#15247: Introduce a baseclass for singletons
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Reporter: SimonKing | Type: enhancement
Status: new | Priority: major
Milestone: sage-5.13 | Component: performance
Resolution: | Report Upstream: N/A
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Since some while, we have
`sage.categories.category_singleton.Category_singleton`. A singleton is a
class that allows the creation of exactly one instance (of any subclass).
The technical implementa
tion of `Category_singleton` is roughly like this: In some static
`__classcall__`, test that the given class is a direct subclass of
`Category_singleton`; then create a (the) instance of the class;
then set the override the classcall of this class and of the class of the
instance (which might be a subclass) by a constant function returning the
instance.
I suggest to provide this construction scheme generally, in
`sage.misc.fast_methods.SingletonClass`. The idea is: If one write a class
inheriting from `SingletonClass` then one does not need to think about
caching the unique instance or writing a fast hash or writing fast
comparison, since this will all be inherited from `SingletonClass`.
I suggest to use it at least on the rational field, which currently has a
custom cache, and its hash method is written in Python.
With the branch that I am going to add, I get
{{{
sage: %timeit RationalField()
1000000 loops, best of 3: 269 ns per loop
sage: %timeit hash(QQ)
10000000 loops, best of 3: 134 ns per loop
sage: %timeit QQ==ZZ
10000000 loops, best of 3: 144 ns per loop
}}}
With vanilla sage-5.12.b5, it is a lot slower:
{{{
sage: %timeit RationalField()
10000 loops, best of 3: 82.4 us per loop
sage: %timeit hash(QQ)
1000000 loops, best of 3: 496 ns per loop
sage: %timeit QQ==ZZ
1000000 loops, best of 3: 878 ns per loop
}}}
--
Ticket URL: <http://trac.sagemath.org/ticket/15247>
Sage <http://www.sagemath.org>
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