Re: [Boost-users] [ptr_container] How to transfer ownership from smart_ptr to ptr_container

From: Thorsten Ottosen (thorsten.ottosen_at_[hidden])
Date: 2007-06-22 11:04:54

Peter Dimov skrev:
> Thorsten Ottosen wrote:
>> Seweryn Habdank-Wojewódzki skrev:
>>> Hi!
>>>
>>> Is there any smart_ptr and ptr_container that can transfer ownership
>>> of pointer, to avoid useless copy-construction and destruction of
>>> the object.
>> I guess you can't release a shared_ptr, even though it's use count is
>> 1.
>> Peter, any reason for not having a release() given that its
>> precondition is unique() is true?
> 
> The precondition is subject to race conditions with weak_ptr::lock. Even if 
> you get back a T* from shared_ptr<T>::release, you won't necessarily be able 
> to destroy it properly since you have no idea where it points. It could be a 
> pointer to a static object, a pointer to a base class without a virtual 
> destructor, a pointer to a member of type T. If you want release(), 
> shared_ptr is not the right tool. auto_ptr or unique_ptr offer release().

ok.

> The problem today (in a pre-rvalue ref world) is that (a) we have no 
> unique_ptr and (b) even if we had, vector< unique_ptr > still wouldn't work. 
> I'd have expected ptr_vector<T> to be essentially an alias for vector< 
> unique_ptr<T> > since there's obviously a need for that, but apparently it 
> doesn't quite work that way. 

No, there are quite a few differences, although both allows you to move 
a pointer from the collection. Anyway, I understood our users problem as 
one needing a shared_ptr. If he can use std::auto_ptr, there is no 
problem AFAICT.

-Thorsten