emacs - 为什么 add-hook 允许 `hook' 无效？

Question

来自 C-h f 添加钩子(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.

来自代码:

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

这有什么用？我认为它在某种程度上是有用的，否则它不会存在......我只是想不出它有什么好的用途......

Answer 1

它允许您在加载定义它们的包之前设置钩子(Hook)变量。