Remove and cleanup functions in std::vec #9062
Conversation
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forgot to put the test in the correct spot in the file. Fixing that.. |
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This... is awesome. I'd be willing to r+ as-is, but I wanted to ask one question first:
I was also thinking we could make |
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using a function or method instead of a |
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With these revelations, the new permutation iterator isn't much better than the old. An internal iteration function could encapsulate the efficient version however. |
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For what it's worth, this still seems better to me because it doesn't have any recursion and you can weave it with other iterators. It may not be able to drop |
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It's not what it's supposed to be, but I think it's ready, now in the form of |
Remove unzip_slice since it's redundant. Old unzip is equivalent to the `|x| unzip(x.move_iter())`
Introduce ElementSwaps and Permutations. ElementSwaps is an iterator
that for a given sequence length yields the element swaps needed
to visit each possible permutation of the sequence in turn.
We use an algorithm that generates a sequence such that each permutation
is only one swap apart.
let mut v = [1, 2, 3];
for perm in v.permutations_iter() {
// yields 1 2 3 | 1 3 2 | 3 1 2 | 3 2 1 | 2 3 1 | 2 1 3
}
The `.permutations_iter()` yields clones of the input vector for each
permutation.
If a copyless traversal is needed, it can be constructed with
`ElementSwaps`:
for (a, b) in ElementSwaps::new(3) {
// yields (2, 1), (1, 0), (2, 1) ...
v.swap(a, b);
// ..
}
Update for a lot of changes (not many free functions left), add examples of the important methods `slice` and `push`, and write a short bit about iteration.
The basic construct x.len() == y.len() is just as simple. This function used to be a precondition (not sure about the terminology), so it had to be a function. This is not relevant any more.
These functions have very few users since they are mostly replaced by iterator-based constructions. Convert a few remaining users in-tree, and reduce the number of functions by basically renaming build_sized_opt to build, and removing the other two. This for both the vec and the at_vec versions.
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I squashed together the permutation_iter changes, I updated the PR description title and text. A small diff from before the squash: I changed the text in the std::vec module doc slightly and added an assert to the test for ElementSwaps. |
Visit the free functions of std::vec and reimplement or remove some. Most prominently, remove `each_permutation` and replace with two iterators, ElementSwaps and Permutations. Replace unzip, unzip_slice with an updated `unzip` that works with an iterator argument. Replace each_permutation with a Permutation iterator. The new permutation iterator is more efficient since it uses an algorithm that produces permutations in an order where each is only one element swap apart, including swapping back to the original state with one swap at the end. Unify the seldomly used functions `build`, `build_sized`, `build_sized_opt` into just one function `build`. Remove `equal_sizes`
Visit the free functions of std::vec and reimplement or remove some. Most prominently, remove
each_permutationand replace with two iterators, ElementSwaps and Permutations.Replace unzip, unzip_slice with an updated
unzipthat works with an iterator argument.Replace each_permutation with a Permutation iterator. The new permutation iterator is more efficient since it uses an algorithm that produces permutations in an order where each is only one element swap apart, including swapping back to the original state with one swap at the end.
Unify the seldomly used functions
build,build_sized,build_sized_optinto just one functionbuild.Remove
equal_sizes