#4740: avoid creating unneeded homsets when coercing
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Reporter: mabshoff | Owner: robertwb
Type: defect | Status: needs_work
Priority: major | Milestone: sage-5.11
Component: memleak | Resolution:
Keywords: | Merged in:
Authors: Mike Hansen | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Dependencies:
Stopgaps: |
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Changes (by SimonKing):
* status: needs_review => needs_work
Comment:
Replying to [comment:9 mhansen]:
> Simon -- see any issues here?
Yes, and a quite severe issue.
The problem is, as often, unique versus non-unique parent structures. For
coercion, we need that the domain and codomain of a coercion from A to B
are not just equal but identical to A and B. But with
`UniqueRepresentation`, the given input arguments are compared by
equality, not by identity. That's why it was a conscious decision to use
`TripleDict` for caching homsets.
The cache is provided by the `Hom()` function in sage.categories.homset.
If homsets are really created over and over again, then there seems to be
a rogue call to `Homset(...)`. The solution is not to make `Homset` a
cached class, but to call the `Hom()` function instead.
--
Ticket URL: <http://trac.sagemath.org/ticket/4740#comment:12>
Sage <http://www.sagemath.org>
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