[FGL utility] make_byte_array

#pragma once
#ifndef FGL_MAKE_BYTE_ARRAY_HPP_INCLUDED
#define FGL_MAKE_BYTE_ARRAY_HPP_INCLUDED

#include <cstddef> // size_t, byte
#include <utility> // index_sequence, make_index_sequence
#include <array>
#include <type_traits>
#include <concepts>

namespace fgl {

template <class T>
concept StdArrayOfBytes = requires
{
    requires std::same_as<
        std::byte,
        std::remove_cv_t<typename T::value_type>>;

    requires std::same_as<
        std::array<typename T::value_type, sizeof(T)>,
        std::remove_cv_t<T>>;
};

template <class T>
concept StdArrayOfConstBytes = requires
{
    requires StdArrayOfBytes<T>;
    requires std::is_const_v<typename T::value_type>;
};

/// returns a std::array<std::byte> from cstring literal. removes null term.
template<std::size_t LEN> [[nodiscard]]
constexpr std::array<const std::byte, LEN-1> make_byte_array(
    const char (&cstr)[LEN])
{
    return
        [&]<std::size_t ... I>(std::index_sequence<I...>)
        constexpr -> std::array<const std::byte, LEN-1>
        {
            return {{static_cast<const std::byte>(cstr[I])...}};
        }(std::make_index_sequence<LEN-1>());
}

} // namespace fgl

#endif // FGL_MAKE_BYTE_ARRAY_HPP_INCLUDED