clojure — correct way to locally override operators such as “+”, “*”, etc

Question

What is the correct way to override a method like \"+\"? Right now I have

(defn- + [x y] (replacement x y))

but this results in warnings on the

Answer 1

Although I don't recommend overriding core functions like +, you could use binding or let for this, it depends on what behavior you want:

(let [+ -] (redu­ce + [1 2 3])) ; -4 
(defn my-pl­us [x] (redu­ce + x))
(let [+ -] (my-p­lus [1 2 3])) ;6
(binding [+ -] (my-p­lus [1 2 3])); -4

Like it has been said in the comments below, binding doesn't work this way anymore since clojure 1.3, since the var should be dynamic and +,-, etc aren't.

For testing purposes/mocking you could however get similar behaviour. In that case look at with-redefs (since clojure 1.3): http://clojuredocs.org/clojure_core/clojure.core/with-redefs

Also see: Let vs. Binding in Clojure