Variadic Zip Function in Swift

Question

Variadic Zip Function

Swift 4.1, Xcode 9.4

I have been using Apple\'s native zip(_:_:) recently and I ran into a situation whereby I needed

Answer 1

You need all the functions but you don't need multiple ZipSequence types.

@inlinable public func zip(
  _ sequence0: Sequence0, _ sequence1: Sequence1, _ sequence2: Sequence2
) -> AnySequence<(Sequence0.Element, Sequence1.Element, Sequence2.Element)> {
  .init(
    sequence(
      state: (
        sequence0.makeIterator(), sequence1.makeIterator(), sequence2.makeIterator()
      )
    ) {
      .init(
        ($0.0.next(), $0.1.next(), $0.2.next())
      )
    }
  )
}

@inlinable public func zip<
  Sequence0: Sequence, Sequence1: Sequence, Sequence2: Sequence, Sequence3: Sequence
>(
  _ sequence0: Sequence0, _ sequence1: Sequence1, _ sequence2: Sequence2, _ sequence3: Sequence3
) -> AnySequence<(Sequence0.Element, Sequence1.Element, Sequence2.Element, Sequence3.Element)> {
  .init(
    sequence(
      state: (
        sequence0.makeIterator(), sequence1.makeIterator(), sequence2.makeIterator(), sequence3.makeIterator()
      )
    ) {
      .init(
        ($0.0.next(), $0.1.next(), $0.2.next(), $0.3.next())
      )
    }
  )
}

public extension Optional {
  /// Exchange three optionals for a single optional tuple.
  /// - Returns: `nil` if any tuple element is `nil`.
  init(_ optionals: (Wrapped0?, Wrapped1?, Wrapped2?))
  where Wrapped == (Wrapped0, Wrapped1, Wrapped2) {
    switch optionals {
    case let (wrapped0?, wrapped1?, wrapped2?):
      self = (wrapped0, wrapped1, wrapped2)
    default:
      self = nil
    }
  }

  /// Exchange four optionals for a single optional tuple.
  /// - Returns: `nil` if any tuple element is `nil`.
  init(_ optionals: (Wrapped0?, Wrapped1?, Wrapped2?, Wrapped3?))
  where Wrapped == (Wrapped0, Wrapped1, Wrapped2, Wrapped3) {
    switch optionals {
    case let (wrapped0?, wrapped1?, wrapped2?, wrapped3?):
      self = (wrapped0, wrapped1, wrapped2, wrapped3)
    default:
      self = nil
    }
  }
}