It’s been a while, the language has evolved, and so I thought I’d visit my old friend the PermutationGenerator. Header docs say:
A *generator* that adapts a *collection* `C` and any *sequence* of its `Index` type to present the collection’s elements in a permuted order.
You pass it a collection and a sequence of indices, and it returns elements based on that sequence. This code creates a scrambled index generator, which I feed to AnySequence to build the permuted output.
The permutation generator isn’t limited to random scrambles. You can use the same approach to build a strideable sequence as in this next snippet, or to any other computed walk through indices:
I had to tweak a bit with the distance check because you cannot use < to test two Self.Index operands. Update: Much improved. Thanks @oisdk.
While I don’t see myself using this a lot, I’m glad I had the chance to swing by it a second time for another look. As always, feel free to correct, tweak, or improve. Thanks!
@ericasadun advancedBy has a limit parameter, so you can avoid the O(n) distanceTo() and <. https://t.co/ELohbRKdSj pic.twitter.com/NbjIdFL8k4
— oisdk (@oisdk) September 15, 2015
2 Comments
This is the worst named method Apple has created. It’s *not* a PermutationGenerator. It’s a ObjectsAtIndexes generator. I have a bug on this, and they even acknowledged that it wasn’t named right, but now it’s probably too late for them to change it.
PermutationGenerator has been deprecated in Swift 2.2 and will be removed in Swift 3.