On Tue, May 05, 2015 at 10:41:42AM +0200, Jeroen Demeyer wrote:
> what are the types CategoryObject and Parent supposed to represent? For
> example, I don't understand why generators and names are dealt with on the
> level of CategoryObject but constructing elements is dealt with on the level
> of Parent.
> In fact, in all of Sage, there is only a single class which is a
> CategoryObject but not a Parent:
>
> class SimplicialComplex(CategoryObject, GenericCellComplex)
Parents are supposed to model sets (typically with some structure),
when CategoryObject can be more general. Simplicial complexes are
typical examples, where we want to model instead a collection of sets
with some structure. This feature has indeed not been used much yet
(which also reflects in the fact that almost all categories are
subcategories of `Sets()` rather than of `Objects()`).
Very much like for Parent, there probably are things that are in
CategoryObject for very old legacy reasons (typically pre-categories!)
and really do not belong there; this could typically be the case for
generators and names.
Cheers,
Nicolas
--
Nicolas M. Thiéry "Isil" <[email protected]>
http://Nicolas.Thiery.name/
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