So it would strike me that with-defaults-bad (below) is a fairly
straightforward way of using destructuring in Clojure yet it can't be
done, instead of passing the same map in that's being destrucured you
need a new "type" that has keys being the variable names instead of
keys being keywords... it would seem when using the :keys keyword
this shouldn't be necessary.
(defstruct params :x :y)
(def defaults (struct-map params :x 1 :y 2))
(defn no-defaults [{:keys [x y]}]
(list x y))
;since this is thing that's being destructed, I'd like to provide one
as default
; but this won't work because the :or expects the var names not the
keys
(defn with-defaults-bad [{:keys [x y] :or defaults}]
(list x y))
;note the absence of colons on the defaults matching the variables not
keys
; but now I can't use my nice structure as a default
(defn with-defaults-good [{:keys [x y] :or {x 1 y 2}}]
(list x y))
user> (no-defaults defaults)
(1 2)
user> (with-defaults-bad {:x 4 :y 5})
(4 5)
user> (with-defaults-bad {:x 4})
(4 nil)
user> (with-defaults-good {})
(1 2)
user> (with-defaults-good {:x 4})
(4 2)
minimally in the presence of the :keys feature in the paramaters it
would be nice if with-defaults-bad worked. although there are other
ways to work around this - this way just seems "cleaner"
also presumably the value of all defaults is evaluated at call time,
right?
Kevin
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