Basic question: what's the difference between "require as" and "use as"?

[Ritchie Cai]

For example:

(:require [clojure.java.io :as io]) 

vs

(:use [clojure.java.io :as io])

In both cases, we can end up using it with "(io/<function name> ... )". Is there a difference at all?

Thanks

Ritchie

[Sean Corfield]

Yes, (:use [clojure.java.io :as io]) is equivalent to (:require [clojure.java.io :as io :refer :all]) so it refers in all of the symbols from that namespace directly into your namespace (i.e., they can be referenced even without the io/ prefix).

Sean Corfield -- (904) 302-SEAN
An Architect's View -- http://corfield.org/

"Perfection is the enemy of the good."
-- Gustave Flaubert, French realist novelist (1821-1880)

[Ritchie Cai]

You mean (:use [clojure.java.io]) is equivalent to (:require [clojure.java.io :as io :refer :all])?

Ritchie

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[Sean Corfield]

On Jun 22, 2015, at 2:22 PM, Ritchie Cai <ritch...@gmail.com> wrote:
> You mean (:use [clojure.java.io]) is equivalent to (:require [clojure.java.io :as io :refer :all])?

Not quite, (:use [clojure.java.io]) is equivalent to (:require [clojure.java.io :refer :all])

[Ritchie Cai]

Ok, so require without :refer will default to :refer :all?

[Sean Corfield]

On Jun 22, 2015, at 2:39 PM, Ritchie Cai <ritch...@gmail.com> wrote:
> Ok, so require without :refer will default to :refer :all?

No.

>> (:use [clojure.java.io]) is equivalent to (:require [clojure.java.io :refer :all])

There’s no :as here. :use is like :require :refer :all.

>> (:use [clojure.java.io :as io]) is equivalent to (:require [clojure.java.io :as io :refer :all])

There’s an :as in both here. :use :as is like :require :as :refer :all

Both :use and :refer :all (in :require) are discouraged because they pollute your namespace with every symbol from the used/required namespace.

There’s not much point in specifying an alias (with :as) for :use or :require :refer :all since those bring in every symbol directly anyway.

[Ritchie Cai]

Ah, I see. I thought “use :as” will not intern all the symbols into current namespace, apparently that’s not the case.
Thanks for clearing this up.

Ritchie

[Gary Verhaegen]

Unless you have a very compelling reason, just don't use use. It's mostly a historical accident that's kept there for backwards compatibility.

And try to avoid :refer :all if possible. There are legitimate use-cases for it, but outside the REPL they are pretty rare.

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[Ritchie Cai]

I always have (:use clojure.core) in a new namespace. Is that necessary or is clojure.core is automatically interned when a new namespace is created?

[Fluid Dynamics]

On Tuesday, June 23, 2015 at 10:40:25 AM UTC-4, Ritchie Cai wrote:

I always have (:use clojure.core) in a new namespace. Is that necessary or is clojure.core is automatically interned when a new namespace is created?

"It depends." Yes if you use (ns foo) ..., but not apparently if you use (in-ns 'foo) which might be done in certain metaprogramming situations, or during repl experimentation.

 

[Ritchie Cai]

I see. Thanks.