Method is_object

src/framework/io/json.cpp:215–217

        return *this;
    }
    kind_ = other.kind_;
    bool_value_ = other.bool_value_;
    number_value_ = other.number_value_;
    string_value_ = other.string_value_;
    array_value_ = other.array_value_ ? std::make_unique<Array>(*other.array_value_) : nullptr;
    object_value_ = other.object_value_ ? std::make_unique<Object>(*other.object_value_) : nullptr;