Igor.Smirnov@cern.ch wrote:
May be I am behind progress, but I do not know a way to make cloning pointer (or that Mathias' value object, but this seems to be the same in principle) to be non-intrusive. You anyway need virtual cloning function in each class of the hierarchy.
Boost.Any, for example, copies dynamically objects without having to modify their type. Here is a simplistic possible implementation for our case. template<typename T, typename D> T* clone_function(const T& t) { return new D(static_cast<const D&>(t)); } template<typename T> class Container { template<typename D> Container(const D& d) : obj(new D(d)), clone(clone_function<T, D>) { } // copy constructor, operator=, etc. ~Container() { delete obj; } T* obj; T* (*clone)(const T&); }; As I said earlier, this has a few flaws: - one word per object is wasted. Polymorphic objects already have one word that identifies their type (the pointer to the vtable) - it assumes that the static type of the object the container acquires is the same as its dynamic type.