#14535: Mutability of Graphs
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Reporter: SimonKing | Owner: jason, ncohen, rlm
Type: enhancement | Status: needs_review
Priority: major | Milestone: sage-5.10
Component: graph theory | Resolution:
Keywords: mutability graph | Work issues:
Report Upstream: N/A | Reviewers:
Authors: Simon King | Merged in:
Dependencies: #14524 | Stopgaps:
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Comment (by SimonKing):
Replying to [comment:8 ncohen]:
> > There certainly is a slowdown in all methods that are protected in
this way. And I do not use the decorator in cdef classes, in an attempt to
prevent a regression.
>
> Hmmmm. And why should we accept a 10% slowdown in order to have
immutable graphs ? `:-P`
It would be nice to have a better solution, but, as for matrices, I do
think it would be good to be able to use graphs as keys in dictionaries
''without'' a hack.
> > I do not forbid to change the graphs in the backend. Or at least, I
did not intend to modify the backends. If I did, then it was by mistake.
If G is an immutable graph, then `G._backend.add_vertex(...)` should not
complain.
>
> ? But you make changes to `CGraph`, `SparseGraph` and `DenseGraph`,
don't you ? `O_o`
Then we may have different notions of "backend". By "backend", I
understood the stuff that is assigned to `G._backend` and is defined in
sage.graphs.base.graph_backends`.
You think it might be better to move all mutability checks into the
backend? I thought so as well, initially. But then I found that a couple
of add_* methods first change some data ''outside'' of the backend, and
call the backend method only later. So, I thought it is safer to check
mutability not in the backend, but in the graph.
> Hmmmm... But the developpers could have to do that to make some methods
more efficient, and then we would have to deal with immutability by hand.
But really I am interested in your answer : why don't you prefer to deal
with immutability in the backends directly ? In the `graphs/base/` files ?
I would prefer to deal with it in the backends.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/14535#comment:9>
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