Comparable selector

selector.kt

import java.util.*
import kotlin.comparisons.compareValuesBy

/**
 * Demonstration of how the compare selectors could be moved to the companion object to prevent object allocations.
 * Else each call to compareTo would create n new objects
 *
 * @author Paul Woitaschek
 */
class Foo(val a: String, val b: Int, val c: Date) : Comparable<Foo> {

  override fun compareTo(other: Foo) = compareValuesBy(this, other, *selectors)

  companion object {
    val selectors: Array<(Foo) -> Comparable<*>?> = arrayOf(Foo::a, Foo::b, Foo::c)
  }
}