How to implement equal range "iterator"

Question

how would one implement generic (aka works for multimap, sorted vector ...) equal range iterator? By this I mean it is an iterator that is a pair of iterators (begin and end of a particular equal_range)

Motivation for this is that I have a multimap that is called sortedword2word , and I use it to detect anagrams in an array of strings. So I would like to have a way to iterate over each equal range easily (easily as in LOC/readability way - I know I can easily do it by manually checking for .end() and if next is the same as current...)

If boost has implemented functionality like this that is acceptable A also.

Answer 1

Maybe like this:

template <typename Iter> class eqrange
{
    Iter a, b, e;

    void adv()
    {
        e = a;
        while (e != b && *e == *a) { ++e; }
    }

public:

    eqrange(Iter x, y) : a(x), b(y) { adv(); }

    Iter begin() { return a; }
    Iter end()  { return e; }

    eqrange & operator++() { b = e; adv(); }

    bool operator==(eqrange const & rhs) const
    {
        return a == rhs.a && b == rhs.b && e == rhs.e;
    }

    eqrange make_end() const
    { 
        return eqrange(b, b);
    }
};

template <typename Iter>
eqrange<Iter> er(Iter b, Iter e)
{
    return eqrange<Iter>(b, e);
}

Usage:

auto r = er(v.begin(), v.end()), e = r.make_end();

while (r != e)
{
    for (auto x : r) { /* ... */ }
    ++r;
}