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.

Popular posts from this blog

Simple code: Naming things

There are two hard things in programming and naming is one them. If you don't believe me ask Martin Fowler https://www.martinfowler.com/bliki/TwoHardThings.html . In this post I'll be covering some general conventions for naming things to improve readability and understandabilty of the code. There are lots of things that need a name in programming. Starting from higher abstractions to lower we need to name a project, API or library, we probably need to name the source code repository, when we get to the code we need to name our modules or packages, we give names to classes, objects, interfaces and in those we name our functions or methods and within those we name our variables. Overall a lot of things to name. TLDR; Basic rule There's a single basic convention to follow to achiveve better, more descriptive naming of things. Give it a meaningful name i.e. don't use shorthands like gen or single letter variables like a, x, z instead tell what it represents, what it does...

Simple code: Integration tests

Integration test is something that tests a functionality that is dependant on a external system e.g. a database, HTTP API or message queue. Integration vs unit tests The line is thin in my opinion. The integration part can be faked or a embedded services can be used in place of the actual integration point and with these solutions the interaction with the external system is bounded in the test context and the tests can be executed in isolation so they are very much like unit tests. The only difference with this type of integration test and unit test is that the startup time of the embedded or faked system usually takes some seconds and that adds total execution time of the tests. Even though the total test exection time is longer all the tests need to pass and all the cases need to be covered whether there's external systems involved or not so the importance is equal between the test types. This is why I wouldn't separate unit and integration tests from each other within the co...

Simple code: Simplicity

Simplest solutions are usually the best solutions. We as software developers work with hard problems and solve a lot of small problems every day. Solving a hard problem itself is a hard job. Though in my opinion it's not enough to solve a hard problem in any possible way but a hard problem should be solved with a simple solution. When a developer comes up with a simple solution to a hard problem then they can declare the problem solved. First a disclaimer. Coming up with a simple solution to a hard problems is itself a very hard problem and takes a lot of time, effort and practice. I've seen my share of "clever" solutions for hard problems and the problem with those is that usually the solution itself is so hard to understand that depending on the size of the problem it may take a developer from hours to days or even weeks to understand how that "clever" solution works. It's a rare occasion when a developer has come up with a simple solution to a hard pr...