difference between use and require

user_1586 0
Viewed 36157

Can anyone explain the difference between use and require, both when used directly and as :use and :require in the ns macro?

clojure
4 Answers

require loads libs (that aren't already loaded), use does the same plus it refers to their namespaces with clojure.core/refer (so you also get the possibility of using :exclude etc like with clojure.core/refer). Both are recommended for use in ns rather than directly.

user_958100

Use sure does make it easier by not requiring you to spell out the namespace every time you want to call a function though it can also make a mess of things by creating namespace conflicts. A good middle ground between "use" and "require" is to only 'use' the functions from a namespace that you actually use.

for instance: 

 (use '[clojure-contrib.duck-streams :only (writer reader)])
or even better, specify it at the top of the file in the namespace definition:

(ns com.me.project
   (:use [clojure.contrib.test-is :only (deftest is run-tests)]))
user_908010

As has been mentioned the big difference is that with (require 'foo), you then refer to names in the lib's namespace like so: (foo/bar ...) if you do (use 'foo) then they are now in your current namespace (whatever that may be and provided there are no conflicts) and you can call them like (bar ...).

twopoint718_4488580
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