使用哈希映射中的命名参数调用Clojure函数

Question

I would like to be able to pass named parameters to a function from a hash map. Let's say I have a function like this:

(defn foo [a & {:keys [b]}] (println a b))

I want to be able to call it with parameters coming from a map. I know I can do it like this:

(apply foo 1 (mapcat identity {:b 2}))

But surely there must be a more idiomatic and less clunky way to do this, right?

Answer 1

Nope, there is no other less clunky way. It would be better to make your foo to take a hash-map as parameter and pattern match on it for keys:

(defn foo [a {:keys [b]}] (println a b))
(foo 1 {:b 2})

Answer 2

No, there isn't. But you may use concat directly instead of doing it through mapcat :

(apply foo 1 (apply concat {:b 2}))

You may also use ->> macro to make it clearer (though not shorter):

(->> {:b 2}
     (apply concat)
     (apply foo 1))