failed to work on xCode 7 stand alone swift file

[Fred-J]

On xCode 7.1.1, open a stand alone .swift file not in a project.
typing
let replacement = (fullPath as NSString).
looking for
stringByReplacingOccurrencesOfString
but it is no where to be found.
desired output is:
let replacement = (fullPath as NSString).stringByReplacingOccurrencesOfString(oldName, withString: newName)