Schoenborn, Oliver wrote:[snip]
OTOH,
... 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.
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.
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