Opened 9 years ago
Closed 9 years ago
#8702 closed enhancement (fixed)
Datastructure for objects with prototype (clone) design pattern.
Reported by: | hivert | Owned by: | hivert |
---|---|---|---|
Priority: | major | Milestone: | sage-4.6.2 |
Component: | combinatorics | Keywords: | |
Cc: | novoselt, mhansen, sage-combinat | Merged in: | sage-4.6.2.alpha0 |
Authors: | Florent Hivert | Reviewers: | Mike Hansen |
Report Upstream: | N/A | Work issues: | |
Branch: | Commit: | ||
Dependencies: | Stopgaps: |
Description (last modified by )
The idea is inspired from the "prototype" design pattern (see [Pro], [GOF]).
I want to define subclasses of Element with the following behavior: Those classes are intended to be used to model *mathematical* objects, which are by essence immutable. However, in many occasions, one wants to construct the data-structure encoding of a new mathematical object by small modifications of the data structure encoding some already built object. This is a very common stuff for example in matrices: For example: given a matrix M we want to replace every non_zero position by 1
res = copy(M) for pos in res._nonzero_positions_by_row(): res[pos] = 1 res.set_immutable()
However in many cases, for the resulting data-structure to correctly encode the mathematical object, some structural invariants must hold (say for example we want that the matrix is symmetric). One problem is that, in many cases, during the modification process, there is no possibility but to break the invariants. Here there is no way to keep the matrix symmetric during the replacement by 1...
A typical example in combinatorics, in a list modeling a permutation of {1,...,n}, the integers must be distinct. A very common operation is to take a permutation to make a copy with some small modifications, like exchanging two consecutive values in the list or cycling some values. Though the result is clearly a permutations there's no way to avoid breaking the permutations invariants at some point during the modifications.
So the idea is the following: to allows local breaking of invariant on a
locally mutable copy and to check that things are restored in a proper state
at the end. So I wrote a small class called ClonableElement
and several
derived subclasses (clone is the standard name for the copy method in the
"prototype" design pattern):
A class C inheriting from ClonableElement? must implement the following two methods
- obj.__copy__() -- returns a fresh copy of obj - obj.check() -- returns nothing, raise an exception if obj doesn't satisfies the data structure invariants
Then, given an instance obj of C, the following sequences of instructions ensures that the invariants of new_obj are properly restored at the end
with obj.clone() as new_obj: ... # lot of invariant breaking modifications on new_obj ... # invariants are ensured to be fulfilled
The following equivalent sequence of instructions can be used if speed is needed, in particular in Cython code (unfortunately, the handling of the with instruction make some overhead)...
new_obj = obj.__copy__() ... # lot of invariant breaking modifications on new_obj ... new_obj.set_immutable() new_obj.check() # invariants are ensured to be fulfilled
I also took to chance to handle hashing...
This is the future Cython replacement for CombinatorialObject.
[Pro] Prototype pattern http://en.wikipedia.org/wiki/Prototype_pattern
[GOF] Design Patterns: Elements of Reusable Object-Oriented Software. E. Gamma; R. Helm; R. Johnson; J. Vlissides (1994). Addison-Wesley. ISBN 0-201-63361-2.
Attachments (3)
Change History (17)
comment:1 Changed 9 years ago by
- Status changed from new to needs_review
comment:2 Changed 9 years ago by
- Cc novoselt added
- Milestone set to sage-4.4.4
- Type changed from defect to enhancement
comment:3 Changed 9 years ago by
- Description modified (diff)
comment:4 follow-up: ↓ 5 Changed 9 years ago by
- Cc mhansen added
- Reviewers set to Mike Hansen
comment:5 in reply to: ↑ 4 Changed 9 years ago by
and updated a new patch... Please review.
Sorry: I should have said that I also folded your review patch... Thanks for it.
comment:6 follow-up: ↓ 7 Changed 9 years ago by
- Status changed from needs_review to positive_review
Looks good to me.
comment:7 in reply to: ↑ 6 Changed 9 years ago by
comment:8 follow-up: ↓ 9 Changed 9 years ago by
- Status changed from positive_review to needs_work
I get doctest errors:
********************************************************************** File "/mnt/usb1/scratch/jdemeyer/merger/sage-4.6.1.alpha1/devel/sage-main/sage/structure/list_clone_timings.py", line 8: sage: from sage.structure.list_clone_timmings import * Exception raised: Traceback (most recent call last): File "/mnt/usb1/scratch/jdemeyer/merger/sage-4.6.1.alpha1/local/bin/ncadoctest.py", line 1231, in run_one_test self.run_one_example(test, example, filename, compileflags) File "/mnt/usb1/scratch/jdemeyer/merger/sage-4.6.1.alpha1/local/bin/sagedoctest.py", line 38, in run_one_example OrigDocTestRunner.run_one_example(self, test, example, filename, compileflags) File "/mnt/usb1/scratch/jdemeyer/merger/sage-4.6.1.alpha1/local/bin/ncadoctest.py", line 1172, in run_one_example compileflags, 1) in test.globs File "<doctest __main__.example_0[2]>", line 1, in <module> from sage.structure.list_clone_timmings import *###line 8: sage: from sage.structure.list_clone_timmings import * ImportError: No module named list_clone_timmings **********************************************************************
Changed 9 years ago by
comment:9 in reply to: ↑ 8 Changed 9 years ago by
- Status changed from needs_work to needs_review
Replying to jdemeyer:
I get doctest errors:
********************************************************************** File "/mnt/usb1/scratch/jdemeyer/merger/sage-4.6.1.alpha1/devel/sage-main/sage/structure/list_clone_timings.py", line 8: sage: from sage.structure.list_clone_timmings import * [...]
Oups ! I forgot to fold some corrective patches. I just resubmitted the corrected version. To ease the review I also uploaded the diff between the older version and the new one. Do not apply this chunk of code.
Only apply trac_8702-list_clone-fh.patch
Changed 9 years ago by
comment:10 Changed 9 years ago by
Added a missing utf8 tag on the file list_clone_timings.py
...
Apply only trac_8702-list_clone-fh.2.patch
Changed 9 years ago by
comment:11 Changed 9 years ago by
Oops ! I forgot to add Copyright notices... Sorry for the mess.
Apply only trac_8702-list_clone-fh.patch
comment:12 Changed 9 years ago by
- Cc sage-combinat added
- Status changed from needs_review to positive_review
comment:13 Changed 9 years ago by
- Milestone changed from sage-4.6.1 to sage-4.6.2
comment:14 Changed 9 years ago by
- Merged in set to sage-4.6.2.alpha0
- Resolution set to fixed
- Status changed from positive_review to closed
Hi mike,
I adressed your comment:
and updated a new patch... Please review.