#18529: Topological manifolds: basics
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Reporter: egourgoulhon | Owner: egourgoulhon
Type: enhancement | Status: needs_info
Priority: major | Milestone: sage-7.0
Component: geometry | Resolution:
Keywords: topological | Merged in:
manifolds | Reviewers: Travis Scrimshaw
Authors: Eric Gourgoulhon, | Work issues:
Travis Scrimshaw | Commit:
Report Upstream: N/A | 3cd03a48d847e12745ed8c25b23f19db141c179a
Branch: | Stopgaps:
public/manifolds/top_manif_basics |
Dependencies: #18175 |
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Comment (by tscrim):
There are 2 really, really good ideas for having a more complicated class
hierarchy: encapsulation and localization.
You had many `if self._manifold is self:` statements, which breaks the
localization principle; it is acting differently because it is essentially
a different object. This is a strong code smell and you had enough of
these at this level to (IMO) warrant splitting the classes.
Additionally, subsets of a manifold are precisely that, subsets. So we
should encapsulate that in separate classes. Mathematically we identity an
open subset as a manifold, but by doing so, we loose the information that
it is really a subset of another manifold. As such, I feel that having
separate classes actually better reflects the mathematics.
In an ideal world, I would like to have a hierarchy similar to Hierachy-2,
but with an additional subclass corresponding to each type of manifold
that is obtained by adding a subset mixin class. Yet, that doesn't seem
possible with the current core design.
While the Hierarchy-1 seems more complicated, it actually will be easier
to maintain and debug as code is local to the class (i.e., if you are a
subclass of `A`, then you act in the same way and like `A` irregardless of
your input).
This assessment is based on my experiences and what I learned as good OOP
principles. However, I have not looked at !SageManifolds beyond this
ticket at present, whereas you have worked heavily on it. So perhaps we
can get some more data. How many times before the refactoring did you have
to do a `self._manifold is self` test? Also what is your thoughts on
maintenance and extendability?
Something else might be to get a 3rd party's opinion (Nicolas and/or Darij
comes to my mind). I could also sit down and plan out how I would do
everything from the ground up to see if I can devise a better overall
strategy if you think there might be some benefit to that at this stage.
--
Ticket URL: <http://trac.sagemath.org/ticket/18529#comment:108>
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