#10667: Morphisms and Objects of Categories
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Reporter: SimonKing | Owner: nthiery
Type: enhancement | Status: needs_work
Priority: major | Milestone: sage-5.0
Component: categories | Keywords: objects morphisms
containment
Work_issues: Cartesian products | Upstream: N/A
Reviewer: | Author: Simon King
Merged: | Dependencies: #9138, #11115, #11780
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Comment(by nthiery):
Replying to [comment:51 SimonKing]:
> First of all, Homsets ''are'' cached. But using unique representation,
it is less easy to break the cache.
I am glad that UniqueRepresentation works well :-)
> And I think that we should use any opportunity to reduce the number of
violations of the unique parent assumption. After all, it is a matter of
efficiency.
Agreed, the more unique parents, the better. But you don't have to fix
all of Sage misfeatures in just this patch :-)
Besides, I am still not yet sure that we want to strictly enforce 100%
unique parents. There might be occasional exceptions -- I don't know,
things like temporarily created parents or what not -- where we might
want to not have uniqueness.
> Actually it was. The problem was that (for the sake of explicit
> documentation) some tests create a polynomial ring directly, not
> using the `PolynomialRing` constructor. My solution: I introduced a
> parent method for rings, that removes the ring from the homset
> cache, and use it after any test that creates a non-unique
> parent. Of course, it is for internal use only.
Ok. I could see other use cases. Should this be a method of
UniqueRepresentation -- of course still for internal use ?
Cheers,
Nicolas
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/10667#comment:52>
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