Clojure强制性关键字参数(Clojure Mandatory keyword argument)

Clojure强制性关键字参数(Clojure Mandatory keyword argument)

我有这样的功能：

(defn foo [{a :keya b :keyb}] (list a b))

我这样称呼它：

(foo {:keya "hi"}) ; Returns ("hi" nil)

如果我没有给出keyb关键字参数，那么它就是零。 有没有办法确保它为它抛出异常，而不是将它作为零。

（我知道我可以手动检查并抛出一个异常，但是是否有任何特殊的选项来强制约束。）

I have a function like this:

(defn foo [{a :keya b :keyb}] (list a b))

And i'm calling it like this:

(foo {:keya "hi"}) ; Returns ("hi" nil)

If I don't give keyb keyword argument, it takes nil for that. Is there a way to ensure that it throws exception for it instead of taking it as nil.

( I know that I can manually check and throw an exception, but is there any special option which enforces the constraints.)

最满意答案

您可以使用前提条件（ http://clojure.org/special_forms#toc9 ）来声明密钥存在：

(defn foo [{a :keya b :keyb}] {:pre [(not (nil? b))]} (list a b))

当密钥为零时，这将引发一个AssertionError。

You can use a precondition (http://clojure.org/special_forms#toc9) to assert the key is present:

(defn foo [{a :keya b :keyb}] {:pre [(not (nil? b))]} (list a b))

This will throw an AssertionError when the key is nil.