I have subclasses which have `override val`s, which are initialized in the subclass's `init` block. ...

# getting-started

[y]

I have subclasses which have `override val`s, which are initialized in the subclass's init block. I am now getting a warning that such properties must be "initialized, finalized or abstract" and that this behavior is deprecated (soon to be a hard error)
1. is this a new Kotlin change?
2. what is the idiomatic way to solve this, since some of these initialization are a little complex? a dedicated private fun initializer for each initialized value?

[Youssef Shoaib [MOD]]

I think you can place the init block before the `override val`s

[y]

(unless I'm missing something) you can't:

class Bar : Baz() {
    override val foo: Foo // warning: property must be initialized, etc.
    init { 
        foo = something() 
    }
}

however

class Bar : Baz() {
    init { 
        foo = something() // error: variable cannot be initialized before declaration
    }
    override val foo: Foo
}

[y]

sigh. dedicated initializers are making the code quite cumbersome

[Chris Lee]

Is this a new warning for you? Is it from ide or Kotlin compiler?

[y]

from the IDE, and it appears to be a new warning (a coworker does not have it)

[y]

I'm going to guess that this was introduced in Kotlin 1.9.0

[Chris Lee]

Did you recently upgrade to Kotlin 1.9? Intellij 2023.2 was released last week, could that be it?

[y]

yes to both. pretty sure I recently got a popup about said update.

[y]

oh well. not a huge change anyway

[Chris Lee]

If it’s a Kotlin change new to 1.9 it should be in the release notes.

[xoangon]

Both of the snippets that you have above are expected to provide errors. In the first case, you’re trying to reassign a val and in the second, the variable is not yet declared.

For the first case, I think you may have a confusion with the pipeline of a class initialisation in Kotlin. The constructor arguments are those arguments needed to be called to create an instance of the class. The properties outside the constructor and the init block are called afterwards, once you have an instance of the class.

For instance, the following code:

class Bar(val constructorArgument: String) {
    val afterConstructedProperty: String

    init {
        afterConstructedProperty = "stringValue"
    }
}

Has this equivalent code in Java:

[xoangon]

You can see that the constructorArgument is an argument of the Java constructor public Bar(@NotNull String _constructorArgument_), while constructedProperty is declared and assigned after the instance is initialised using the super() call

[y]

I see. but in the first case, why was this previously allowed?

[xoangon]

It feels strange for me, as I understand the execution order as follows:

1. Constructor
2. Block of properties outside the constructor
3. init block
I wonder now if there are cases where this is different. Anyway, it feels confusing to have the initialisation of a constructor argument in the init block of the class

[Chris Lee]

not seeing that (or any) warning for this code (IntelliJ 2023.2, Kotlin 1.9):

public abstract class Baz {
    public abstract val x : Int
}

public class Bar : Baz() {
    override val x: Int

    init {
        x = 5
    }
}

public class Bar1 : Baz() {
    override val x: Int

    init {
        x = something()
    }

    private fun something() : Int = 5
}

[y]

@Chris Lee can you try this?

sealed class Baz {
    abstract val name: String

    class Bar : Baz() {
        override val name
        
        init {
            name = "foobar!"
        }
    }
}

[Chris Lee]

In my setup (IntelliJ 2023.2, Kotlin 1.9) that won’t compile: This property must either have a type annotation, be initialized or be delegated
For similar patterns I tend to only use constructor parameters; in the case where you want to insulate construction from the caller use a companion object:

public sealed class Baz3(public open val name : String) {

    public class Bar3 private constructor(public override val name: String) : Baz3(name) {
        public companion object {
            public fun create(): Bar3 {
                return Bar3("abc")
            }
        }
    }
}

[y]

@Chris Lee thank you! I have changed the Kotlin compiler version (which was, IIRC, 1.8.23) to 1.9 and now it does not compile. (annoyingly I can't change it back)
the pattern with the companion object would also work here, `constructor`s are not very nice with complex initializations, and can't handle fallible initializations

[y]

(well they can if you throw)

[Chris Lee]

good stuff. I rarely use `init`blocks and, when I do, they do very little (a few lines of simple code). Any more complex setup is outside of the class definition, in companion objects or factory classes.

[Klitos Kyriacou]

This compiles ok:

sealed class Baz {
    abstract val name: String

    class Bar : Baz() {
        override val name: String

        init {
            name = "foobar!"
        }
    }
}

[y]

are you on 1.9?

[Klitos Kyriacou]

Yes

[Klitos Kyriacou]

And IJ 2023.2

[Klitos Kyriacou]

Note I've added : String to the override val declaration

[y]

oh yeah. duh.

[y]

are you getting any IDE warnings?

[Klitos Kyriacou]

Just a minor warning that the val declaration and init block can be merged into one statement, but that's to be expected. If the init block were more complicated, the warning would go away.