Caching results

Memoize.kt

import kotlin.reflect.KProperty
import kotlin.system.measureTimeMillis

class Memoize<T, R>(val fn: (T) -> R) {
    private val cache = mutableMapOf<T, R>()

    operator fun getValue(thisRef: Any?, property: KProperty<*>) =
        { arg: T -> cache.getOrPut(arg) { fn(arg) } }
}

val fib: (Int) -> Long by Memoize { n: Int ->
    when (n) {
        0, 1 -> 1L
        else -> fib(n - 1) + fib(n - 2)
    }
}

fun main() {
    measureTimeMillis { fib(40) }.also(::println)
    measureTimeMillis { fib(45) }.also(::println)
    measureTimeMillis { fib(500) }.also(::println)
}