clojure.core/intern

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Type: function Added: Clojure 1.0 Examples: 4 Runnable: 0

([ns name] [ns name val])

Finds or creates a var named by the symbol name in the namespace ns (which can be a symbol or a namespace), setting its root binding to val if supplied. The namespace must exist. The var will adopt any metadata from the name symbol. Returns the var.

Examples

by Miles on 2010-09-07 . May have evaluation errors. ▶

(intern 'user 'x "Foobar") #'user/x x "Foobar"

by jungwookim on 2022-04-10 . May have evaluation errors. ▶

;; being able to define fn as a val (intern 'user 'sum (fn [a b c] (+ a b c))) #'user/sum (sum 1 2 3) 6

by jungwookim on 2022-04-10 . May have evaluation errors. ▶

;; you can defind defmethod as well by using intern. ;; firstly, define defmulti so that upper-case can convert string and keyword into upper-case, respectively. (defmulti upper-case [this] (type this)) ;; defmethods can be created as a var by clojure.core/intern (intern 'user 'upper-case (defmethod upper-case java.lang.String [this] (clojure.string/upper-case this))) (intern 'user 'upper-case (defmethod upper-case clojure.lang.Keyword [this] (-> this name clojure.string/upper-case keyword))) (upper-case "abc") "ABC" (upper-case :abc) :ABC

by tomdl89 on 2023-12-03 . May have evaluation errors. ▶

;; `intern` can be used to allow defining in other namespaces… (create-ns 'other-ns) #namespace[other-ns] (intern 'other-ns 'foo 42) #'other-ns/foo (inc other-ns/foo) 43

Note by phreed

"The Namespace system maintains global maps of symbols to Var objects (see Namespaces). If a def expression does not find an interned entry in the current namespace for the symbol being def-ed, it creates one, otherwise it uses the existing Var. This find-or-create process is called interning. This means that, unless they have been unmap-ed, Var objects are stable references and need not be looked up every time. It also means that namespaces constitute a global environment in which, as described in Evaluation, the compiler attempts to resolve all free symbols as Vars.

"The var special form or the #' reader macro (see Reader) can be used to get an interned Var object instead of its current value."

-- [https://clojure.org/reference/vars]

See also

• clojure.core/alter-var-root (2)
• clojure.core/ns-unmap
• clojure.core/create-ns (0)

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