为什么add-hook允许`hook'无效？

Question

从C-H添加F-钩：

HOOK should be a symbol, and FUNCTION may be any valid function. If 
HOOK is void, it is first set to nil. If HOOK's value is a single 
function, it is changed to a list of functions. 

，并从代码：

(defun add-hook (hook function &optional append local) 
    ... 
    (or (boundp hook) (set hook nil)) 
    (or (default-boundp hook) (set-default hook nil)) 
    ... 

这是什么好处？我认为这是有用的，否则它不会在那里......我只是想不出它的好用处......

Answer 1

它允许你在定义它们的包之前设置钩子变量加载。