#11900: Serious regression caused by #9138
----------------------------------------------------------------------------------------+
Reporter: SimonKing
| Owner: tbd
Type: defect
| Status: needs_work
Priority: critical
| Milestone: sage-4.8
Component: performance
| Keywords: categories regression
Work_issues: Laurent series rings are fields. Add docs. Don't use is_ring and
friends | Upstream: N/A
Reviewer: Jeroen Demeyer, Nicolas M. Thiéry
| Author: Simon King
Merged:
| Dependencies: #9138 #11911
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Comment(by SimonKing):
There is something wrong with Category_singleton: It cant' be subclassed.
{{{
sage: class Test(Rings):
....: pass
....:
sage: T = Test()
sage: T
Category of rings
}}}
In other words, making `__classcall__` a lazy class attribute won't work,
since subclasses need a different `__classcall__`.
Or do you see a mechanism that allows for subclassing?
The problem occurs if one makes `EnumeratedSets` inherit from
Category_singleton, since `DeBruijnSequences` subclass enumerated sets.
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/11900#comment:121>
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