I am now using kotlin plugin 0.4.221 while I was using 0.4.214 just yesterday.

In the last couple of weeks I started dabbling in kotlin a bit and wrote a first blogpost about the data class, because the data class was a new concept that I have not yet encountered in one of the many programminglanguages I have used over the years. But that probably means I have just been using the wrong ones all these years. Another new concept for me was the val keyword.

The val keyword tells the compiler that our object is immutable.

To val or not to val

So let’s see what that means.

Let’s make a data class with a val property and a var property.

data class MyClass(var i : Int, val s : String)

And now let’s try and use our class, like this.

java fun main(args : Array<String>) { val c1 = MyClass(1,"t") c1.i = 2 c1.s = "s" } you will get an error on the c1.s = “s” line because s is immutable and has been set in the constructor.

You might have noticed that we instantiated our class with the val keyword as well. this means you can no longer assign another instance to it..

So when I try this.

java c1 = MyClass(1,"s") I will get the same error as before.

So if you want to change an immutable class then you will have to create another instance and start passing that along.

```java data class MyClass(val i : Int, val s : String)

fun main(args : Array<String>) { val c1 = MyClass(1,“t”) println(c1.i) println(c1.s) val c2 = MyClass(c1.i,“s”) println(c2.i) println(c2.s) }```


Immutability is desirable a lot of the time, it protects you from unwanted side effects.

According to wikipedia.

Immutable objects are often useful because they are inherently thread-safe.1 Other benefits are that they are simpler to understand and reason about and offer higher security than mutable objects.