Re: [boost] Re: Single ownership w/weak_ptrs? (was Cyclic smart pointers)

From: Larry Evans (jcampbell3_at_[hidden])
Date: 2003-06-01 22:00:14

Chuck Messenger wrote:
> Schoenborn, Oliver wrote:
[snip]
>>
>> ... Strict ownership means that only one object at any
>> given time can be the owner. This is pretty straightforward and the raw
>> pointer example shows that there is no such thing as cyclic strict 
>> ownership
>> that works, at least within the above definition of ownership, 
> 
> 
> Which is why the strict ownership paradigm doesn't work with cyclic 
> structures.  Inherently, in the general case, cyclic structures 
> *require* garbage collection (or to be more precise, some dynammic 
> programming cycle-finding algorithm, whether or not you call it "garbage 
> collection") to harvest stranded cycles of objects.
> 
> Yes, as Peter Dimov suggested, you can sort of "game" the problem by 
> dividing your structures into Vertex and Edge types, allowing for a 
> classic strict ownership hierarchy.  But that just leaves the garbage 
> collection problem to the programmer.
OTOH,

http://groups.google.com/groups?dq=&hl=en&lr=&ie=UTF-8&oe=UTF-8&threadm=dilpugnc13c.fsf%40isolde.research.att.com&rnum=1&prev=/groups%3Fdq%3D%26hl%3Den%26lr%3D%26ie%3DUTF-8%26oe%3DUTF-8%26selm%3Ddilpugnc13c.fsf%2540isolde.research.att.com

seems to support Oliver's viewpoint.  I remember reading another post
somewhere where someone required cycles because he was
creating a graph from reading input from a file and couldn't know who
owned who.  However, if he's reading from a file, he must
have some map from vertex_name -> vertex_node, and this map
would be the sole owner.  All the vertex_nodes would simply be
weak_ptr's to other vertex_nodes.

The above cited post was in a long thread discussing on this topic.
It might be worth reading.