Can anyone explain the difference between "use" and "require", both when used directly and as :use and :require in the ns macro?
+11
A:
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.
Alex Martelli
2009-05-16 09:24:49
If I require lib foo, then to use bar in foo, I'd have to write foo/bar every time, right? Why would you want to load a lib in ns but then not refer it into the ns? I guess you might be worried about collisions, and you don't want to bother having to reconcile them, right?
Jegschemesch
2009-05-16 12:14:47
not having to reconcile collisions is a good point, and more generally there's a programming style which says "namespaces are a honking great idea, we should have more of them" (from "The Zen of Python") -- so e.g. that style recommends not using "using namespace foo;" in C++, so that readers and maintainers of the code won't have to worry "where does this bar come from" but see a more explicit foo::bar instead. require (vs use) supports this "explicit namespaces" style.
Alex Martelli
2009-05-18 04:20:48
+4
A:
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
2009-06-18 04:42:10