std::weak_ptr::operator=
From cppreference.com
                    
                                        
                    
                    
                                                            
                    |   weak_ptr& operator=( const weak_ptr& r ); 
 | 
(1) | (since C++11) | 
|   template< class Y >  
weak_ptr& operator=( const weak_ptr<Y>& r );  | 
(2) | (since C++11) | 
|   template< class Y >  
weak_ptr& operator=( const shared_ptr<Y>& r );  | 
(3) | (since C++11) | 
Replaces the managed object with the one managed by r. The object is shared with r. If r manages no object, *this manages no object too. Equivalent to weak_ptr<T>(r).swap(*this).
Contents | 
[edit] Parameters
| r | - | smart pointer to share an object with | 
[edit] Return value
*this
[edit] Exceptions
noexcept specification:  
noexcept
  [edit] Notes
The implementation may meet the requirements without creating a temporary weak_ptr object.