std::is_pod is deprecated in C++20

[Predelnik]

Newest msvc preview version already implements warning for this case. While it's not urgent in any way, it might be nice to replace it with either std::is_standard_layout or std::is_trivial to avoid warnings during compilation with newer standard support.

Here you can find more details on its deprecation:
https://stackoverflow.com/questions/48225673/why-is-stdis-pod-deprecated-in-c20

[nlohmann]

Thanks for reporting. std::is_pod is used here:

template < typename C = CharType,
           enable_if_t < std::is_signed<C>::value and std::is_unsigned<char>::value > * = nullptr >
static CharType to_char_type(std::uint8_t x) noexcept
{
    static_assert(sizeof(std::uint8_t) == sizeof(CharType), "size of CharType must be equal to std::uint8_t");
    static_assert(std::is_pod<CharType>::value, "CharType must be POD");
    CharType result;
    std::memcpy(&result, &x, sizeof(x));
    return result;
}

I think replacing this with std::is_standard_layout is suitable here, right?

[Predelnik]

To be able to do memcpy the requirement is std::is_trivially_copyable (stackoverflow link)

std::is_trivial also adds trivial default constructor requirement which might be useful here.

Standard layout however adds a lot of constraints I guess for most of them it's a bit strange to be unsatisfied in hypothetical CharType but I think since operations done are technically correct the rest can be blamed on user for passing something so unorthodox.

My conclusion is that std::is_trivial should be used. But I'm not an expert so it might be nice if someone would confirm my guess.

[nlohmann]

I created a branch for this: https://github.com/nlohmann/json/tree/feature/issue1913

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[dota17]

@Stale This issue should be pinned.

@nlohmann, hello.
Is there any new progress? It seems that this issue will be closed by bad bot.

[nlohmann]

I have a branch for this an will finish this after my vacation.