[boost] intrusive_ptr: proposal for common base class

From: Stefan Slapeta (stefan_nospam__at_[hidden])
Date: 2004-06-25 04:07:44

Hi all,

Sorry if this has been discussed yet, but I think there is an obvious 
pattern in the usage of intrusive_ptr which should be exposed as common 
functionality in boost.

In most of the cases you just want to handle a simple reference count 
and delete the object which is held by the intrusive_ptr when the 
reference count is decreased to zero. It's very annoying that you 
currently have to write external add_ref/release functions for every 
class you want to use with this smart pointer. Additionaly, it makes the 
code unreadable.

That's why I would like to suggest having a base class which provides 
the simplest functionality a user could expect from intrusive_ptr: 
handling the reference count and deleting the object. A class which 
should be maintained by intrusive_ptr can derive from it and would not 
have to provide any further interfaces.

I'm not glad about the class name 'intrusive_ptr_base' but I don't have 
any good ideas at the moment :(

Awaiting you comments! (code: see below)

Stefan

namespace boost {

class intrusive_ptr_base;

void intrusive_ptr_add_ref(intrusive_ptr_base*);
void intrusive_ptr_release(intrusive_ptr_base*);

class intrusive_ptr_base
{
        friend void intrusive_ptr_add_ref(intrusive_ptr_base*);
        friend void intrusive_ptr_release(intrusive_ptr_base*);

        int ref_count__;

protected:
        intrusive_ptr_base() : ref_count__(0) {}

        virtual ~intrusive_ptr_base() {}
};

inline void intrusive_ptr_add_ref(intrusive_ptr_base* o)
{
     ++o->ref_count__;
}

inline void intrusive_ptr_release(intrusive_ptr_base* o)
{
     if (--o->ref_count__ == 0) {
         delete o;
     }
}

} // namespace