firstLiteralMatch.swift

extension Collection where Element: Hashable {
  /// Returns the first matching element in `needles`, along with its index.
  func firstLiteralMatch<C: Collection>(from needles: C) -> (C.Element, Index)?
    where C.Element: Collection, C.Element.Element == Element
  {
    let prefixes = Dictionary(grouping: needles, by: { $0.first! })
    for i in indices {
      if let possibleMatches = prefixes[self[i]] {
        if let match = possibleMatches.first(where: { self[i...].starts(with: $0) }) {
          return (match, i)
        }
      }
    }
    return nil
  }
}

let text = """
  Lorem ipsum dolor sit amet, consectetur adipiscing elit. \
  Nullam a imperdiet magna. Quisque quis libero non risus \
  commodo efficitur. Sed lorem urna, scelerisque sit \
  amet porta eget, efficitur at libero. Ut a viverra augue.
  """

text.firstLiteralMatch(from: ["sit", "elit", "libero"])
// ("sit", ...)