0); // well-formed in libstdc++ https://godbolt.org/z/T4qvv8TcG