----Original Message---- From: Jonathan Wakely [mailto:cow@compsoc.man.ac.uk] Sent: 17 August 2005 14:17 To: boost@lists.boost.org Subject: Re: [boost] Propose adding Clone Smart Pointer (clone_ptr) to theboost library

Axter wrote:

...

It does not need a clone member if you apply strict pointer ownership logic, which is what a clone pointer normally does.

clone_ptr also needs the definitions of all derived classes to be visible, whereas something like ptr_container that uses a clone() member function only needs to see the definition of the base class and can do everything through the base class' interface.

I think it only needs the definition available for the constructor (which is where a class derived from his "copier" class is instantiated). [snip]

This would not be possible with std::vector<clone_ptr<Base> >:

// pc.h #include <boost/ptr_container/ptr_vector.hpp> struct Base { ~Base() {} virtual Base* clone() = 0; virtual void f() = 0; }; void fill(boost::ptr_vector<Base>&);

// pc.cc #include "pc.h" #include <boost/bind.hpp> #include <algorithm>

int main() { boost::ptr_vector<Base> v; fill(v); std::for_each(v.begin(), v.end(), boost::bind(&Base::f, _1)); return 0; }

The fill() function can now be implemented in another file and populate the vector with any type derived from Base, without recompiling pc.cc

I think that is supported with clone_ptr. The file implementing fill would need the full definition of the derived type(s) of course, but that is less restrictive. -- Martin Bonner Martin.Bonner@Pitechnology.com Pi Technology, Milton Hall, Ely Road, Milton, Cambridge, CB4 6WZ, ENGLAND Tel: +44 (0)1223 441434