STL源码剖析之算法：partial_sum

template <class Iterator>
typename iterator_traits<Iterator>::value_type*
value_type(Iterator &iterator) {
    return static_cast<typename iterator_traits<Iterator>::value_type*>(0);
}

template <class InputIterator, class OutputIterator, class T, class BinaryOperation>
OutputIterator __partial_sum(InputIterator first, InputIterator last,
                             OutputIterator result, T*, BinaryOperation binary_op) {
    T value = *first;
    while(++first != last) {
        value = binary_op(value, *first);
        *++result = value;
    }
    return ++result;
}

template <class InputIterator, class OutputIterator, class BinaryOperation>
OutputIterator partial_sum(InputIterator first, InputIterator last,
                           OutputIterator result, BinaryOperation binary_op) {
    if(first == last) return result;
    *result = *first;
    return __partial_sum(first, last, result, value_type(first), binary_op);
}