instantiating a class, there is a field `comment` which I'm initializing by delegation ```sealed cla...

# getting-started

[elect]

instantiating a class, there is a field comment which I'm initializing by delegation

sealed class Type(line: String) {
    val comment by line

However there might be some cases where I need to set it explicitly via constructor.. idiomatic code

sealed class Type(line: String, val comment: String = by line)

what's my best option for this?

[Sam]

I'm guessing you have simplified this code before posting it? It doesn't work in this form because you can't delegate a property to a String. But ignoring that problem, if I've understood what you're trying to do, a good solution might be something like this:

class Type(
    line: String, 
    private val commentProvider: () -> String = { line }
) {
    val comment get() = commentProvider.invoke()
}

[elect]

nice idea, it seems at least the compiler is happy
I'll try it and see where it goes, thanks Sam!

[ephemient]

defining

operator fun <T> (() -> T).getValue(thisRef: Any?, property: KProperty<*>): T = invoke()

enables writing

val comment by commentProvider

but you can't do that in the constructor

[elect]

but nice tip nonetheless, thanks

[ilya.gorbunov]

Why can't you write just
sealed class Type(line: String, val comment: String = line)?

[elect]

because I want it to be assigned via delegation

[elect]

it's an xml