#15303: Coercion discovery fails to be transitive
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Reporter: nbruin | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-5.13
Component: coercion | Resolution:
Keywords: | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: #14711 | Stopgaps:
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Comment (by SimonKing):
With the branch that I have just attached, one gets
{{{
sage: class pA(Parent): pass
sage: class pB(Parent): pass
sage: class pC(Parent): pass
sage:
sage: A=pA(); B=pB(); C=pC()
sage:
sage: BtoA=Hom(B,A)(lambda x: A(x))
sage: AtoC=Hom(A,C)(lambda x: C(x))
sage: A.register_coercion(BtoA)
sage: A.register_embedding(AtoC)
sage: C.coerce_map_from(B)
Composite map:
From: <class '__main__.pB'>
To: <class '__main__.pC'>
WARNING: This map has apparently been used internally
in the coercion system. It may become defunct in the next
garbage collection. Please use a copy.
}}}
What has been done in the patch:
- renaming of attributes (`_coerce_from_backtracking` etc)
- do not use a list, but use a `MonoDict` for all morphisms that are
supposed to be fundamental for backtracking. There is a list
`_registered_domains`, so that domains of registered coercions are kept
alive by the codomain, but the domain of a registered embedding is ''not''
kept alive by the codomain.
Missing: Tests and versioning.
--
Ticket URL: <http://trac.sagemath.org/ticket/15303#comment:10>
Sage <http://www.sagemath.org>
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