Function patch

include/nlohmann/json.hpp:4226–4493

@brief applies a JSON patch @sa https://json.nlohmann.me/api/basic_json/patch/

    /// @brief applies a JSON patch
    /// @sa https://json.nlohmann.me/api/basic_json/patch/
    basic_json patch(const basic_json& json_patch) const
    {
        // make a working copy to apply the patch to
        basic_json result = *this;

        // the valid JSON Patch operations
        enum class patch_operations {add, remove, replace, move, copy, test, invalid};

        const auto get_op = [](const std::string & op)
        {
            if (op == "add")
            {
                return patch_operations::add;
            }
            if (op == "remove")
            {
                return patch_operations::remove;
            }
            if (op == "replace")
            {
                return patch_operations::replace;
            }
            if (op == "move")
            {
                return patch_operations::move;
            }
            if (op == "copy")
            {
                return patch_operations::copy;
            }
            if (op == "test")
            {
                return patch_operations::test;
            }

            return patch_operations::invalid;
        };

        // wrapper for "add" operation; add value at ptr
        const auto operation_add = [&result](json_pointer & ptr, basic_json val)
        {
            // adding to the root of the target document means replacing it
            if (ptr.empty())
            {
                result = val;
                return;
            }

            // make sure the top element of the pointer exists
            json_pointer top_pointer = ptr.top();
            if (top_pointer != ptr)
            {
                result.at(top_pointer);
            }

            // get reference to parent of JSON pointer ptr
            const auto last_path = ptr.back();
            ptr.pop_back();