packet_reader

Reads structured data from a packet, with proper error handling:

void read_foo(Packet *packet) {
    struct { int x = {}, y = {}; float z = {}; } foo = {};
    // read `foo`'s fields from `packet`, handle errors
}

The implementation uses variadic templates and a simple data format/protocol. Error handling uses simple bools, but could be substituted with more sophisticated approaches (the implementation of the public get function would be slightly more complex).

An invalid read is caught by the conditional based on read<Type> and the buffer index is left unchanged. The failure is communicated to the Packet::get caller. An attempt to get an unsupported type is caught at compile-time and generates a suitable error message based on the unsatisfied constraints:

error: no matching function for call to ‘codex::Packet::get<double>(std::nullptr_t)’
     packet.get<double>(nullptr);
                               ^
note: candidate: ‘auto codex::Packet::get(auto:43* ...) [with auto:43 = {double}]’
   44 |     auto get(Readable auto *...ps) { return (this->read(ps) && ...); }
      |          ^~~
note: constraints not satisfied
In instantiation of ‘auto codex::Packet::get(auto:43* ...) [with auto:43 = {double}]’:
  required by the constraints of ‘template<class ... auto:43>  requires (... && Readable<auto:43>) auto codex::Packet::get(auto:43* ...)’
note: the expression ‘(... && Readable<auto:43>) [with auto:43 = {double}]’ evaluated to ‘false’