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clojure 2026-06-01
I am aware of the documented behavior of
(defn configure [val & {:keys [debug verbose]
:or {debug false, verbose false}
:as opts}]
(println "val =" val " debug =" debug " verbose =" verbose " opts =" opts))opts to nil when called via (configure "xxx)
Nevertheless I often would want in this situation, that opts get bound to the default, so {debug false, verbose false}
Is there a way to get this ?
p-himik 2026-06-01T17:11:15.591069Z
Nothing that's built into Clojure. You gotta do some manual processing of opts to merge the default values in.
Something like
(defn configure [val & {:as opts}]
(let [opts (merge-with (fn [v _] v) opts {:debug false :verbose false})]
...))
Alex Miller (Clojure team) 2026-06-01T17:24:09.487299Z
usually I just merge into a defaults map, then destructure
Alex Miller (Clojure team) 2026-06-01T17:27:29.710179Z
(defn configure [val & opts]
(let [{:keys [debug verbose]} (merge {:debug false, :verbose false} opts)]
(println "val =" val " debug =" debug " verbose =" verbose " opts =" opts)))
(configure 1)
val = 1 debug = false verbose = false opts = nilAlex Miller (Clojure team) 2026-06-01T17:28:49.576719Z
can explicitly bind the "opts with defaults" too if you want to break it apart
Alex Miller (Clojure team) 2026-06-01T17:31:14.984299Z
and I don't think it's possible to change what :or does now without breaking lots of code. but perhaps something could be added that did this like :defaults, that just did the merge above for you
Alex Miller (Clojure team) 2026-06-01T17:32:25.122529Z
:and instead of :or :)
Alex Miller (Clojure team) 2026-06-01T17:46:36.335289Z
I logged a jira https://clojure.atlassian.net/browse/CLJ-2957 for enhancement to keep track of this, feel free to vote on the ask above
➕ 3
Maybe one of the biggest advantage of an "extended" support of this inside the function signature itself, would be to "auto-document" such a 'default', as most IDEs show "full function signatures":
Alex Miller (Clojure team) 2026-06-01T18:57:03.766179Z
yes
Alex Miller (Clojure team) 2026-06-01T18:57:29.808869Z
may have interesting entanglements with the upcoming required keys enhancements
Required keys enhancements?
Dave Liepmann 2026-06-02T07:56:52.855379Z
@jason.bullers last clojure dev call dropped some info (caveat, everything is still being designed) about adding something like :keys! destructuring that requires the keys specified (e.g. throws IllegalArgumentException if they are not present). See https://clojurians.slack.com/archives/C06E3HYPR/p1779828764865859
Cool, I'll check that out. Hadn't heard about it before. Thanks!