Nef_3: Proof of concept for no-hashmap approach.

[GilesBathgate]

Summary of Changes

In Nef_3 hashmaps are used to associate information with objects at runtime, for example, to flag that a HalfEdge has been visited there might be a Unique_hash_map<Halfedge_handle,bool> visited;. If the class HalfEdge had a member variable called visited this could be used instead to indicate whether the edge had been visited (although it would have to be reset afterwards) However this would mean adding lots of extraneous data to the classes depending on the method or algorithm that is processing the list of objects.

There is a generalised info container on all the classes which could be used. However, a mechanism is needed to make sure that the existing info isn't overwritten, and is restored to whatever it was before the processing was done.

Release Management

• Affected package(s): Nef_3
• Issue(s) solved (if any): draft/discussion only
• License and copyright ownership: Returned to CGAL authors.

[GilesBathgate]

What I don't like about the PoC is it has to wrap the original info in a value type, and copying that value type is expensive. It also has to any_cast just to check whether the flag is set. So I came up with a possible alternative that could work, but needs to slightly alter the API:

https://gist.github.com/GilesBathgate/8ac8e314df53ec844e385ebd56ff071d