What's the difference between use and :use in the ns macro

0
votes

What's the difference between use and :use in the ns macro?

Docs says the following:

Use :use in the ns macro in preference to calling this directly
1
clojure

1 Answers

1
votes

It is a bit confusing.

In the ns form, you want to use the keyword version (:require ...) like:

(ns clj.core
  (:require [tupelo.core :as t] ))

You should consider this the "normal" way of doing things.

The other version, without the colon, is a function of the same name that can be called at the REPL in case you can't or don't want to use the ns form. This would look like:

> lein repl
user=> (require '[tupelo.core :as t] )
nil
user=> (t/append [1 2 3] 4)
[1 2 3 4]

Please note: For the repl/function version, you must also quote the vector containing the namespace specs. Notice that we did not quote the spec in the ns version using :require.

As an alternative, if you are already in the editor and just want to test something quick at the REPL, you can cut/paste the whole ns form from the top of your file into the REPL:

> lein repl
user=> (ns clj.core
  #_=>   (:require [tupelo.core :as t] ))
user=>

which is easier and less error-prone than typing the function-version by hand.

For a good overview please see the recent blog posting here: https://stuartsierra.com/2016/clojure-how-to-ns.html