How to check size of ::testing::Types template?

Question

I'm creating a TYPED_TEST_SUITE and I want to get count of elements in ::testing::Types. The reason is to perform a static assertion, so I can be sure my tests are up to date with the source code.

With std::tuple following is possible:

int count = tuple_size<decltype(mytuple)>::value

Is there possibility to do the same with gtests's testing::Types? Or to convert std::tuple into testing::Types in a compile time?

Answer 1

Yes. You can do it this way:

template<typename...>
struct CountTypes;
template<typename... Args>
struct CountTypes<::testing::Types<Args...>> : std::integral_constant<int, sizeof...(Args)> {};

template<typename...>
struct ConvertTypes;
template<typename... Args>
struct ConvertTypes<::testing::Types<Args...>> { using type = std::tuple<Args...>;};

int main()
{
    using MyTypes = ::testing::Types<char, int>;
    static_assert(CountTypes<MyTypes>::value == 2);
    static_assert(std::is_same_v<ConvertTypes<MyTypes>::type, std::tuple<char, int>>);
    std::cout << CountTypes<MyTypes>::value << std::endl;
}