如何从 ClosedRange.SubSequence 中删除 Slice<>？

Question

I'm using the chunked method in Swift Algorithms .

When I work on a Range, it's pretty easy to handle the resulting type:

let range: Range<Int> = 0..<5
let subRangesIntermediary: [Range<Int>.SubSequence] = range.chunked(on: { $0 / 2 })
assert(Range<Int>.SubSequence.self == Range<Int>.self)

let subRanges: [Range<Int>] = subRangesIntermediary
assert(subRanges == [0..<2, 2..<4, 4..<5])

That's because Range<Int>.SubSequence == Range<Int> so converting between the two is effortless.

When I try to do the same thing with ClosedRange , I run into problems:

let closedRange: ClosedRange<Int> = 0...4
let subClosedRangesIntermediary: [ClosedRange<Int>.SubSequence] = closedRange.chunked(on: { $0 / 2})
let subClosedRangesIntermediary2: [Slice<ClosedRange<Int>>] = subClosedRangesIntermediary
// assert(subClosedRangesIntermediary2 == [0...1, 2...3, 4...4]) // ❌ Binary operator '==' cannot be applied to operands of type '[Slice<ClosedRange<Int>>]' and 'ArraySlice<ClosedRange<Int>>'

That's because ClosedRange<Int>.SubSequence == Slice<ClosedRange<Int>> .

I'm looking to remove the Slice so that I'm left with an array of ClosedRange .

I figured out a way to do it manually, but this looks like a lot of work:

let subClosedRanges: [ClosedRange<Int>] = subClosedRangesIntermediary2.map {
  let start = closedRange[$0.startIndex]
  let end = closedRange[$0.index(before: $0.endIndex)]
  return start...end
}
assert(subClosedRanges == [0...1, 2...3, 4...4])

I was hoping there is a way to do something like the following instead:

let subClosedRanges: [ClosedRange<Int>] = subClosedRangesIntermediary2.map { $0.valueInBase }

or:

// Similar to how we can use Array(slice) on ArraySlice:
let subClosedRanges: [ClosedRange<Int>] = subClosedRangesIntermediary2.map { ClosedRange($0) }

I couldn't find anything like that for Slice .

How do I convert a Slice<ClosedRange<T>> to a ClosedRange<T> ?

Answer 1

Barring a more authoritative answer, here is a workaround:

extension ClosedRange where Bound: Strideable, Bound.Stride: SignedInteger {
  init(_ slice: Slice<Self>) {
    let lower = slice.base[slice.startIndex]
    let upper = slice.base[slice.index(before: slice.endIndex)]
    self.init(uncheckedBounds: (lower: lower, upper: upper))
  }
}

Usage:

let subClosedRanges: [ClosedRange<Int>] = subClosedRangesIntermediary2.map { ClosedRange($0) }