为什么不在此功能中键入提示提高性能？

Here is the code:

这是代码:

(defn first-char-of-either [^String a  ^String b]
  (.substring (or a b) 0 1))
(defn first-char-of-either1 [^String a  ^String b]
  (.substring ^String (or a b) 0 1))
(time (dorun (repeatedly 1000000 #(first-char-of-either  nil "abcde"))))
(time (dorun (repeatedly 1000000 #(first-char-of-either1 nil "abcde"))))
(defn first-char-of