Minus infix for Swift strings

minus

@infix func - (left: String, right: String) -> String {
    var finalString = left
    
    if left.hasSuffix(right) {
        // the workaround to the compiler error is to cast the String to NSString before the substringToIndex method
        var index = countElements(left) - countElements(right)
        finalString = (left as NSString).substringToIndex(index)
    }

    return finalString
}

"Apple Computers" - " Computers"