Automatically convert on-disk mixed endian types to native

endian_struct.hpp

#include <algorithm>
#include <bit>
#include <cstddef>
#include <type_traits>

template <typename T, std::endian endianess,
          typename = std::enable_if_t<std::is_scalar_v<T>>>
class endian {
 public:
  constexpr endian() noexcept = default;

  endian(const T &val) noexcept : _val{swap(val)} {}

  operator T() const noexcept { return swap(_val); }

 private:
  static T swap(T val) noexcept {
    if constexpr (endianess == std::endian::native) {
      return val;
    }

    using bytes_type = std::byte[sizeof(T)];
    static_assert(sizeof(bytes_type) == sizeof(T));

    auto &bytes = reinterpret_cast<bytes_type &>(val);
    std::reverse(std::begin(bytes), std::end(bytes));
    return val;
  }

  T _val{};
};

template <typename T>
using big_endian = endian<T, std::endian::big>;

template <typename T>
using little_endian = endian<T, std::endian::little>;