Merge sorted ranges

Combines the elements in the sorted ranges [first1,last1) and [first2,last2), into a new range beginning at result with all its elements sorted.
The elements are compared using operator< for the first version, and comp for the second.

The elements in both ranges shall already be ordered according to this same criterion (operator< or comp). The resulting range is also sorted according to this.

　　template <class  InputIterator1, class InputIterator2, class OutputIterator>
    OutputIterator merge(InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, InputIterator2 last2, OutputIterator result) {
        while (true) {
            if (first1==last1) return std::copy(first2,last2,result);
            if (first2==last2) return std::copy(first1,last1,result);
            *result++ = (*first2<*first1)? *first2++ : *first1++;
        }
    }