gistfile1.txt

// This should have worked. It doesn't work.
// Out of range error because the String.Index is set with regard to the smallest string at match

//extension String {
//
//   func findIndexOf(substring : String) -> String.Index? {
//        if countElements(self) < countElements(substring) {return nil}
//        if countElements(substring) == 0 {return nil}
//        if self.hasPrefix(substring) {return self.startIndex}
//        if let recursionResults = dropFirst(self).findIndexOf(substring) {
//            return recursionResults.successor()
//        } else {
//            return nil
//        }
//   }
//}
 
extension String {
 
   func indexOfSubstring(substring : String) -> Int? {
        if countElements(self) < countElements(substring) {return nil}
        if countElements(substring) == 0 {return nil}
        if self.hasPrefix(substring) {return 0}
        if let recursionResults = dropFirst(self).indexOfSubstring(substring) {
            return recursionResults + 1
        } else {
            return nil
        }
   }
 
   func findIndexOf(substring : String) -> String.Index? {
        if let result = self.indexOfSubstring(substring) {
            return advance(self.startIndex, result)
        } else {
            return nil
        }
    }
}
 
var x = "Hello, World"
println(x.findIndexOf("World"))
let clarus = "🐶🐮"
println(clarus.findIndexOf("🐮"))
 
println(clarus.startIndex) // prints 0
println(advance(clarus.startIndex, 1)) // prints 2