#14912: UniqueRepresentation tutorial could use more love
--------------------------------------------+--------------------
Reporter: darij | Owner:
Type: defect | Status: new
Priority: major | Milestone:
Component: documentation | Resolution:
Keywords: documentation, structure | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Dependencies:
Stopgaps: |
--------------------------------------------+--------------------
Comment (by SimonKing):
I think both `sage.structure.unique_representation` and
`sage.structure.factory` need more care.
Certainly it is a severe fault that `GF(...)` appears as example of
`UniqueRepresentation`.
And I think both parts of the documentation should give hints on when to
use `UniqueRepresentation` and when to use `UniqueFactory`.
For example, a `UniqueFactory` can return different implementations of the
same algebraic structure, depending on the input data. This would be
impossible (or at least not so easily possible) with
`UniqueRepresentation`. And you would not be able to use
`UniqueRepresentation` with a cdef class---you can define your class in a
pyx file, but it has to be `class Foo(UniqueRepresentation, ...)`, not
`cdef class Foo(UniqueRepresentation, ...)`, simply since
`UniqueRepresentation` uses meta-classes, which is not possible in a cdef
class, if I am not mistaken (and of course, multiple inheritance does not
work yet in Cython, and after all `UniqueRepresentation` is a python
class.
These are reasons for using a factory.
On the other hand, using `UniqueRepresentation` would automatically
provide your class with very fast hash and comparison methods implemented
in Cython (`UniqueRepresentation` is a Python class, but also inherits
from the Cython class `sage.misc.fast_methods.WithEqualityById`). If you
use a factory instead, you'd need to take care of hash and comparison all
by yourself---and this means: It is possible that a `UniqueFactory`
returns objects that are ''not'' unique parents!! And moreover, using
`UniqueRepresentation` is very easy---in most cases, it is enough to take
an existing class and add `UniqueRepresentation` as base.
So, these are reasons for using a unique representation.
--
Ticket URL: <http://trac.sagemath.org/ticket/14912#comment:7>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
--
You received this message because you are subscribed to the Google Groups
"sage-trac" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To post to this group, send email to [email protected].
Visit this group at http://groups.google.com/group/sage-trac.
For more options, visit https://groups.google.com/groups/opt_out.
