爲什麼add-hook允許`hook'無效？

Question

從C-H添加F-鉤：

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. 

，並從代碼：

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

這是什麼好處？我認爲這是有用的，否則它不會在那裏......我只是想不出它的好用處......

Answer 1

它允許你在定義它們的包之前設置鉤子變量加載。