Split string at camel case assurances, return array of substrings

split at cammel case.swift

func splitAtCamelCase(inString: String, var result:[String] = []) -> [String] {
        var previousLetter:String = ""
        var lastSplitIndex = 0
        if !inString.isEmpty { previousLetter = inString.characters.first.map{String($0)} ?? "" }
        for (index, currentLetter) in inString.characters.map({String($0)}).enumerate(){
            if previousLetter.isLowercase && currentLetter.isUppercase{
                let rangeWord = Range<Int>(start: lastSplitIndex, end: index)
                result.append(inString.substringWithRangeInt(rangeWord))
                lastSplitIndex = index
            }
            previousLetter = currentLetter
        }
        result.append(inString.substringFromIndexInt(lastSplitIndex))
        return result
    }