// Kotlin: Operator Overload (4) // Progressions require adding the downTo method making a progression and the minus & plus operator to update by step to our class. class Demo(val value: Int) : Comparable { override operator fun compareTo(operand: Demo) = value.compareTo(operand.value) infix fun downTo(last: Demo) = DemoProgression(this, last, Demo(1)) operator fun inc() = Demo(value+1) operator fun minus(that: Demo) = Demo(value-that.value) operator fun plus(that: Demo) = Demo(value+that.value) operator fun rangeTo(that: Demo) = DemoRange(this, that) infix fun until(last: Demo) = DemoRange(this, Demo(last.value-1)) override fun toString() = "Demo($value)" } class DemoIterator(val start: Demo, val endInclusive: Demo) : Iterator { var value = start override fun hasNext() = value <= endInclusive override fun next() = value.also { value++ } } // Create the progression implementing the iterator abstracts and allow adding a step. Note: if you ever wish to reverse the progression, you could add a reversed method. class DemoProgression(val first: Demo, val last: Demo, val step: Demo) : Iterator { var value = first override fun hasNext() = if (first > last) value >= last else value <= last override fun next() = value.also { if (first > last) value -= step else value += step } fun reversed() = DemoProgression(last, first, step) infix fun step(skip: Demo) = DemoProgression(first, last, skip) override fun toString() = if (first <= last) "$first..$last step $step" else "$first downTo $last step $step" } class DemoRange(override val start: Demo, override val endInclusive: Demo) : ClosedRange, Iterable { override fun iterator(): Iterator = DemoIterator(start, endInclusive) // Note: if you ever wish to reverse the range, you could add: fun reversed() = DemoProgression(endInclusive, start, Demo(1)) // Add the step method to make a progression of our range class. infix fun step(skip: Demo) = DemoProgression(start, endInclusive, skip) override fun toString() = "$start..$endInclusive" } fun main(args: Array) { println("Using range...") for (element in (Demo(1)..Demo(3)).also { println(it) }) println(element) for (element in (Demo(1)..Demo(3) step Demo(2)).also { println(it) }) println(element) println("\nUsing downTo...") for (element in (Demo(3) downTo Demo(1)).also { println(it) }) println(element) for (element in (Demo(3) downTo Demo(1) step Demo(2)).also { println(it) }) println(element) println("\nUsing reversed...") for (element in (Demo(1)..Demo(3)).reversed() .also { println(it) }) println(element) for (element in (Demo(3) downTo Demo(1) step Demo(2)).reversed().also { println(it) }) println(element) }

OperatorOverload(4) kt