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Difference between binding and binding

What is the difference between Clojure functions binding

and with-bindings

? They seem to do the same thing, but with slightly different syntax.

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3 answers


with bindings is useful when you need to dynamically choose what to bind . here's a fun example where we arbitrarily choose what to bind:

user> (def ^:dynamic a)
#'user/a
user> (def ^:dynamic b)
#'user/b
user> (binding [a 1
                b 2]
        (+ a b))
3
user> (with-bindings (if (rand-nth [true false])
                       {#'a 1
                        #'b (rand-int 10)}
                       {#'a 1
                        #'b 2})
        (+ a b))
3
user> (with-bindings (if (rand-nth [true false])
                       {#'a 1
                        #'b (rand-int 10)}
                       {#'a 1
                        #'b 2})
        (+ a b))
3
user> (with-bindings (if (rand-nth [true false])
                       {#'a 1
                        #'b (rand-int 10)}
                       {#'a 1
                        #'b 2})
        (+ a b))
1


if you try it with with bind

it will get frustrated that it didn't pass a literal vector as an anchor shape.

user> (binding (if (rand-nth [true false])
                 {#'a 1
                  #'b (rand-int 10)}
                 {#'a 1
                  #'b 2})
        (+ a b))
IllegalArgumentException binding requires a vector for its binding in user:138  clojure.core/binding (core.clj:1865)
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It actually does the same thing:



(def ^:dynamic x 1)
;;=> #'user/x

x
;;=> 1

(with-bindings {#'x 2}
   x)
;;=> 2
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You may notice a slight difference in the input parameters: binding

accepts characters, while with-bindings

accepts variables. Also, as mentioned above, since it with-bindings

takes a map, you can compose it dynamically based on your application logic.

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