#15223: Let the `TestSuite` test that the construction of a parent returns the
parent
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Reporter: SimonKing | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-5.12
Component: coercion | Resolution:
Keywords: | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
u/SimonKing/ticket/15223 | a81fcc1072df88cc369d7aa0b7ae423fd97d7f02
Dependencies: | Stopgaps:
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Comment (by nbruin):
Replying to [comment:13 SimonKing]:
> No, it is not !UniqueRepresentation:
> {{{
> sage: isinstance(A,UniqueRepresentation)
> False
> }}}
That doesn't tell the entire story, though:
{{{
sage: type(IntegerModRing).mro()
[sage.rings.finite_rings.integer_mod_ring.IntegerModFactory,
sage.structure.factory.UniqueFactory,
sage.structure.sage_object.SageObject,
object]
}}}
so perhaps the ''object'' isn't really !UniqueRepresentation but the
''system'' tries to implement the semantics via a factory. So I think
you're seeing exactly the problem I was afraid of:
{{{
sage: A1=IntegerModRing(19)
sage: A2=IntegerModRing(19)
sage: B1=IntegerModRing(19,category=Fields())
sage: B2=IntegerModRing(19,category=Fields())
sage: A1 is A2
True
sage: B1 is B2
True
sage: A1 in Fields()
True
sage: type(A1)
<class
'sage.rings.finite_rings.integer_mod_ring.IntegerModRing_generic_with_category'>
sage: type(B1)
<class
'sage.rings.finite_rings.integer_mod_ring.IntegerModRing_generic_with_category'>
sage: type(A1) == type(B1)
False
}}}
so after this we do have two functionally equivalent copies of the same
ring: `A1,B1`, but they are not identical. Furthermore, their types are
not identical or equal either, but it's hard to see what the difference is
between them (note `A1.__cmp__` to see that this last `False` is the
reason why `A1 != B1`.
--
Ticket URL: <http://trac.sagemath.org/ticket/15223#comment:18>
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