CODEWITHSUNDEEP
syntaxclojureclojurescriptom
FeifanZ
FeifanZ

Reputation: 16316

Clojure — Meaning of pound symbol?

In the Om Next Quick Start, they use #js and #uuid. What does the pound symbol here mean?

Link: https://github.com/omcljs/om/wiki/Quick-Start-(om.next)#components-with-queries--mutations

Snippets:

#js:

(defui Counter
  static om/IQuery
  (query [this]
    [:count])
  Object
  (render [this]
    (let [{:keys [count]} (om/props this)]
      (dom/div nil
        (dom/span nil (str "Count: " count))
        (dom/button
          #js {:onClick
               (fn [e] (om/transact! this '[(increment)]))}
          "Click me!")))))

#uuid:

(om/from-history reconciler
  #uuid "9e7160a0-89cc-4482-aba1-7b894a1c54b4")

Upvotes: 5

Views: 1256

Answers (1)

a3.14_Infinity
a3.14_Infinity

Reputation: 5861

Commonly found in EDN and ClojureScript this use of # is called the tagged literal. Look at this example,

user=> (java.util.Date.)
#inst "2014-05-19T19:12:37.925-00:00"

When we create a new date it is represented as a tagged literal, or in this case a tagged string. We can use Clojures read-string to read this back (or use it directly)

user=> (type #inst "2014-05-19T19:12:37.925-00:00")
java.util.Date
(read-string "#inst \"2014-05-19T19:12:37.925-00:00\"")
#inst "2014-05-19T19:12:37.925-00:00"
user=> (type (read-string "#inst \"2014-05-19T19:12:37.925-00:00\""))
java.util.Date

A tagged literal tells the reader how to parse the literal value. Other common uses include #uuid for generating UUIDs and in the ClojureScript world an extremely common use of tagged literals is #js which can be used to convert ClojureScript data structures into JavaScript structures directly.

Courtesy: The Weird and Wonderful Characters of Clojure

Upvotes: 6

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