Correct way to initialize a container of std::byte

Question

What is the correct way of initializing a container with predetermined std::byte values?

std::array<std::byte, 2> arr{0x36, 0xd0} for array results in

Enum std::byte has not constant to represent the integer value of X

and compiler errors. Vector and initializer lists are a no-go too.

Is std::vector with std::copy and casts really the intended way of handling this?

Answer 1

You will have to write std::byte{0x36}, because there is no implicit conversion from an int to a enum class.

std::array<std::byte, 2> arr = {std::byte{0x36}, std::byte{0xd0}};

If you don't want to write std::byte every single time, write a helper function:

template<typename... Ts>
std::array<std::byte, sizeof...(Ts)> make_bytes(Ts&&... args) noexcept {
    return{std::byte(std::forward<Ts>(args))...};
}

auto arr = make_bytes(0x36, 0xd0);

Answer 2

With C++20, you can utilize to_array to create an array of unsigned char easily, then bit_cast it to an array of byte:

auto arr = std::bit_cast<std::array<std::byte, 2>>(
    std::to_array<unsigned char>({0x36, 0xd0, /*...*/})
);