All permutations

[mdznr]

Description

This addition adds the ability to easily get permutations of a range of sizes, instead of the previous behavior of a single, fixed size, k, like #51 did for Combinations.

Detailed Design

The permutations(ofCount:) function that takes a RangeExpression is added in an extension of Collection.

extension Collection {
  public func permutations<R: RangeExpression>(
    ofCount kRange: R
  ) -> Permutations<Self> where R.Bound == Int {
    return Permutations(self, kRange: kRange)
  }
}

If the upper bound of the range exceeds the length of the collection, no such permutations of those sizes will be returned, effectively clamping the range to 0...n where n is the length of the collection.

Naming

The name permutations(ofCount:) is the same as the original, but reflects the ability to provide multiple counts. This is the same pattern used for Combinations.

Documentation Plan

The documentation in Guides/Permutations.md has been updated to reflect the new function. Inline code documentation also exists for each of the functions.

Test Plan

• Adds tests for the outputs of a range of sizes
• Adds tests for ranges extending above the size of the collection

Source Impact

The functionality is purely additive. The behavior of the existing function is unchanged.

Checklist

• I've added at least one test that validates that my change is working, if appropriate
• I've followed the code style of the rest of the project
• I've read the Contribution Guidelines
• I've updated the documentation if necessary

[kylemacomber]

@mdznr Oh I see this is still a draft, let us know when you're ready for us to review it!

[mdznr]

@mdznr Oh I see this is still a draft, let us know when you're ready for us to review it!

I unfortunately haven’t had a lot of time to work on this. The change is very nearly done. It works. The only things left for me was to ensure it was as well-written as it could be, the implementation consistent with Combinations as much as possible, and the set of unit tests are thorough. I was hoping to really dive into those and ensure it was up to standards before asking others to review.

[timvermeulen]

Thanks a lot for your contribution, @mdznr! This looks very solid, I just have one remark. Feel free to make any other changes you still want to make, but I'm down to get this merged in its current state (modulo that remark).