Re: [boost] Abstract STL Container Adaptors

I really cannot follow this.

If the container is type erased, how do you get that information you are alluding to back out?

Here's a very rough sketch demonstrating just one member (set::count). Many details are ignored, obviously. template<typename ValueType> struct abstract_set { typedef ValueType key_type; typedef ValueType value_type; typedef std::size_t size_type; // etc. template<typename GenericSet> abstract_set(GenericSet const & set) : m_holder(new holder<GenericSet>(set)) {} size_type count(value_type const & value) const { return m_holder->count(value); } private: struct holder_base { virtual size_t count(value_type const &) const = 0; }; template<typename GenericSet> struct holder : holder_base { holder(GenericSet const & set) : m_container(set) {} virtual size_t count(value_type const & value) const { return m_container.count(value); } private: GenericSet const & m_container; }; boost::shared_ptr m_holder; }; void my_algorithm(abstract_set<int> const & set) { std::cout << "7 in set? " << bool(set.count(7)) << std::endl; } int main() { std::set<int> set0; set0.insert(4); my_algorithm(set0); std::tr1::unordered_set<int> set1; set1.insert(7); my_algorithm(set1); return 0; }

There are plenty of papers and implementations of any_iterator out there. Why is that not sufficient for your needs?

I want the container, not just an iterator. I might want to test for membership or add elements to the container.