Destructuring in Clojure - Part 1

Mar 30, 2016 • Yehonathan Sharvit

Introduction

Basically, destructuring allows you to create local bindings in a very succint (and elegant) syntax.

In this article, we will demonstrate the basics of destructuring in clojure, using KLIPSE.

Destructuring a vector

The simplest example is destructuring the first n values of a vector:

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(def point [5 7])

​

(let [[x y] point]

  {:x x

   :y y})

the evaluation will appear here (soon)...

A more advanced example is splitting a vector into a head and a tail:

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(def indexes [1 2 3])

​

(let [[x & more] indexes]

  {:x x :more more})

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the evaluation will appear here (soon)...

It’s also worth noticing that you can bind the entire vector to a local using the :as directive.

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(def indexes [1 2 3])

​

(let [[x & more :as full-list] indexes]

  {:x x :more more :full-list full-list})

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the evaluation will appear here (soon)...

Destructuring a map

Simple destructuring on a map is as easy as choosing a local name and providing the key.

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(def point {:x 5 :y 7})

​

(let [{the-x :x the-y :y} point]

  {:x the-x :y the-y})

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the evaluation will appear here (soon)...

As the example shows, the values of :x and :y are bound to locals with the names the-x and the-y.

Usually, you want to create locals with the same name as the keys of the map.

In this case, the syntax becomes even simpler, using the :keys directive:

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(def point {:x 5 :y 7})

​

(let [{:keys [x y]} point]

  (+ x y))

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the evaluation will appear here (soon)...

As with vectors, you can bind the entire map to a local using the :as directive.

Here is how to combine :keys and :as.

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(def point {:x 5 :y 7})

​

(let [{:keys [x y]} point]

  (+ x y))

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the evaluation will appear here (soon)...

And here is how to combine destructuring of vectors and maps (thank you Paul Salaberria):

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(let [[[one :as vec-one]

       [{:keys [k] :as themap} :as vec-two] :as x]

      [[1] [{:k "val"}]]]

  {:x x

   :one one

   :vec-one vec-one

   :k k

   :themap themap

   :vec-two vec-two})

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the evaluation will appear here (soon)...

In the next article, we will show more advanced usages og destructuring in clojure.

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