(import 'java.io.DataOutputStream)
(import 'java.io.ByteArrayOutputStream)
(defn- ->bytes
"Convert a Java primitive to its byte representation."
[write v]
(let [output-stream (ByteArrayOutputStream.)
data-output (DataOutputStream. output-stream)]
(write data-output v)
(seq (.toByteArray output-stream))))
(defn int->bytes [n]
(->bytes
#(.writeInt ^DataOutputStream %1 %2)
n))
(defn int->bytes-ref [n]
(->bytes
#(.writeInt %1 %2)
n))
user=> (int->bytes 5)
(0 0 0 5)
user=> (int->bytes-ref 5)
(0 0 0 5)
user=> (int->bytes (inc Integer/MAX_VALUE))
IllegalArgumentException Value out of range for int: 2147483648 clojure.lang.RT.intCast (RT.java:1115)
user=> (int->bytes-ref (inc Integer/MAX_VALUE))
(-128 0 0 0)
So it looks like type-hinting the DataOutputStream results in bytecode calling RT.intCast, which throws because the value is too large. In the reflective case, we locate the method writeInt at runtime, and then do not call RT.intCast, but instead allow the long to be downcast without bounds checking.
It seems like we should be calling RT.intCast in both cases?
