multiply/divide with BigDecimal

[jgeraerts]

This clojure wrapper uses type hints to make the multiplier explicitly a double, probably to avoid reflection warnings. However the joda money java library also has a multiplied by method taking a BigDecimal as multiplier. Currently this cannot be used from this library.

I'm willing to add this functionality, but it is unclear to me how to proceed in a idiomatic way:

• add a second methodname implying the type, e.g. multiply-by-bigdecimal or
• add a conditional check on the type in the current multiply method, adding typehints in the dispatch to the joda time library itself or
• replace the multiply function with a multimethod dispatching on type (slight variant of the above) or
• remove the typehints completely (like minus/plus)

[michaelklishin]

Joda Time has "type hints" (signatures) by definition ;) You can use a single function that then dispatches to a protocol (and not a multi-method), where each implementation has a type hint.

[jgeraerts]

And then swap the arguments in the Protocol function so i can dispatch on the multiplier type?

[michaelklishin]

Simply delegate to the protocol function. It should avoid reflection (which is the point of type hints).

On 1 abr 2016, at 12:38, Jo Geraerts notifications@github.com wrote:

And then swap the arguments in the Protocol function so i can dispatch on the multiplier type?

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[jgeraerts]

So for example your current function multiply

(defn ^Money multiply
  ([^Money money ^double multiplier]
     (.multipliedBy money multiplier (cnv/to-rounding-mode nil)))
  ([^Money money ^double multiplier rounding-mode]
     (.multipliedBy money multiplier (cnv/to-rounding-mode rounding-mode))))

would become

(defprotocol AmountOps
  (op-multiply [multiplier money rounding-mode]))

(extend-protocol AmountOps
  double
  (op-multiply [multiplier ^Money money rounding-mode]
    (.multipliedBy money multiplier rounding-mode))
  java.math.BigDecimal
  (op-multiply [multiplier ^Money money rounding-mode]
    (.multipliedBy money multiplier rounding-mode)))

(defn ^Money multiply
  ([^Money money ^double multiplier]
     (op-multiply multiplier money (cnv/to-rounding-mode nil)))
  ([^Money money ^double multiplier rounding-mode]
     (op-multiply multiplier money (cnv/to-rounding-mode rounding-mode))))

And then ofcourse similar for the other operations. The only thing i feel dirty about is the parameter order in the protocol, especially for op-minus it gets counter intuitive.

[michaelklishin]

That actually might be nicer than what I had in mind. We still need to drop the type hint from multiply.

[jgeraerts]

alright, i'll work it out.