#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 SimonKing):
Replying to [comment:12 nthiery]:
> This sounds like a good idea indeed! I would tend to put the test in
> Sets (in the general trend that there is already too much stuff in
> Parent; and maybe construction should be moved there, so as to make it
> easier to overload it, e.g. in some categories).
I am not so sure about this. `.construction()` is one of the places where
mathematics and implementation meet: On the one hand, `.construction()`
returns a functor (or at least something that pretends to be a functor),
which is a mathematical notion. On the other hand, the construction
functors are quite clearly ''also'' responsible for choosing
implementations. For example, the fact that the following pushout uses
''dense'' power series rings is entirely due to construction functors:
{{{
sage: Ps.<x> = PowerSeriesRing(QQ, sparse=True)
sage: Pd.<x> = PowerSeriesRing(ZZ, sparse=False)
sage: Pd['y'].has_coerce_map_from(Ps['y'])
False
sage: pushout(Ps['y'],Pd['y'])
Univariate Polynomial Ring in y over Power Series Ring in x over Rational
Field
sage: pushout(Ps['y'],Pd['y']) == Ps['y']
False
}}}
But if it is (partially) about implementation, then I believe its place is
not in `Sets.ParentMethods`.
> > But when running the tests, it turns out that this is too narrow:
Sometimes, we want to apply the quotient functor F to a ring over a
''different'' base ring.
>
> This does not seem directly related to this ticket. Could this easily
> be split off into a separate ticket?
Probably better. I am actually not sure if it would be a good idea to
modify the quotient functor in that way.
> > Nicolas, do you think it would hurt to introduce such method here?
>
> This seems like a sensible method; so if you have a use for it, go
> ahead.
Not sure yet.
--
Ticket URL: <http://trac.sagemath.org/ticket/15223#comment:14>
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