On Mon, Jun 29, 2009 at 11:36 AM, Ross Levine <ross.levine@uky.edu> wrote:
On Sun, Jun 28, 2009 at 5:10 PM, Christian Schladetsch < christian.schladetsch@gmail.com> wrote:
One initial issue that may break any interest is that instances put into the container must be of a type T that derives from heterogenous::base<T>.
So, how is this different from using a ptr_container and dynamic_cast?
The instances in a heterogenous::container are added to the container using the correct allocator, and are duplicated using the correct (and same) allocator. struct base {}; struct derived : base {}; typedef ptr_vector<base, heap_clone_alocator, custom_allocator<base> > vec; vec v0; v0.push_back(new T(args)); // doesnt use the correct allocator vec v1 = v0; // clones are not created using the containers allocator as opposed to: typedef heterogenous::vector<custom_allocator> vec; vec v0; v0.push_back<T>(args); // uses correct allocator vec v1 = v0; // clones created using correct allocator, no custom clone_allocator required Of course, I have missed here that for this to work, T must derive from base<T>. There is a good case to be made for using std::vector<any> to do a similar thing. It's much simpler for a start. However, boost::any uses the heap and doesn't know about or use allocators. I've made modifications to boost::any, giving it an allocator type. See http://tinyurl.com/mxh9gm. This allows, for instance: typedef any<custom_allocator<char> > any_type; typedef std::vector<any_type, custom_allocator<any_type> > vec; vec v; v.push_back(T0(42)); v.push_back(T1("foo")); vec v2 = v; And this works - and T0 and T1 don't have to derive from anything. However, it creates the instances to add on the stack, then copies them into the container. v.push_back<type>(..args..) doesn't make a copy - it is constructed in-place using the correct storage provided by the allocator. This may be a pretty weak argument against a 'heterogenous container' based on any rather than ptr_container. Perhaps just making any<> take an allocator type argument would suffice for this? Regards, Christian.