Clojure Atoms

Atoms are essential for concurrent programming in Clojure as they provide a way to update values in a thread-safe manner without locking. They are a form of reference type along with refs, vars, and agents. Atoms are designed to hold a single value and provide two main functions: swap! and reset!.

Creating an Atom

An atom can be created using the atom function. Let's create an atom holding the value of 0:

(def my-atom (atom 0))

Modifying an Atom

swap!

The swap! function is used to modify the value of an atom. It takes two arguments: the atom and a function which takes the current value of the atom and returns the updated value.

(swap! my-atom inc)
;; the value of my-atom is now 1

Here, the inc function is used to increment the current value of the atom by 1.

reset!

The reset! function is used to set the value of an atom to a new value.

(reset! my-atom 10)
;; the value of my-atom is now 10

Examples

Let's look at an example where we use an atom to keep track of a counter that is incremented every time a button is pressed.

(def counter (atom 0))

(defn handle-button-click []
  (swap! counter inc))

;; every time the button is clicked, handle-button-click is called
(handle-button-click) ;; the value of counter is now 1
(handle-button-click) ;; the value of counter is now 2

Reading an Atom

The current value of an atom can be obtained using the deref function or the @ reader macro.

(deref my-atom) ;; returns the current value of my-atom
@my-atom ;; equivalent to (deref my-atom)

Conclusion

Atoms are a powerful tool for concurrent programming in Clojure. They provide a way to update values in a thread-safe manner without locking. Atoms are easy to create and use, and they have two main functions: swap! and reset!. When used correctly, atoms can make writing concurrent programs simpler and less error-prone.