'#' has been removed from Swift; 'greeting' already has an argument label
'#'已经从Swift语言中移除; 'greeting'已经有参数标签(即外部名字)了 - 这同时也能解释从第二个参数起不加参数标签会报错。例如:
sayHello("name", "Hello")
会报错
missing argument label 'greeting:' in call
