Re: [Boost-users] shared_ptr<> null deleter

From: David Walthall (walthall_at_[hidden])
Date: 2008-05-16 16:16:30

Sohail Somani wrote:
> I was recently torn between doing this or thinking whether I'm doing it 
> wrong. I'm still not sure whether using shared pointers everywhere with 
> null deleters for stack allocated objects is The Right Thing. It kind of 
> defeats the purpose of shared_ptr which is to ensure that the lifetime 
> of the pointer is guaranteed for you. With null deleters, maintenance 
> programmers may do the wrong thing (stuff something in an event queue 
> deep down, for example.)
> 
> If anyone has any opinion (for or against) please shout!

I would say that this is a bad idea.  It seems like there is an implicit 
contract when using shared_ptrs that the object won't be destroyed as 
long as anyone has a copy of that shared_ptr.  (One way to advertise 
that copies of the smart pointer might not preserve the object could be 
to pass a weak_ptr instead of a shared_ptr.  Unfortunately, the lock 
method of the weak_ptr could still cause problems because it returns a 
shared_ptr, and you could still end up with a stale pointer.)

Overall, it seems like using a shared_ptr for stack objects is 
misleading, and as a result, may eventually lead to difficult to trace 
bugs.  Unless allocating and deallocating the object is a bottleneck in 
your code, the potential costs outweigh the benefits.

David