domazey/kotlin-bucket

Random stuff in Kotlin language

Kotlin Bucket

Random stuff in Kotlin language

Not null check for multiple arguments.

In this implementation, one can use existing classes Pair and Triple.

fun <A, B> Pair<A?, B?>.takeIfNotNull(): Pair<A, B>? {
  val a = first ?: return null
  val b = second ?: return null
  return Pair(a, b)
}

fun <A, B, C> Triple<A?, B?, C?>.takeIfNotNull(): Triple<A, B, C>? {
  val a = first ?: return null
  val b = second ?: return null
  val c = third ?: return null
  return Triple(a, b, c)
}

fun main() {
  val a: Int? = 32
  val b: Long? = 42
  (a to b).takeIfNotNull()?.let { (a, b) ->
    println("a: $a, b: $b")
  }
}

For shortcut, one could use:

inline fun <A, B, R> Pair<A?, B?>.runIfNotNull(block: (A, B)->R): R? {
  return takeIfNotNull()?.let { (a, b) -> block(a, b) }
}

inline fun <A, B, C, R> Triple<A?, B?, C?>.runIfNotNull(block: (A, B, C)->R): R? {
  return takeIfNotNull()?.let { (a, b, c) -> block(a, b, c) }
}

fun main() {
  val a: Int? = 32
  val b: Long? = 42
  (a to b).runIfNotNull { a, b ->
    println("a: $a, b: $b")
  }
}

Pair, Triple, Quadruple creation

In standard library only Pair has pleasant way of constructing it. Here is what one can do:

Optional: define Quadruple, Quintuple etc...

data class Quadruple<A, B, C, D> (val first: A, val second: B, val third: C, val fourth: D): Serializable {
  override fun toString(): String = "($first, $second, $third, $fourth)"
}

infix fun <A, B> A.nd(second: B): Pair<A, B> = this to second
infix fun <A, B, C> Pair<A, B>.rd(third: C) = Triple(first, second, third)
infix fun <A, B, C, D> Triple<A, B, C>.th(fourth: D) = Quadruple(first, second, third, fourth)

fun main() {
  val pair = 1 nd 2
  val triple = 3 nd 4 rd 5
  val anotherTriple = pair rd 6
  val quadruple = 7 nd 8 rd 9 th 10
}