More puzzlers

[dkandalov]

FYI I created this repo https://github.com/dkandalov/kotlin-puzzlers which includes some of the puzzlers from this repo and some new puzzlers. In particular these two might be interesting:

• https://github.com/dkandalov/kotlin-puzzlers/blob/master/puzzlers/11-exhaustive-when.kt
  where when needs to be an expression in order to be exhaustive, e.g.:

        fun printClassOf(x: X) = when (x) {
            is X.A -> println("is A")
            is X.B -> println("is B")
        }.exhaustive

        val Unit.exhaustive get() = this

• https://github.com/dkandalov/kotlin-puzzlers/blob/master/puzzlers/13-exhaustive-enum.kts
  where Color.from is extension method on instances of enum, not on the enum class. For this to work enum needs companion object and semicolon:

    enum class Color {
        Red, Green, Blue;
        companion object
    }

    fun Color.Companion.from(s: String) = when (s) {
        "#FF0000" -> Red
        "#00FF00" -> Green
        else -> null
    }

[dkandalov]

Here is one more puzzler from kotlin slack https://github.com/dkandalov/kotlin-puzzlers/blob/master/puzzlers/x-child-apply.kts:

open class Node(val name: String) {
    fun lookup() = "lookup in: $name"
}

class Example : Node("container") {
    fun createChild(name: String): Node? = Node(name)

    val child1 = createChild("child1")?.apply {
        println("child1 ${lookup()}")
    }
    val child2 = createChild("child2").apply {
        println("child2 ${lookup()}")
    }
}

Example()

[Kvest]

fun process(num: Int) = if (num % 2 == 0) {
    print("$num,")
    true
} else {
    false
}

val arr = arrayOf(0, 1, 2, 3, 4, 5)
val result = arr.fold(true) { acc, num ->
    acc && process(num)
}
println(result)

What will be printed?
a) 0,2,4,false
b) 0,2,4,true
c) 0,false
d) 0,1,2,3,4,5,true