#14249: There should be no need to have _an_element_ implement to multiply
elements
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Reporter: SimonKing | Owner: robertwb
Type: defect | Status: needs_review
Priority: major | Milestone: sage-5.9
Component: coercion | Resolution:
Keywords: | Work issues:
Report Upstream: N/A | Reviewers:
Authors: Simon King | Merged in:
Dependencies: #14264 | Stopgaps:
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Comment (by SimonKing):
Replying to [comment:2 nbruin]:
> Isn't it a logical flaw that there should even be elements for an action
to exist?
For ''general'' actions I agree. But:
> This particular scenario isn't particularly relevant for the coercion
framework, but it does show that actions on empty sets are natural to
consider, so if we're not supporting that, there may be something wrong
with our model.
Don't forget that what we are talking about here is in
sage.structure.coerce_actions. So, this ''is'' for coercions, and it
''is'' to be applied to elements.
sage.categories.action is of course more general.
> Can't we just ditch the sanity check (or skip it if an element isn't
easily obtained)?
Part of the problem is that we have different ways to define an action on
elements. There is _rmul_/_lmul_, there is _l_action/_r_action (at least
according to sage.structure.coerce_actions, but it isn't used in
sage.structure.coerce), there is _act_on_, and there is _acted_upon_.
Moreover, there is `IntegerMulAction`. And since they are all acting ''on
elements'', I think it somehow does make sense to test which of the
different flavours is available for the elements.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/14249#comment:3>
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