(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?
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