Look for a subarray in an array in Swift

isSubcollection.swift

extension Collection {
  /// True if `self` is a range within `collection`
  /// - Parameter collection: a `Collection` like `Array`
  /// - Returns: true or false
  ///
  /// Since this works with `Collection` it works with `Array`, `ArraySlic`, etc..
  func isSubcollection<U>(of collection:U) -> Bool
  where U:Collection, U.Element == Self.Element, Self.Element:Equatable
  {
    let (a,b) = (collection,self)
    for i in a.indices {
      var matches:Bool = true
      var i_runahead = i
      for j in b.indices {
        if b[j] != a[i_runahead] {
          matches = false
          break;
        }
        i_runahead = a.index(after: i_runahead)
      }
      if matches { return true }
    }
    return false

  }
}