clojure - 在 defn 宏中，函数名称前以插入符号开头的参数是什么意思？

Question

在函数定义中：

(defn ^boolean =
  ;;other arities omitted...
  ([x y]
    (if (nil? x)
      (nil? y)
      (or (identical? x y)
        ^boolean (-equiv x y))))

函数定义中的^boolean部分是什么意思？它只是扩展元数据并表示返回类型，还是有更深层次的含义？换句话说，它是否比简单地使代码更具自我描述性更有价值？

Answer 1

It is a type hint. See

https://www.safaribooksonline.com/library/view/clojure-programming/9781449310387/ch09s05.html

http://clojure-doc.org/articles/language/functions.html

or your favorite book. PLEASE NOTE: the compiler does not enforce that the actual type matches the type hint! Example w/o type hint:

(defn go []
  "banana" )
(println (go))
;=> banana

(defn ^long go []
  "banana" )
(println (go))
;=> Exception in thread "main" java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Number,