How to create a generic function to execute a block of code after checking whether a lateinit proper...

# getting-started

[Waseem]

How to create a generic function to execute a block of code after checking whether a lateinit property is initialized?
Something like

fun KProperty0<*>.doIfInitialized(block: () -> Unit) {
    // todo how to do this????
}

[CLOVIS]

You can't.

The code would be

inline fun <T> KProperty0<T>.ifInitialized(block: (T) -> Unit) {
    if (isInitialized) {
        block(get())
    }
}

but the compiler doesn't allow calling isInitialized on a generic property, because the compiler doesn't allow calling isInitialized on a non-lateinit property:

lateinit var a: String
var b: String = "foo"

println(::a.isInitialized)
println(::b.isInitialized) // compile error: This declaration can only be called on a reference to a lateinit property

Since there is no way to know statically if KProperty0 is a lateinit or not, the compiler cannot allow calling it on a given instance.

[CLOVIS]

If you wanted to propagate the compiler check to the caller, you could in theory write

inline fun <T> @receiver:AccessibleLateinitPropertyLiteral KProperty0<T>.ifInitialized(block: (T) -> Unit) {
    if (isInitialized) {
        block(get())
    }
}

but you can't, because kotlin.internal.AccessibleLateinitPropertyLiteral is not public.

However, the standard library could probably add this function if the maintainer wanted to.

[Ayfri]

You should create an issue with this proposal !

[CLOVIS]

What's the use-case though? It's really not a big improvement...

::a.ifInitialized {
    println(a)
}

if (a::isInitialized) {
    println(a)
}

Not everything needs syntax sugar

[Arun Sudharsan]

We have a lot of lateinit variables in the android view model. We need to destroy them once the scope is over. But since some of them are initialised conditionally, they are blowing up when we try to access the member functions of those lateinit vms. So wanted a clean nice extension function to do this check uniformly. Can you guys propose alternative solutions?

[CLOVIS]

How is the extension function nicer than the if?

[Arun Sudharsan]

variable.ifInitialised { }
looks better to me than if(::variable.isInitialised) {}

[CLOVIS]

It's not going to be variable.ifInitialized , as most it would be ::variable.ifInitialized