I think we should be able to do away with the unsafe code. I'll take a
look and get back to you.
Niko
Ben Alpert wrote:
Hi all,
I was perusing the source code of vec::each_permutation and noticed the comment:
This does not seem like the most efficient implementation. You
could make far fewer copies if you put your mind to it.
so I decided to try my hand at a faster version, which I have posted here:
https://gist.github.com/48b14f37051e7b91c22c
Code review would be appreciated. In particular, I did some awkward
shenanigans to pass v around my recursive function called 'helper' in
order to satisfy the ownership checker. Originally I had helper(v:
&mut [T], ...) -> bool, but that causes an error because put takes a
&[T]. It would be great if there was a simpler way to do this.
For comparison, it seems to be around 100x faster on this trivial test:
let mut i = 0;
for each_permutation(~[1,2,3,4,5,6,7,8,9,10,11]) |_| { i += 1; }
assert i == 39916800;
Let me know whether it makes sense to open a pull request with this
new implementation.
Thanks,
Ben
P.S. I am puzzled by the fact that each_permutation is listed in the
docs but it's not marked as pub so it appears to be inaccessible from
outside the vec.rs file.
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