De-structuring¶

Back in the chapter on reduce, you wrote code to split this series of temperatures:

(def temperatures [[3 9] [2 13] [4 10] [4 9] [4 12] [9 20] [16 21]])

into a vector of minimum and maximum temperatures. Here is my solution:

(defn split-temperatures [result item]
  (let [min-temp (first item)
        max-temp (last item)
        min-vec (first result)
        max-vec (last result)]
    (vector (conj min-vec min-temp) (conj max-vec max-temp))))

As you see, there are a lot of clauses in the let to make the code more readable. You can use de-stucturing to make the code much more compact without losing readability. The idea of de-structuring (I put in the hyphen so you don’t think I am talking about destruction!) is exactly what the name says: you take a structure apart into its components. Instead of the two lines for binding min-temp and max-temp separately, you can de-structure the item vector:

The destructuring, from now on without a hyphen, is here: [min-temp max-temp] item The first element in item is bound to min-temp and the second element in item is bound to max-temp. See if you can modify the preceding code to use destructuring to bind both min-vec and max-vec in one go.

You can also destructure in the parameter list. Here is destructuring in the sum and sum of squares example:

The documentation from clojure.org gives you all the details of destructuring; this page has discussed what they call “sequential destructuring”

The description and examples there are excellent, and I will not attempt to improve on them or even paraphrase them. I recommend that you copy and paste the examples into the following active code area so you can see them in action.