OpenAssetTools/src/ObjCommon/Json/JsonOptional.h

#pragma once

#include <nlohmann/json.hpp>
#include <optional>

// partial specialization (full specialization works too)
namespace nlohmann
{
    template<typename T> struct adl_serializer<std::optional<T>>
    {
        static void to_json(json& j, const std::optional<T>& opt)
        {
            if (!opt.has_value())
            {
                j = nullptr;
            }
            else
            {
                j = *opt; // this will call adl_serializer<T>::to_json which will
                          // find the free function to_json in T's namespace!
            }
        }

        static void from_json(const json& j, std::optional<T>& opt)
        {
            if (j.is_null())
            {
                opt = std::nullopt;
            }
            else
            {
                opt = j.template get<T>(); // same as above, but with
                                           // adl_serializer<T>::from_json
            }
        }
    };
} // namespace nlohmann