Herwig Hochleitner schreef op 2015-07-08 05:20:
2015-07-07 15:04 GMT+02:00 Jo Geraerts <j...@umask.net [1]>:
* multiply(long x)
* multiply(double x)
* multiply(Number x)
In clojure i want to do something like
(defn multiply[^MonetaryAmount amount multiplicant]
(.multiply amount multiplicant))
Function parameters in Clojure, are generally passed as a
java.lang.Object, so numbers are boxed by default.
Clojure does have infrastructure to pass primitive numbers, see
invokePrim
here:
https://github.com/clojure/clojure/blob/master/src/jvm/clojure/lang/IFn.java#L97
[2] see also http://clojure.org/java_interop#Java [3] Interop-Support
for Java Primitives
however, this requires a specific type hint on the multiply fn, so
normally that means separate multiply-double and multiply-long fns.
The way I would do it: Define multiply as a function calling
(.multiply amount ^Number x), for higher order usage, and then add an
:inline function to its metadata, which returns `(.multiply ~amount
~x).
That acts as a compiler macro, which inlines the call to .multiply,
that way, its parameter type can be assigned via local type
inferrence
(which clojure does).
See http://www.bytopia.org/2014/07/07/inline-functions-in-clojure/#sec-3
[4]
Beware, that inline functions aren't public API and subject to
change.
This is enlightening. I found such constructs in clojure's core.clj
cause there similar things should happen for certain functions, but i
couldn't fully grasp what was going on. In core.clj also quite some
dispatching happens to clojure.lang.RT which i figured was part of the
:inline setup.
Thank you for the explanation.
Kr,
Jo
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