entity set implementation for iMesh and iGeom

[Mark Beall]

Are the behaviors you describe documented somewhere? We had a number  
of questions on how the entity sets are supposed to behave with the  
boolean ops that we couldn't find answers to.

Thanks,
mark


On Nov 5, 2009, at 10:25 AM, Carl Ollivier-Gooch wrote:

> Ottmar Klaas wrote:
>> Hi,
>> while looking at implementing entity sets, we ran into a few  
>> questions, and I was wondering if someone could help us sort this  
>> out. According to the documentation of iMesh/iGeom entity sets can  
>> be ordered or unordered. Based on what we could find in the  
>> documentation, the only differentiator between the two sets is that  
>> "Unordered entity sets can contain a given entity or set only  
>> once", opening up a variety of possible implementations for ordered  
>> sets. However, the naming of parameters (e.g. int isList) to  
>> differentiate between ordered and unordered sets seems to imply  
>> that ordered sets are to be implemented based on a list data  
>> structure. We were wondering if you can give us more information  
>> regarding the requirements for the entity set implementation. Is  
>> your intention to prescribe the implementation (classical list data  
>> structure for ordered sets, and a set data structure for unordered  
>> sets)? If not, could you define the requirements for the entity set  
>> implementations, e.g. how fast is random access supposed to be  
>> (e.g. O(n) or faster), are ordered sets order preserving in the  
>> sense that the order in which I add entities to an ordered set is  
>> the order in which the iterator will return the entities, etc.?
>
> While STL lists and sets are possibilities for implementation, you  
> can do them some other way if you prefer.
>
> There is no performance spec (in particular, iMesh sets don't  
> support random access, so definitely no spec there).
>
> The distinguishing feature is the one you asked about:  an iterator  
> has to return the entities in the order added.  Also, boolean ops on  
> two ordered sets have prescribed behavior (boolean ops on one  
> ordered and one unordered set behave as if both were unordered).  I  
> seem to recall that removing an entity that appears multiple times  
> in an ordered set removes the -last- copy, but that might be wrong...
>
> Cheers,
> Carl
>
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