#14793: Unique representation for homsets
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Reporter: nthiery | Owner: nthiery
Type: enhancement | Status: new
Priority: major | Milestone: sage-5.12
Component: categories | Resolution:
Keywords: | Work issues:
Report Upstream: N/A | Reviewers:
Authors: Simon King | Merged in:
Dependencies: | Stopgaps:
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Comment (by SimonKing):
It is a can of worms. The problem will always arise under the following
conditions:
- We have `Homset.__reduce__` returning `Hom, (self._domain,
self._codomain, self.__category)`
- We have a parent X whose pickling is done via pickling `__dict__` using
the default Python way
- `Hom(X,X)` (or any other homset involving X) is stored in `X.__dict__`.
In this situation, unpickling X means that we have an uninitialised copy Y
of X and want to call Hom(Y,Y).
My previous suggestion was: "In Hom(X,Y,cat), if X.category() fails and
cat is given, then trust that X will eventually become sufficiently
initialised to see that X is in cat".
Perhaps a modified suggestion is better: "In Hom(X,Y,cat), if X.category()
fails, then at least test that X.__class__ is a subclass of
cat.parent_class." This test is almost as good as `X in cat`, namely
yields the same result unless a base ring is involved.
Do you have a better suggestion? I really would not like to implement
`__reduce__` methods everywhere in sage.schemes and sage.modular.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/14793#comment:21>
Sage <http://www.sagemath.org>
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