CODEWITHSUNDEEP
genericskotlin
lotdrops
lotdrops

Reputation: 320

Kotlin: vararg of varargs in constructor

I am trying to implement the Filter class. My first version was the one on this question: Kotlin vararg of A to vararg of B

At that point I had not noticed the recursivity when constructing with a predicate, so I am looking for another way of implementing that.

I've changed it to this class declaration: class Filter<in T>(vararg val predicates: (T) -> Boolean)

I am trying to get this other constructor to work:

constructor(vararg filters: Filter<T>) : this(/* do something */)

I don't know how to map a vararg of filters (which contain a vararg of predicates) into a vararg of predicates that have all the predicates in each filter, especially considering that I cannot invoke any function in the filter class because it has not been initialized at that point.

Also, is there a better way to achieve what I am trying to get (a class that can be created with both an array of predicates or an array of instances of the class itself)?

Upvotes: 1

Views: 3225

Answers (1)

David Soroko
David Soroko

Reputation: 9086

Perhaps something like this:

typealias Predicate<T> = (T) -> Boolean

class Filter<T> {
    private val pred: MutableList<Predicate<T>> = mutableListOf()

    constructor(vararg val predicates: Predicate<T>) {
        predicates.forEach { pred.add(it) }
    }

    constructor(vararg filters: Filter<T>) {
        filters.forEach { pred.addAll(it.pred) }
    }
}

fun main(args: Array<String>) {
    val f1 = Filter<String>({true}, {true})
    val f2 = Filter<String>(f1, f1)
}

Upvotes: 2

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