Clojure中的重新定义(脚本)

Question

我试图找到推迟var初始化的惯用方法(我真的打算成为不可变的).

(def foo nil)
...
(defn init []
  ; (def foo (some-function))
  ; (set! foo (some-function)))

我知道Rich Hickey说重新定义不是惯用的.是set!合适的吗？

Answer 1

我会用delay:

采用一个表达式体并产生一个Delay对象,该对象仅在第一次强制(使用force或deref/@)时调用正文,并将缓存结果并在所有后续强制调用中返回它.另见 - 实现？

用法示例:

(def foo (delay (init-foo))) ;; init-foo is not called until foo is deref'ed

(defn do-something []
  (let [f @foo] ;; init-foo is called the first time this line is executed,
                ;; and the result saved and re-used for each subsequent call.
    ...
    ))