'#' has been removed from Swift; 'greeting' already has an argument label
'#'已經從Swift語言中移除; 'greeting'已經有參數標簽(即外部名字)了 - 這同時也能解釋從第二個參數起不加參數標簽會報錯。例如:
sayHello("name", "Hello")
會報錯
missing argument label 'greeting:' in call
