#10130: Revamp __hash__, __cmp__ and __richcmp__
---------------------------+------------------------------------------------
Reporter: roed | Owner: robertwb
Type: enhancement | Status: new
Priority: major | Milestone: sage-4.6.1
Component: coercion | Keywords:
Author: | Upstream: N/A
Reviewer: | Merged:
Work_issues: |
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Comment(by roed):
I don't know the best way to resolve these issues, but here are some
ideas.
* Have cpdef'd functions `_hash_`, `_cmp_` and `_richcmp_` that users
will override.
* For parents, add an attribute "cdef public long `__hash`". I don't
know if this should be set to self._hash_() during the parent's `__init__`
method, or set to -1 and then reset upon the first call to `__hash__`.
* For `SageObject`, have the default behavior of `_hash_()` be to return
`hash(repr(self))`. For parents, have the default value of hash depend on
`self.construction()`?
* For elements, don't cache the hash by default.
* Have the results of ==, <, etc, depend on `_richcmp_`. By default,
have `_richcmp_` determined by a total ordering implemented by `_cmp_`.
So if you want to have partial ordering, or a different partial and total
ordering, you need to implement both `_cmp_` and `_richcmp_`.
* For parents, `_cmp_` checks first for pointer equality. If non-equal,
it compares the hashes. If those are nonequal, returns the cmp of the
hashes. Otherwise, returns the cmp of the pointers.
* Elements would have no default `_cmp_`, but would instead raise an
error.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/10130#comment:1>
Sage <http://www.sagemath.org>
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