Function get_ptr

lesson6-Segmentation/json.hpp:19567–19571

    template<typename PointerType, typename std::enable_if<
                 std::is_pointer<PointerType>::value, int>::type = 0>
    auto get_ptr() noexcept -> decltype(std::declval<basic_json_t&>().get_impl_ptr(std::declval<PointerType>()))
    {
        // delegate the call to get_impl_ptr<>()
        return get_impl_ptr(static_cast<PointerType>(nullptr));
    }

    /*!
    @brief get a pointer value (implicit)