std::set和std::multiset

std::set

template <typename Tp>
struct Identity_
{
    const Tp& operator()(const Tp& x) const { return x; }
};
template <typename Key, typename Compare = std::less<Key>>
class Myset 
{
public:
    typedef Key     key_type;
    typedef Key     value_type;
    typedef Compare key_compare;
    typedef Compare value_compare;
private:
    typedef Rb_tree<key_type, value_type, Identity_<value_type>, key_compare> Rep_type;
    Rep_type m_rbtree;  // red-black tree representing set
public:
    typedef typename Rep_type::iterator iterator;
    typedef typename Rep_type::size_type size_type;
    Myset() : m_rbtree() {}
    Myset(Myset&& x) : m_rbtree(std::move(x.m_rbtree)) {}

    iterator begin() const { return m_rbtree.begin(); }
    iterator end() const { return m_rbtree.end(); }
    bool empty() const { return m_rbtree.empty(); }
    size_type size() const { return m_rbtree.size(); }
    void swap(Myset& x) { m_rbtree.swap(x.m_rbtree); }

    std::pair<iterator, bool> insert(const value_type& x)
    {
        return m_rbtree.insert_unique(x);
    }
    void erase(iterator position) 
    {
        m_rbtree.erase(position);
    }
    size_type erase(const key_type& x) 
    {
        return m_rbtree.erase(x);
    }
    void clear() { m_rbtree.clear(); }

    iterator find(const key_type& x) { return m_rbtree.find(x); }
    size_type count(const key_type& x) const 
    {
        return m_rbtree.count(x);
    }
};

std::multiset

template <typename Key, typename Compare = std::less<Key>>
class Mymultiset
{
public:
    typedef Key     key_type;
    typedef Key     value_type;
    typedef Compare key_compare;
    typedef Compare value_compare;
private:
    typedef Rb_tree<key_type, value_type, Identity_<value_type>, key_compare> Rep_type;
    Rep_type m_rbtree;  
public:
    typedef typename Rep_type::iterator iterator;
    typedef typename Rep_type::size_type size_type;
    Mymultiset() : m_rbtree() {}
    Mymultiset(Mymultiset&& x) : m_rbtree(std::move(x.m_rbtree)) {}

    iterator begin() const { return m_rbtree.begin(); }
    iterator end() const { return m_rbtree.end(); }
    bool empty() const { return m_rbtree.empty(); }
    size_type size() const { return m_rbtree.size(); }
    void swap(Mymultiset& x) { m_rbtree.swap(x.m_rbtree); }

    iterator insert(const value_type& x)
    {
        return m_rbtree.insert_equal(x);
    }
    void erase(iterator position)
    {
        m_rbtree.erase(position);
    }
    size_type erase(const key_type& x)
    {
        return m_rbtree.erase(x);
    }
    void clear() { m_rbtree.clear(); }

    iterator find(const key_type& x) { return m_rbtree.find(x); }
    size_type count(const key_type& x) const
    {
        return m_rbtree.count(x);
    }
};