[Bug c++/122828] [Reflection] Enum to string from P2996R13 does not compile

[redi at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122828

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2025-11-25
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
The example is:

#include <print>
#include <meta>

template<typename E, bool Enumerable = std::meta::is_enumerable_type(^^E)>
  requires std::is_enum_v<E>
constexpr std::string_view enum_to_string(E value) {
  if constexpr (Enumerable)
    template for (constexpr auto e :
                  std::define_static_array(std::meta::enumerators_of(^^E)))
      if (value == [:e:])
        return std::meta::identifier_of(e);

  return "<unnamed>";
}

int main() {
  enum Color : int;
  static_assert(enum_to_string(Color(0)) == "<unnamed>");
  std::println("Color 0: {}", enum_to_string(Color(0)));  // prints '<unnamed>'

  enum Color : int { red, green, blue };
  static_assert(enum_to_string(Color::red) == "red");
  static_assert(enum_to_string(Color(42)) == "<unnamed>");
  std::println("Color 0: {}", enum_to_string(Color(0)));  // prints 'red'
}