Question

什么是(class =)和(type =)的区别？
谢谢！

Answer 1

使用REPL

=> (source type)
(defn type 
  "Returns the :type metadata of x, or its Class if none"
  {:added "1.0"
   :static true}
  [x]
  (or (get (meta x) :type) (class x)))
nil
=> (source class)
(defn class
  "Returns the Class of x"
  {:added "1.0"
   :static true}
  ^Class [^Object x] (if (nil? x) x (. x (getClass))))
nil

Comments

谢谢！
你能写一个例子，其中(class Something)和(type Something)的输出值不相等吗？

:-)

---

嗨 Eugene。这可能有所帮助

    (def sym (with-meta 'foo {:type :foo-type-tag}))
    (class sym)
    ;;=> clojure.lang.Symbol
    (type sym)
    ;;=> :foo-type-tag

---

这里还有一个例子： https://docs.clojure.org/clojure.core/type#example-542692cfc026201cdc326e2d

以及这里扩展上述 `sym` 例子，看看 `type` 可能为何用途

    => (defmethod print-method :foo-type-tag [v w] (.write w (str "Custom print:" v)))
    #object[clojure.lang.MultiFn 0x3a4ba480 "clojure.lang.MultiFn@3a4ba480"]
    => (println sym)
    Custom print:foo
    nil