Re: Multimap: how to get a key list?

Alternatively, we could shoe-horn an STL algorithm. For example (and
assuming we want each instance of duplicate keys:

    template <class Inserter>
    struct Assign_First : public Inserter
    {
        typedef typename Inserter::container_type container_type;

        Assign_First(container_type& c) : Inserter(c) { }

        Assign_First& operator*() { return *this; }

        template <typename Pair>
        Assign_First& operator=(const Pair& value)
        {
            Inserter::operator=(value.first);
            return *this;
        }
    };

    ...

    typedef std::multimap<int, std::string> MM;
    MM mm;

    typedef std::vector<MM::key_type> Keys;
    Keys keys;

    std::copy(mm.begin(), mm.end(),
              Assign_First<std::back_insert_iterator<Keys> >(keys));