std::initializer_list<T>::size
Min standard notice:
Obtains the number of elements in the initializer list.
# Declarations
size_type size() const noexcept;
(since C++11) (constexpr since C++14)
# Return value
std::distance(begin(), end())
# Example
#include <initializer_list>
static_assert(std::initializer_list{1, 2, 3}.size() == 3);
int main() {}