Re: Making a smart pointer which works with incomplete types

Most shared_ptr implementations will use ECBO for the deleter. i.e.
template<class T,class D>
struct shared_ptr_imp:D{
T* data;
unsigned refcount;
void decrementReferenceCount()
    {
        if(data)
        {
            // decrement reference count and then:
            if(<refcount == 0>)
            {
                this->D::operator()(data);//exapanded to see whats
really happening
            }
        }
    }
};
In the vast majority of cases, D is something like
template<class T>
struct DeleteMe{
   void operator()(T* d){delete d;}
};//DeleteMe has no data, therefore ECBO add no storage
Using ECBO, you will find this
sizeof(shared_ptr_imp<T,DeleteMe>)==(sizeof(T*)+sizeof(unsigned));//
ignoring padding etc

Only in the rare cases where the deleter actually has data you would
see an increase in size, i.e.
template<class T,class U>
struct Alias{//keep shared_ptr<U> alive as long as shared_ptr<T>
exists
   void operator()(T* d){}
   Alias(shared_ptr<U> const&k):m_keep(k){}
private:
   shared_ptr<U> m_keep;
};//shared_ptr alias that preserves the ordering invaraints

Lance