/// combining them, this (as an optimization) directly combines the integers.
template <typename InputIteratorT>
hash_code hash_combine_range_impl(InputIteratorT first, InputIteratorT last) {
/// combining them, this (as an optimization) directly combines the integers.
template <typename InputIteratorT>
hash_code hash_combine_range_impl(InputIteratorT first, InputIteratorT last) {