#15718: Implement the __init_extra__ protocol of categories for Cython classes.
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Reporter: nthiery | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-6.4
Component: categories | Resolution:
Keywords: | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: | Stopgaps:
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Comment (by SimonKing):
Very strange. The following does not work, even in Python:
{{{
sage: from sage.structure.element import RingElement
sage: class E(RingElement):
....: def __init__(self, P, n):
....: self.n = n
....: RingElement.__init__(self, P)
....: def _repr_(self):
....: return "<{}>".format(self.n)
....: def _mul_(self, other):
....: return self.parent()(self.n*other.n)
....: def _add_(self, other):
....: return self.parent()(self.n+other.n)
....: def _lmul_(self, other):
....: return self.parent()(self.n*other)
sage: class P(Parent):
....: Element = E
sage: p = P(base=ZZ, category=Algebras(ZZ))
sage: p.has_coerce_map_from(ZZ)
False
}}}
I found that `UnitalAlgebras.ParentMethods.__init_extra__` is called.
However, it is claimed that the (absence of a) coerce map from ZZ has
already been cached, which means that the clearly existing coercion via
multiplication with `p.one()` is not registered.
At what point is a coercion from ZZ requested *before* calling
`__init_extra__`?
--
Ticket URL: <http://trac.sagemath.org/ticket/15718#comment:18>
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