小编gri*_*rit的帖子

我可以选择在defrecord的主体中直接实现协议,而不是使用extend-protocol/extend-type

(defprotocol Fly
  (fly [this]))

(defrecord Bird [name]
  Fly
  (fly [this] (format "%s flies" name)))

=>(fly (Bird. "crow"))
"crow flies"

如果我现在尝试覆盖Fly协议,我会收到错误

(extend-type Bird
  Fly
  (fly [this] (format "%s flies away (:name this)))

class user.Bird already directly implements interface user.Fly for protocol:#'user/Fly

另一方面,如果相反,我最初使用extend-type

(defrecord Dragon [color])

(extend-type Dragon
  Fly
  (fly [this] (format "%s dragon flies" (:color this))))

=>(fly (Dragon. "Red"))
"Red dragon flies"

然后我可以"覆盖"fly函数

(extend-type Dragon
  Fly
  (fly [this] (format "%s dragon flies away" (:color this))))

=>(fly (Dragon. "Blue"))
"Blue dragon …