为什么add-hook允许`hook'无效？

Question

来自 C-h f add-hook ：

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.

并从代码中获取：

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

这有什么好处？我认为它在某种程度上是有用的，否则它就不会存在......我只是想不出它的好用......

Answer 1

它允许您在加载定义它们的包之前设置钩子变量。