How can I proxy a Java class with overloaded methods in Clojure?

Question

For example, given a Java class like:

public class Foo {
  public String bar(String x) {
    return "string " + x;
  }
  public String bar(Integer x) {
    return "integer " + x;
  }
}

How can I subclass Foo in Clojure and override only the bar(String) method but reuse the bar(Integer) from the original Foo class. Something like this (but this won't work):

(let [myFoo (proxy [Foo] [] 
              (bar [^String x] (str "my " x)))]
  (println "with string:  " (.bar myFoo "abc"))
  (println "with integer: " (.bar myFoo 10)))

This example will print:

with string:   my abc 
with integer:  my 10

but I would like to get the effect of:

with string:   my abc 
with integer:  integer 10

I don't have an answer, but your question spurred me to read "proxy_core.clj" which made me slightly smarter, so thanks! :) — Dave Ray
– Dave Ray, Commented May 19, 2011 at 12:17
I actually did the same. If anyone else is interested proxy_core.clj is here. — Jonathan Tran
– Jonathan Tran, Commented May 19, 2011 at 14:11

Jonathan Tran · Accepted Answer · 2011-05-19 05:37:37Z

4

I'm guessing this is not what you meant, but in the meantime, you can explicitly check the type of the argument and use proxy-super to call the original method on Foo.

(let [myFoo (proxy [Foo] [] 
              (bar [x]
                (if (instance? String x)
                  (str "my " x)
                  (proxy-super bar x))))]
  (println "with string:  " (.bar myFoo "abc"))
  (println "with integer: " (.bar myFoo 10)))

answered May 19, 2011 at 5:37

Jonathan Tran

15.3k9 gold badges64 silver badges67 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Alex Miller Over a year ago

I actually tried exactly this but was getting AbstractMethodError and other weird stuff (the real instance where I'm doing this is far more complicated of course). I'll have to try it again. Thanks!

kotarak Over a year ago

@alex-miller And you must be careful in case the Integer bar calls the back into the String bar. This won't work also with this approach. But @jonathan-tran is right: this is the only way to do this.

Collectives™ on Stack Overflow

How can I proxy a Java class with overloaded methods in Clojure?

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related