Swift 2 function to test if a string is a palindrome

Palindrome.swift

func isPalindrome(string:String) -> Bool {
    if string.isEmpty || string.characters.count == 1 {
        return true
    }
    
    var fromStart = string.startIndex
    var fromEnd = string.endIndex.predecessor()
    
    while fromStart != fromEnd {
        if string[fromStart] != string[fromEnd] {
            return false
        }
        
        if fromStart.successor() == fromEnd { // if even length string
            return string[fromStart] == string[fromEnd]
        }
        
        fromStart = fromStart.successor()
        fromEnd = fromEnd.predecessor()
    }
    
    return true
}