[swift-evolution] [swift-users] for in? optionalCollection {

[Guillaume Lessard]

This could come for almost free after SE-0143 is implemented: an Optional of a Sequence could itself be made to conform to Sequence. It would cost no new syntax.

extension Optional: Sequence where Wrapped: Sequence {
  func makeIterator() -> AnyIterator<Wrapped.Iterator.Element> {
    switch self {
    case .some(let sequence):
      return AnyIterator(sequence.makeIterator())
    case .none:
      return AnyIterator { nil }
    }
  }
}

This would be more easily done than new syntax, surely.

Cheers,
Guillaume Lessard