This implements constexpr assign, find, compare and length functions proposed in p0426r1.
Synopsis:
static constexpr void assign(char_type& c1, const char_type& c2) noexcept; static constexpr int compare(const char_type* s1, const char_type* s2, size_t n); static constexpr size_t length(const char_type* s); static constexpr const char_type* find(const char_type* s, size_t n, const char_type& a);
Note that only primary template char_traits<T> and char_traits<char> specialization are addressed for now...
What about GCC? Surely it implements some if not most of these.