each_cons from Ruby in Swift as a function on Sequence

Array+EachCons.swift

extension Collection {
    func eachConsecutive(_ size: Int) -> Array<SubSequence> {
        let droppedIndices = indices.dropFirst(size - 1)
        return zip(indices, droppedIndices)
            .map { return self[$0...$1] }
    }
}

Sequence+EachPair.swift

extension Sequence {
  typealias Pair = (Element, Element)
  
  // you can do zip(self, self.dropFirst), but this slightly
  // more complex version will work for single pass sequences as well
  func eachPair() -> some Sequence where Element == Pair  {
    var iterator = self.makeIterator()
    guard var previous = iterator.next() else {
      return AnySequence<Pair> { EmptyIterator<Pair>() }
    }
    
    return AnySequence { () -> AnyIterator<Pair> in
      AnyIterator {
        guard let next = iterator.next() else { return nil }
        defer { previous = next }
        return (previous, next)
      }
    }
  }
}

private struct EmptyIterator<Element>: IteratorProtocol {
  func next() -> Element? { nil }
}

Test.swift

func test() {
  let x = [1, 2, 3, 4]
  
  for pair in x.eachPair() {
    print(pair)
  }
}