Skip to main content

Simple code: Immutability

Immutability is a special thing that in my mind deserves a short explanation and praise.

If you're familiar with functional programming you surely recognice the concept of immutability because it's a key ingredient of the paradigm. In the world of object oriented programming it's not as used and as easy to use approach but there are ways to incorporate immutability to parts of the code and I strongly suggest you to do so.

Quick intro to immutablity

The basic idea of immutability is unchangeable data. 

Lets take a example.

We have a need to modify a object's property but because the object is immutable we can't just change value but instead we make a copy of the object and while making the copy we provide the new value for the copy. In code it looks something like this.


val pencil = Product(name = "Pencil", category = "Office supply")
val blackMarker = pencil.copy(name = "Black marker")


The same idea can be applied in functions and methods by thinking in terms of not changing the existing data. Functions have a input and a output. To achieve immutability you just have to make sure that what ever is your input it's never changed.

Let's take another example.

We want to increment a integer by one. Traditional mutating version is simply count++. Immutable version is a increment function that takes the current count as a input and as a output it should return the input + 1 without modifying the input object. The immutable function would look something like this.

fun increment(count: Int): Int {
  return count + 1
}


Immutability is such a important concept because when we don't modify the existing data values but instead make copies of the data in new variables we don't introduce state changes within the code and we can always trust that once we have given a value to some object it will always have that same value and nothing else. With these presumptions we can write predictable, testable and readable code.

Next part

In the next part I'll be writing about unit tests.

Comments

Popular posts from this blog

Simple code: Readability

Readability, understandability, two key incredients of great code. Easier said than done, right? What one person finds easy to read and understand another one finds incomprehensible. This is especially true when programmers have different levels of understanding on various subjects e.g. object oriented vs. functional or Node.js vs. Java. Even though there are obvious differences between paradigms and programming ecosystems there are some common conventions and ways to lower the barrier. Different approaches It's natural that in programming things happen sequentally e.g. you can have a list of objects and you need to do various things to the list like filter some values out and count a sum of the remaining objects based on some property. With the given list const stories = [   {name: "authentication", points: 43},   {name: "profile page", points: 11},   {name: "shopping cart", points: 24},   {name: "shopping history", points: 15},   {name: &qu

Simple code: Unit tests

Unit tests are the developers number one safety net. Let that sink in. This is the number one reason for writing unit tests. Unit tests are written by developers for developers to ensure that the code works as expected and handles happy and sad paths correctly. With enough unit test coverage the tests enable a safe environment for refactoring and rewriting code. Unit test scope Unit test should test a single thing, a method or function call and it should test only one use case within. In other words a unit test should test a function with a single input. This is a important guideline to understand. When a unit test tests a function with single input it makes the test isolated, repeatable and predictable. Example of good tests: @Test fun findsAddress() {   val address = findAddress("Stevens street 35", "Southport", "Australia")   assertThat(address).isNotNull() } @Test fun doesNotFindAddress() {   val address = findAddress("Stevens street 697", &q