Destructuring in function definition

[nidu]

Hello.

Is it recommended to destructure arguments in function definition or in let inside the function? The first approach affects readability though shortens the function. Any thoughts about this? E.g. compare

(defn distance-to-unit 
  [{:keys [scale units-per-pixel] :as viewer} dim value])

and

(defn distance-to-unit 
  [viewer dim value]
    (let [scale (:scale viewer)
          units-per-pixel (:units-per-pixel viewer)]))

[ToBeReplaced]

It depends. Make the function arguments self-documenting for the caller. If the argument is best understood as a viewer, the arglists should show that. I would use:

;;; Good: let binding inside function
(defn distance-to-unit
  [viewer dim value]
  (let [{:keys [scale units-per-pixel]} viewer]
    ...))

;;; Also good: Fix the arglists.
(defn distance-to-unit
  {:arglists '([viewer dim value])}
  [{:keys [scale units-per-pixel]} dim value]
    ...)

In the case of "options", I would do the destructuring in the function definition (and not alter the arglists) so that the keys show up in the function documentation automatically.

[nidu]

@ToBeReplaced i like the approach you provided with let. Definition is cleaner and you don't spread parameters definitions among multiple blocks.

Notice also that when you destructure parameters in function definition - you specify some kind of implicit protocol. You can say from it what keys should input arguments contain.

[kliph]

+1 for @ToBeReplaced suggestion for clear arguments.