[C++-sig] Re: reference counting pointers

[David Abrahams]

"Dusty Leary" <dleary at ttlc.net> writes:

>> 
>> Try 
>> 
>>     implicitly_convertible<intrusive_ptr<B>, intrusive_ptr<A> >();
>> 
>> Of course, if you just use shared_ptr instead, none of that is needed
>> ;-)
>> 
>
> why does it work automatically with shared_ptr and not with intrusive_ptr?

Because shared_ptr is special, and can do so safely.  The shared
pointer always manages the owning Python object, while intrusive_ptr
can't do that, and there's no guarantee that a derived-to-base
conversion on intrusive_ptr is safe (there might be no virtual
destructor in the base class).

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com