common lisp 的访问器 GET

gistfile1.txt

语法
  get symbol indicator &optional default => value
  (setf (get symbol indicator &optional default) new-value)

参数和值
  symbol --- 一个 symbol
  indicator --- 一个 object
  default --- 一个 object, 默认为 nil
  value --- 如果指明的属性存在, 则这个 object的属性是value, 否则, 是默认的属性
  new-value --- 一个 object
  
描述
  get 获取 object 的属性

代码
  * (defvar man (gensym "MAN"))
  MAN
  
  * (get man 'wife)
  NIL
  
  * (setf (get man 'wife) "WIFE")
  "WIFE"
  
  * (get man 'wife)
  "WIFE"