std::char_traits<std::byte> removed in libc++ 18

[Altren]

Reflect-cpp can't be compiled with XCode 16.3 because of this.
https://github.com/llvm/llvm-project/blob/release/17.x/libcxx/docs/ReleaseNotes/17.rst#llvm-18
So it seems that something like std::vectorstd::byte should be used.
I tried to do this myself, and few build issues in the library are trivial, but I don't understand what's wrong here:

In file included from /Users/gevmenov/libs/reflect-cpp/include/rfl.hpp:55:
In file included from /Users/gevmenov/libs/reflect-cpp/include/rfl/enums.hpp:7:
/Users/gevmenov/libs/reflect-cpp/include/rfl/internal/enums/StringConverter.hpp:42:19: error: static assertion failed due to requirement 'names_.size != 0': No enum could be identified. Please choose enum values between 0 to 127 or for flag enums choose 1,2,4,8,16,...
   42 |     static_assert(names_.size != 0,
      |                   ^~~~~~~~~~~~~~~~
/Users/gevmenov/libs/reflect-cpp/include/rfl/generic/../parsing/Parser_default.hpp:83:32: note: in instantiation of member function 'rfl::internal::enums::StringConverter<std::byte>::string_to_enum' requested here
   83 |               StringConverter::string_to_enum);
      |                                ^
/Users/gevmenov/libs/reflect-cpp/include/rfl/generic/../parsing/VectorReader.hpp:28:70: note: in instantiation of member function 'rfl::parsing::Parser<rfl::msgpack::Reader, rfl::msgpack::Writer, std::byte, rfl::Processors<>>::read' requested here
   28 |         return Parser<R, W, std::remove_cvref_t<T>, ProcessorsType>::read(*r_,
      |                                                                      ^
/Users/gevmenov/libs/reflect-cpp/include/rfl/msgpack/Reader.hpp:87:38: note: in instantiation of member function 'rfl::parsing::VectorReader<rfl::msgpack::Reader, rfl::msgpack::Writer, std::vector<std::byte>, rfl::Processors<>>::read' requested here
   87 |       const auto err = _array_reader.read(_arr.ptr[i]);
      |                                      ^
/Users/gevmenov/libs/reflect-cpp/include/rfl/generic/../parsing/VectorParser.hpp:58:29: note: in instantiation of function template specialization 'rfl::msgpack::Reader::read_array<rfl::parsing::VectorReader<rfl::msgpack::Reader, rfl::msgpack::Writer, std::vector<std::byte>, rfl::Processors<>>>' requested here
   58 |         const auto err = _r.read_array(vector_reader, _arr);
      |                             ^
/Users/gevmenov/libs/reflect-cpp/include/rfl/generic/../parsing/ViewReader.hpp:53:51: note: in instantiation of member function 'rfl::parsing::VectorParser<rfl::msgpack::Reader, rfl::msgpack::Writer, std::vector<std::byte>, rfl::Processors<>>::read' requested here
   53 |       auto res = Parser<R, W, T, ProcessorsType>::read(_r, _var);
      |                                                   ^
/Users/gevmenov/libs/reflect-cpp/include/rfl/generic/../parsing/ViewReader.hpp:102:6: note: in instantiation of function template specialization 'rfl::parsing::ViewReader<rfl::msgpack::Reader, rfl::msgpack::Writer, rfl::NamedTuple<rfl::Field<internal::StringLiteral<11>{{"bytestring"}}, std::vector<std::byte> *>>, rfl::Processors<>>::assign_if_field_matches<0, msgpack_object, rfl::NamedTuple<rfl::Field<internal::StringLiteral<11>{{"bytestring"}}, std::vector<std::byte> *>>, std::vector<rfl::Error>, std::array<bool, 1>, std::array<bool, 1>>' requested here
  102 |     (assign_if_field_matches<is>(_r, _current_name, _var, _view, _errors,
      |      ^
/Users/gevmenov/libs/reflect-cpp/include/rfl/generic/../parsing/ViewReader.hpp:33:5: note: in instantiation of function template specialization 'rfl::parsing::ViewReader<rfl::msgpack::Reader, rfl::msgpack::Writer, rfl::NamedTuple<rfl::Field<internal::StringLiteral<11>{{"bytestring"}}, std::vector<std::byte> *>>, rfl::Processors<>>::assign_to_matching_field<0, msgpack_object, rfl::NamedTuple<rfl::Field<internal::StringLiteral<11>{{"bytestring"}}, std::vector<std::byte> *>>, std::vector<rfl::Error>, std::array<bool, 1>, std::array<bool, 1>>' requested here
   33 |     assign_to_matching_field(*r_, _name, _var, view_, errors_, found_, set_,
      |     ^
/Users/gevmenov/libs/reflect-cpp/include/rfl/msgpack/Reader.hpp:106:22: note: in instantiation of member function 'rfl::parsing::ViewReader<rfl::msgpack::Reader, rfl::msgpack::Writer, rfl::NamedTuple<rfl::Field<internal::StringLiteral<11>{{"bytestring"}}, std::vector<std::byte> *>>, rfl::Processors<>>::read' requested here
  106 |       _object_reader.read(name, val);
      |                      ^
/Users/gevmenov/libs/reflect-cpp/include/rfl/generic/../parsing/NamedTupleParser.hpp:308:16: note: in instantiation of function template specialization 'rfl::msgpack::Reader::read_object<rfl::parsing::ViewReader<rfl::msgpack::Reader, rfl::msgpack::Writer, rfl::NamedTuple<rfl::Field<internal::StringLiteral<11>{{"bytestring"}}, std::vector<std::byte> *>>, rfl::Processors<>>>' requested here
  308 |       err = _r.read_object(reader, _obj_or_arr);
      |                ^
/Users/gevmenov/libs/reflect-cpp/include/rfl/generic/../parsing/NamedTupleParser.hpp:121:14: note: in instantiation of member function 'rfl::parsing::NamedTupleParser<rfl::msgpack::Reader, rfl::msgpack::Writer, false, true, false, rfl::Processors<>, rfl::Field<internal::StringLiteral<11>{{"bytestring"}}, std::vector<std::byte> *>>::read_object_or_array' requested here
  121 |       return read_object_or_array(_r, *obj, _view);
      |              ^
/Users/gevmenov/libs/reflect-cpp/include/rfl/generic/../parsing/Parser_default.hpp:262:49: note: in instantiation of member function 'rfl::parsing::NamedTupleParser<rfl::msgpack::Reader, rfl::msgpack::Writer, false, true, false, rfl::Processors<>, rfl::Field<internal::StringLiteral<11>{{"bytestring"}}, std::vector<std::byte> *>>::read_view' requested here
  262 |         Parser<R, W, ViewType, ProcessorsType>::read_view(_r, _var, &view);
      |                                                 ^
/Users/gevmenov/libs/reflect-cpp/include/rfl/generic/../parsing/Parser_default.hpp:74:18: note: in instantiation of member function 'rfl::parsing::Parser<rfl::msgpack::Reader, rfl::msgpack::Writer, test_bytestring::TestStruct, rfl::Processors<>>::read_struct' requested here
   74 |           return read_struct(_r, _var);
      |                  ^
/Users/gevmenov/libs/reflect-cpp/include/rfl/msgpack/read.hpp:24:40: note: in instantiation of member function 'rfl::parsing::Parser<rfl::msgpack::Reader, rfl::msgpack::Writer, test_bytestring::TestStruct, rfl::Processors<>>::read' requested here
   24 |   return Parser<T, Processors<Ps...>>::read(r, _obj);
      |                                        ^
/Users/gevmenov/libs/reflect-cpp/include/rfl/msgpack/read.hpp:43:10: note: in instantiation of function template specialization 'rfl::msgpack::read<test_bytestring::TestStruct>' requested here
   43 |   return read<T, Ps...>(_bytes.data(), _bytes.size());
      |          ^
/Users/gevmenov/libs/reflect-cpp/tests/msgpack/test_bytestring.cpp:19:3: note: in instantiation of function template specialization 'write_and_read<test_bytestring::TestStruct>' requested here
   19 |   write_and_read(test);
      |   ^
/Users/gevmenov/libs/reflect-cpp/include/rfl/internal/enums/StringConverter.hpp:42:31: note: expression evaluates to '0 != 0'
   42 |     static_assert(names_.size != 0,
      |                   ~~~~~~~~~~~~^~~~```

[Altren]

May be this issue is not related to the Bytestring. I'd better wait for XCode 16.3 release before getting deeper into this.

Also std::char_traits<std::byte> was removed by mistake (it should've been only marked as deprecated), and was reintroduced into llvm with this fix llvm/llvm-project@cce062d but apparently, XCode developers missed that fix.

[YBerd]

Just in case: this issue is not related to Xcode itself, it is about LLVM (clang / libc++) 19.x that xcode 16.3 is based onto.

LLVM docs

The base template for std::char_traits has been removed in LLVM 19. If you are using std::char_traits with types other than char, wchar_t, char8_t, char16_t, char32_t or a custom character type for which you specialized std::char_traits, your code will stop working. The Standard does not mandate that a base template is provided, and such a base template is bound to be incorrect for some types, which could currently cause unexpected behavior while going undetected

[Altren]

Fixed here: #369