C++11: Number of Variadic Template Function Parameters?
Just write this:
const std::size_t n = sizeof...(T); //you may use `constexpr` instead of `const`
Note that n
is a constant expression (i.e known at compile-time), which means you may use it where constant expression is needed, such as:
std::array<int, n> a; //array of n elements
std::array<int, 2*n> b; //array of (2*n) elements
auto middle = std::get<n/2>(tupleInstance);
Note that if you want to compute aggregated size of the packed types (as opposed to number of types in the pack), then you've to do something like this:
template<std::size_t ...>
struct add_all : std::integral_constant< std::size_t,0 > {};
template<std::size_t X, std::size_t ... Xs>
struct add_all<X,Xs...> :
std::integral_constant< std::size_t, X + add_all<Xs...>::value > {};
then do this:
constexpr auto size = add_all< sizeof(T)... >::value;
In C++17 (and later), computing the sum of size of the types is much simpler using fold expression:
constexpr auto size = (sizeof(T) + ...);
Hope that helps.