Кому интересно поломать голову

//где-то в классе
typedef std::set<ClassOne, ClassTwo> _Container;
 
// где-то в методе
return std::find(_Container::begin(), _Container::end(), predicate);

#include <iostream>
#include <deque>
 
template<typename T, class Container = std::deque<T, std::allocator<T>>>
class Stack
{
    using size_type = typename Container::size_type;
    using value_type = typename Container::value_type;
    using reference = typename Container::reference;
    using const_reference = typename Container::const_reference;
    
    Container m_container;
public:
    bool empty() const { return m_container.empty(); }
    size_type size() const { return m_container.size(); }
    value_type& top() { return m_container.back(); }
    const value_type& top() const { return m_container.back(); }
    void push(const value_type& val) { m_container.push_back(val); }
    void pop() { m_container.pop_back; }
};

template<typename T, class Container = std::deque<T, std::allocator<T>>>
class Stack : protected Container
{
public:
    using size_type = typename Container::size_type;
    using value_type = typename Container::value_type;
    using reference = typename Container::reference;
    using const_reference = typename Container::const_reference;
    
    using Container::empty;
    using Container::size;
    value_type& top() { return Container::back(); }
    const value_type& top() const { return Container::back(); }
    void push(const value_type& val) { Container::push_back(val); }
    void pop() { Container::pop_back; }
};