hi, is there any way to initialize a immutable property in a data class in the constructor? In non-data class I've seen examples for the

lazy

keyword that might can help for me, but I don't know how I could use it in a data class. I want something like in C++ how we define a

const

instance variable in the constructor. Here is an example what I would like to do:

data class MyClass(val property: String) {   # <-- mutable
	init {
		this.property = property.capitalize()
	}
}

instance = MyClass("test")
instance.property # Test
instance.property = "test2" # error, immutable variable

but unfortunately the compiler says

Val cannot be reassigned

when I set

this.property

. Do you know how I could use immutable instance variable here?

Well

val

means immutable, I think you're looking for

var

.

sorry, I made a mistake. immutable.

No you can't initialize a parameter

val

, it is already initalized by the main constructor itself.

unfortunately it raises the following error if I don't use

val

or

var

before the constructor argument:

Data class primary constructor must have only property (val / var) parameters

Ah right that's unfortunate.

@nucc IMO a data class shouldn't have any code in it, I'd go with a top level factory method

why don’t you do the capitalization in a factory method instead?

The problem with that is that the

copy

function leaks the constructor, so I'd be able to do

MyClassFactory("test").copy(property = "test")

to get a "broken" instance.

I need to amend the data and if I put the logic to each class where I want to initialize a

MyClass

object then I need to copy the logic everywhere. Or I should create a factory class, but I don't really want to create a

MyClassFactory

just to do some modification on a string.

I really which there was a

@NoCopy

annotation to avoid stuff like this.

hmm. okay, thanks

what if you add a property to your data class that returns the capitalized string?

yeah, I was thinking on the same.

That works in this case but breaks equality and such when the preprocessing isn't an injective function like

Math.abs

.

yes, it's true, fortunately my transformation is injective.