c++boostshared-ptrsmart-pointersboost-smart-ptr

intrusive_ptr: Why isn't a common base class provided?

boost::intrusive_ptr requires intrusive_ptr_add_ref and intrusive_ptr_release to be defined. Why isn't a base class provided which will do this? There is an example here: http://lists.boost.org/Archives/boost/2004/06/66957.php, but the poster says "I don't necessarily think this is a good idea". Why not?

Update: I don't think the fact that this class could be misused with Multiple Inheritance is reason enough. Any class which derives from multiple base classes with their own reference count would have the same issue. Whether these refcounts are implemented via a base class or not makes no difference.

I don't think there's any issue with multithreading; boost::shared_ptr offers atomic reference counting and this class could too.

Solution

  • Boost provides a facility for that. It can be configured for either thread-safe or thread-unsafe refcounting:

    #include <boost/intrusive_ptr.hpp>
#include <boost/smart_ptr/intrusive_ref_counter.hpp>

class CMyClass
    : public boost::intrusive_ref_counter<
                               CMyClass,
                               boost::thread_unsafe_counter>
     ...

boost::intrusive_ptr<CMyClass> myPtr;

    http://www.boost.org/doc/libs/1_62_0/libs/smart_ptr/intrusive_ref_counter.html