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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.

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