How to call a static method on an incoming class-pointer in Clojure? [duplicate]

Question

I wanted to get the bit size of bounded primitives in Clojure. These can be found with

(java.lang.Integer/SIZE)
=>32

or the equal, less sweet

(. java.lang.Integer SIZE)
=> 32

(I use java.lang.*-names just for clarity in these examples, they can be omitted)

Of course I wanted to parametrize the call, like

(def integer-class java.lang.Integer)

(. integer-class SIZE)
CompilerException java.lang.RuntimeException: Unable to resolve symbol: intger-class in this context, compiling:(/private/var/folders/yt/g82v06jn63qc5273rx4zjx440000gn/T/form-init4887476821027963248.clj:1:1)

The number of bounded primitives are limited in Java, which makes this exercise a bit academic, but the questions would be:

How do I (dynamically) call a static method in a class given as a var?

Community · Accepted Answer · 2017-05-23 12:03:44Z

1

As ponzao says, the Clojure vars and Java static methods has an answer with a macro jcall that solves the problem.

(defmacro jcall [obj & args]
  (let [ref (if (and (symbol? obj) 
                  (instance? Class (eval obj)))
              (eval obj)
              obj) ]
    `(. ~ref ~@args)))

(jcall java.lang.Integer SIZE) => 32!

Thanks.

edited May 23, 2017 at 12:03

CommunityBot

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answered Jan 2, 2014 at 14:31

claj

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