Destructuring in Clojure - Part 2
source link: https://blog.klipse.tech/clojure/2016/03/31/destructuring-part-2.html
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In a precedent post, we have presented the basics of destructuring in Clojure.
Here, we present a trully amazing way of defining default options for a function, leveraging Clojure destructuring.
The need
Let’s say you want to write a function foo that is very cusomizable, something like 27 optional parameters where each parameter has a default value.
How do you write such a function in Clojure?
Think about it for a few minutes before going on…
Think about it for a few more minutes before going on…
The solution
As it often happens, Clojure provides a simple and elegant solution for this complex semantic problem.
There is a cool :or directive available for destructuring.
We will illustrate it with a simple hello-world function that receives two options: language and upper-case?.
The cool thing is that with one line of code, you create local bindings with default values:
{:keys [language upper-case?]
:or {language :en
upper-case? false}
Pay attention to the way the keys are defined inside the :or directive: the keys are defined as symbols, there are no :!
Enough words!
Let’s see it in action, with KLIPSE (feel free to play with the code, inside the article):
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(ns my.args
(:require [clojure.string :as string]))
(defn hello-world [& {:keys [language upper-case?] :or {language :enupper-case? false}}]
(let [greeting (case language
:fr "bonjour monde"
:en "hello world")]
(if upper-case?
(string/upper-case greeting)
greeting)))
(hello-world)
the evaluation will appear here (soon)...
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(hello-world :language :fr)
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the evaluation will appear here (soon)...
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(hello-world :upper-case? true)
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the evaluation will appear here (soon)...
Clojure rocks!
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