Jaap Suter wrote:
1. Instead of providing the two options of deriving and embedding, let the user provide ADL-style 'next' and 'prev' lookup functions that for a given type provide hooks to the intrusive containers. Look at the boost::intrusive_ptr documentation for more information on this style. You can still provide the existing two methods as possible ways of providing these hooks, but if my legacy code (or for some other reason) has types with their own next and prev pointers, I still want to be able to use your code.
I'm not sure about this, most of the difficulty is involved in manipulating the links - iterator adaptor or facade can be used to easily create iterators for types with their own next and prev pointers.
2. As you mention, inserting an object twice leads to problems. In general, intrusive lists need to be handled with more care. I would like to see a diagnostics mode that checks invariants and preconditions. Things to check for would be checking if an instance doesn't already exist on inserts, and checking whether there are no loops in a list. Because this will make list-manipulation really slow, I'd like to be able to enable this on a per-instance basis, probably through boolean-ish or policy-based template parameters.
If there was a check that a node wasn't in a container on insertion wouldn't these problems disappear? Daniel