How can I use Kotlin Function type as a Data type ...

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[Gopal S Akshintala]

How can I use Kotlin Function type as a Data type within Java? For example:
I have a typealias typealias _Validator_<_ValidatableT_, _FailureT_> = _suspend_ (_ValidatableT_) -> _Either_<_FailureT_, Any?>
Within Kotlin, I use it like this as a data type to assign to a lamda val validateParent3X: _Validator_<_Egg_, _ValidationFailure_> = {...}
But I cannot use typealias from Java. What is the idiomatic way to use this Function type as data type on Java?
I see two unknows I have for java interoperability. 1. How can I idimotically refer a Function type 2. Function type being suspend

[Vampire]

This is untested and just out of my head while not being that Kotlin-skilled yet, but I think what you want is kotlin.jvm.functions.Function1<_ValidatableT_, Deferred<_FailureT>_> or something like that.

[araqnid]

typealiases aren’t visible from Java, but you could do it Java style by creating an interface: interface Validator<V, F> { suspend fun validate(input: V): Either<F, Any?> } This won’t address calling a suspend function from Java, though, which is a bigger can of worms.
TBH I’d suggest writing an adapter layer (in Kotlin) that is to be used by Java and exposes simpler interfaces, and adapts a SAM interface where the function returns CompletableFuture<…> or similar