rangeOfString.swift

extension CollectionType where Generator.Element : Equatable {
  private func indexOf(from: Index)(_ e: Generator.Element) -> Index? {
    for i in from..<endIndex {
      if self[i] == e {
        return i
      }
    }
    return nil
  }
}

extension String.CharacterView {
  private func rangeOf(x: String.CharacterView, i: Index) -> Range<Index>? {
    guard let j = x.first.flatMap(indexOf(i)) else { return nil }
    var k = j
    for c in x {
      if k == endIndex { return nil }
      if c != self[k++] { return rangeOf(x, i: j.successor()) }
    }
    return j..<k
  }
}

extension String {
  public func rangeOf(x: String) -> Range<Index>? {
    return characters.rangeOf(x.characters, i: startIndex)
  }
}

import Foundation

let cs = Array("abcdefghij".characters)

func randString(length: Int) -> String {
  return String((0..<length).map { _ in
    cs[Int(arc4random_uniform(10))]
  })
}

!(0..<100).contains { _ in
  let long = randString(100)
  let shrt = randString(3)
  return long.rangeOf(shrt) != long.rangeOfString(shrt)
}