plus.clj

(definterface IMixedAddition
  (plus [^Long x ^Double y])
  (plus [^Double x ^Long y]))

(deftype MixedAdditionImpl []
  IMixedAddition
  (plus [this ^Long x ^Double y]
    "foo")
  (plus [this ^Double x ^Long y]
    "bar"))

(def dummy (MixedAdditionImpl.))

(time (dotimes [_ 1e6]
        (.plus dummy (long 1) (double 1))))

;; Reflection warning, NO_SOURCE_FILE:1 - call to plus can't be resolved.
;; "Elapsed time: 1560.983138 msecs"

(defmulti multiplus (fn [l r] [(type l) (type r)]))

(defmethod multiplus [Long Double]
  [l r]
  "foo")

(defmethod multiplus [Double Long]
  [l r]
  "bar")

(time (dotimes [_ 1e6]
        (multiplus (long 1) (double 1))))

;; "Elapsed time: 781.060692 msecs"