Clojure evaluating string variable as a symbol, is this use of read-string okay?

Question

I can use memfn to create a clojure function that invokes a java function.

(macroexpand '(memfn startsWith prefix))
=> (fn* ([target2780 prefix] (. target2780 (startsWith prefix))))
((memfn startsWith prefix) "abc" "a")
=> true

memfn requires that the function name be a symbol. I'm wondering if I can write a macro to invoke an arbitrary method whose name is provided as a string. That is, I'd like to be able to invoke the following:

(def fn-name "startsWith")
=> #'user/fn-name
(macroexpand '(memfn' fn-name "prefix"))
=> (fn* ([target2780 prefix] (. target2780 (startsWith prefix))))
((memfn fn-name "prefix") "abc" "a")
=> true

The only way I can think to do this involves using read-string.

(defmacro memfn' [fn-name arg-name]
  `(memfn ~(read-string fn-name) ~arg-name))

Edit: A version using read-string and eval that actually works the way I want it to.

(defn memfn' [fn-name arg-name]
  (eval (read-string (str "(memfn " fn-name " " arg-name ")"))))

Am I missing a fundamental macro building tool to take the string that a symbol references and turn it into a literal without potentially executing code, as read-string might?

Thanks for any ideas!

Answer 1

There's no way to do this, with or without read-string. Your proposed solution doesn't work. The distinction you're really trying to make is not between string and symbol, but between runtime data and compile-time literals. Macros do not evaluate the arguments they receive, so even if fn-name is the name of a var whose value is "startsWith", memfn (or your memfn' macro) will only ever see fn-name.

Answer 2

If you are interested in calling java methods only then you can rely on java.lang.reflect.Method and its invoke method.

Something like this should work for parameterless methods and would not require a macro.

(defn memfn' [m]
  (fn [o] (.invoke (.getMethod (-> o .getClass) m nil) o nil)))

((memfn' "length") "clojure")
;=>7