I've improved https://stackoverflow.com/a/60271100/12894563 answer. 'If constexpr' can help in this situation:
template <typename T>struct always_false : std::false_type {};template <typename T>bool isFunction(const T& aVariable){ if constexpr(std::is_same_v<T, int> || std::is_same_v<T, anEnum>) { std::cout << "int\n"; // put your code here return true; } else { static_assert(always_false<T>::value, "You should declare non-template function or write if constexpr branch for your type"); return false; }}bool isFunction(std::string_view){ std::cout << "std::string_view\n"; return true;}int main(){ isFunction(std::string_view("1L")); isFunction(1); //isFunction(1L); // will produce an error message from static_assert}isFunction(1L) will fail becuase there is no overloaded function or 'if constexpr' branch.
UPDATE:Fixed missed
template <typename T>struct always_false : std::false_type {};