clojure - 你能扩展一个类型/记录来实现 Clojure 中的 str 函数吗？

Question

我有一个用 defrecord 定义的 Book 类型，以及一个将它转换成字符串的函数:

(defrecord Book [title author])
(defn book->string [book] (str (:title book) " by " (:author book))) 

(book->string (->Book "Foo" "Bar"))  ;; "Foo by Bar"

是否可以扩展记录以便我可以调用 (str (->Book "Foo""Bar"))？

Answer 1

你不必扩展任何东西，只需覆盖toString方法:

(defrecord Book [title author]
  Object
  (toString [_] (str title " by " author)))

测试:

(str (->Book "Foo" "Bar"))
=> "Foo by Bar"