#12048: FiniteEnumeratedSet creates elements that don't inherit from Element
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Reporter: roed | Owner: sage-combinat
Type: defect | Status: needs_work
Priority: major | Milestone: sage-5.1
Component: combinatorics | Resolution:
Keywords: | Work issues:
Report Upstream: N/A | Reviewers:
Authors: David Roe | Merged in:
Dependencies: | Stopgaps:
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Comment (by nthiery):
Dear David,
Sorry for lagging so much behind on this ticket. I have finally been
discussing with Florent, and we agreed on the following:
- We definitely want to have facade parents in Sage whose elements
are plain Python objects. In fact we already have some: you can
e.g. define facade posets on strings or
sage.structure.parent.Set_PythonType(int).
Under many circumstances, wrapping objects sure has its advantages
(the element can make use of the parent information for certain
operations), but there are also many use cases where constantly
wrapping/unwrapping is a pain.
The worst is when a user gives a list of objects as input to
construct some parent A (e.g. a CombinatorialFreeModule), and then
(s)he accesses those objects from A he gets something that looks
and smell like the original objects but differ in behavior in a
subtle way
- Coercion should work for those parents. It does not currently due
to this test whether the end result of __call__ is an Element. This
should be easy to fix. We already got hurt by that with Posets, and
had to resort to a hand made __call__ (yuck).
- By default, we prefer FiniteEnumeratedSets to be facades by default
to not break backward compatibility, and also because this seems to
be what we need most of the time (because there are barely no
operations on the elements).
. Now if there is a clear need for it, we could add a facade
option to have non facade FiniteEnumeratedSets.
What do you think? Do you feel like fixing coercion as above?
Cheers,
Nicolas
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/12048#comment:9>
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