class Context
{
public:
    template<typename Property>
    void Put(typename Property::value_type& val)
    {
        m_map[typeid(Property)] = std::static_pointer_cast<void>(val);
    }

    template<typename Property>
    typename Property::value_type Get() const
    {
        typedef Property::value_type result_type;
        auto it = m_map.find(typeid(Property));
        if (it == m_map.end())
            return result_type();
        return std::static_pointer_cast<typename result_type::element_type>(it->second);
    }
private:
    std::map<std::type_index, std::shared_ptr<void>> m_map;
};

struct first_bone
{
    typedef BonePtr value_type;
};

void example()
{
    Context ctx;
    BonePtr b;
    ctx.Put<first_bone>(b);
    BonePtr bb = ctx.Get<first_bone>();
}