gistfile1.clj

(defn proxy-meta
  "Returns an anonymous class instance, constructed with the file on the path
indicated by `infile', annotated with metadata indicating the filename used to
construct the instance. Optional `moremeta' is a single map containing any
additional metadata to add to the instance."
  [infile & moremeta]
  (let [metadata (merge {:filename infile} (first moremeta))]
    (proxy [PdfReader clojure.lang.IObj] [infile]
      (withMeta [new-meta] (merge metadata new-meta))
      (meta [] metadata))))

(defn with-proxy-meta
  "Returns a new copy of `obj' with metadata updated as indicated by
`metadata'.

Usage: `(with-proxy-meta (pdf<- path-to-pdf) {:foo 100})'
"
  [obj metadata]
  (let [key :filename
        new-meta (merge (meta obj) metadata)]
    (proxy-meta (key new-meta) (dissoc new-meta key))))