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javaclojure

Apply for Java constructors

I have a vector of values, say [210 50 60] and I need to create Java object with it. For example I want to create Color:

(Color. 210 50 60)         ; standard way
(apply Color. [210 50 60]) ; hmm... I need something like this

Of course Color. is not a function and we cannot use apply on it. Is there an elegant way to solve this task or do I have to write it like this:

(let [[r g b] [210 50 60]]
  (Color. r g b))
Solution

  • If you dont mind paying the reflection cost I think https://stackoverflow.com/a/9172515/151650 is an elegant way. If you don't mind crazy macros: 

    (defn arity [c i]
  (let [args (map #(symbol (str "arg" %)) (range i))]
    `([~@args] (new ~c ~@args))))

(defmacro ->c [c]
   (let [cs (.getConstructors (resolve c))
         arities (set (map #(count (.getParameterTypes %)) cs))
         fn-arities (map #(arity c %) arities)]
     `(fn ~@fn-arities)))

(apply (->c java.awt.Color) 1 [2 3])