#7421: Weaker precondition for registering a new coercion.
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Reporter: nthiery | Owner: robertwb
Type: enhancement | Status: needs_review
Priority: blocker | Milestone: sage-4.2.1
Component: coercion | Keywords: coercion
Work_issues: | Author: Nicolas M. Thiéry
Reviewer: Robert Bradshaw | Merged:
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Description changed by nthiery:
Old description:
> With the attached patch, the precondition for registering a new
> coercion from P to Q with register_coercion becomes:
>
> "no over coercion from P to Q has been registered or discovered earlier"
>
> Which is a bit weaker than the previous:
>
> "no coercion into P has been queried"
>
> This should still be quite safe, while covering all the formerly
> problematic practical use cases coming up in the category code #5981.
New description:
With the attached patch, the precondition for registering a new
coercion from P to Q with register_coercion becomes:
"no coercion into P has been queried, or no coercion from P to Q has been
registered or discovered earlier"
Which is a bit weaker than the previous:
"no coercion into P has been queried"
This should still be quite safe, while covering all the formerly
problematic practical use cases coming up in the category code #5981.
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/7421#comment:5>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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