I have a Clojure program that I build as a JAR file using Maven.
Embedded in the JAR Manifest is a build-version number, including the
build timestamp.

I can easily read this at runtime from the JAR Manifest using the
following code:

(defn set-version
  "Set the version variable to the build number."
  []
  (def version
    (-> (str "jar:" (-> my.ns.name (.getProtectionDomain)
                                   (.getCodeSource)
                                   (.getLocation))
                    "!/META-INF/MANIFEST.MF")
      (URL.)
      (.openStream)
      (Manifest.)
      (.. getMainAttributes)
      (.getValue "Build-number"))))
but I've been told that it is bad karma to use def inside defn.

What is the Clojure-idiomatic way to set a constant at runtime? I
obviously do not have the build-version information to embed in my
code as a def, but I would like it set once (and for all) from the
main function when the program starts. It should then be available as
a def to the rest of the running code.

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