clojure.core/*ns*

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Type: var Added: Clojure 1.0 Examples: 3 Runnable: 0

()

A clojure.lang.Namespace object representing the current namespace.

Examples

by boxie on 2010-11-06 . May have evaluation errors. ▶

*ns* #<Namespace user>

by rafmagana on 2014-07-23 . May have evaluation errors. ▶

(ns foo.bar) nil *ns* #<Namespace foo.bar>

by Artiavis on 2017-06-18 . May have evaluation errors. ▶

;; A (rare) trap which can happen is attempting to dynamically call `in-ns`, due to how ;; `*ns*` is really an instance of `clojure.lang.Var` with a root binding. (ns my.namespace) nil *ns* #<Namespace my.namespace> ;; This will *only* work in the REPL (or REPL-like environments)!! ;; Tools like Boot and Lein may or may not provide this (read the manual/code) (defn swap-ns! [ns-name] (in-ns ns-name)) #'my.namespace/swap-ns! (swap-ns! 'other.ns) #namespace[other.ns] ;; Later, at runtime... ;; Throws IllegalStateException("Can't change/establish root binding of: *ns* with set") ;; Remember, *ns* is a root var and in-ns calls set!, which only works after ;; someone somewhere calls the binding macro (or Java equivalent) (defn -main [& args] (println *ns*) (swap-ns! 'arbitrary-namespace)) ;; prints #namespace[clojure.core] and then will crash

Note by gstamp

A trap I fell into was that ns seems to get assigned to clojure.core when run as a "gen-class" compiled class.

Note by Artiavis

To clarify the above point, see my example above. Although within Lein/Boot/REPL/Compiler contexts, *ns* is thread-local due to the use of the binding machinery, and so in-ns works in those situtations, *ns* has a root of clojure.core. That means that, at runtime, you cannot call in-ns within functions until you've first called binding. (This could be relevant for e.g. eval calls.)

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