Consider the following code which attempts to redefine clojure/*out*:
(ns test
(:refer-clojure))
(def output System/out)
(def output-stream
(let [buffer (new java.io.ByteArrayOutputStream)]
(proxy [java.io.OutputStream] []
(flush []
(.append output (.toString buffer "UTF-8"))
(.reset buffer))
(write [x]
(when (>= (.size buffer) 32)
(.flush this))
(.write buffer x))
(write [x off len]
(.write buffer x off len)))))
(in-ns 'clojure)
(def *out* (new java.io.OutputStreamWriter test/output-stream "UTF-8"))
This works, but according to the the documentation of clojure/proxy it
seems that "If a method fn is not provided for a class method, the
superclass methd will be called." [1] However if I omit the second write
method in the proxy definition, I get the following error:
user=> (load-file "test.clj")
#=(var clojure/*out*)
user=> (prn "hello")
java.lang.IllegalArgumentException: Wrong number of args passed to: fn--2490$fn
(NO_SOURCE_FILE:0)
user=> (.printStackTrace *e)
java.lang.IllegalArgumentException: Wrong number of args passed to: fn--2490$fn
(NO_SOURCE_FILE:0)
at clojure.lang.Compiler.eval(Compiler.java:4122)
at clojure.lang.Repl.main(Repl.java:91)
Caused by: java.lang.IllegalArgumentException: Wrong number of args passed to:
fn--2490$fn
at clojure.lang.AFn.throwArity(AFn.java:460)
at clojure.lang.AFn.invoke(AFn.java:75)
at clojure.lang.Proxy__2499.write(Unknown Source)
at sun.nio.cs.StreamEncoder.writeBytes(StreamEncoder.java:202)
at sun.nio.cs.StreamEncoder.implFlushBuffer(StreamEncoder.java:272)
at sun.nio.cs.StreamEncoder.implFlush(StreamEncoder.java:276)
at sun.nio.cs.StreamEncoder.flush(StreamEncoder.java:122)
at java.io.OutputStreamWriter.flush(OutputStreamWriter.java:212)
at clojure.flush__906.invoke(boot.clj:1658)
at clojure.prn__909.doInvoke(boot.clj:1667)
at clojure.lang.RestFn.invoke(RestFn.java:413)
at user.eval__2503.invoke(Unknown Source)
at clojure.lang.Compiler.eval(Compiler.java:4111)
... 1 more
--------------------------------
[1] http://clojure.org/java_interop#toc20
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