// Kotlin: Operator Overload (3) // In order to use the range for loops, you would need to implement the rangeTo to return our custom range. That would need to return our custom iterator. We added until method to provide a range also. class Demo(val value: Int) : Comparable { override operator fun compareTo(operand: Demo) = value.compareTo(operand.value) operator fun inc() = Demo(value+1) operator fun rangeTo(that: Demo) = DemoRange(this, that) override fun toString() = "Demo($value)" infix fun until(last: Demo) = DemoRange(this, Demo(last.value-1)) } class DemoIterator(val start: Demo, val endInclusive: Demo) : Iterator { var value = start override fun hasNext() = value <= endInclusive override fun next() = value.also { value++ } } // The override methods are required. hasNext must return false if there is no longer values to retrieve. This stops the iteration. next must return the current value and usually make sure there is another for hasNext. class DemoRange(override val start: Demo, override val endInclusive: Demo) : ClosedRange, Iterable { override fun iterator(): Iterator = DemoIterator(start, endInclusive) override fun toString() = "$start..$endInclusive" } // We override the properties (start and endInclusive) to change their type. We override iterator to return our custom iterator. We override toString so we do not get the default display, but what is normally seen for other ranges. /* Text from the image: Expression Method a > b a.compareTo(b) > 0 a < b a.compareTo(b) < 0 a >= b a.compareTo(b) >= 0 a <= b a.compareTo(b) <= 0 a in b b.contains(a) a !in b !b.contains(a) a-- a.dec() a/b a.div(b) a /= b a.divAssign(b) a == b a?.equals(b) ?: (b === null) a != b !(a?.equals(b) ?: (b === null)) a[i] a.get(i) a[i, j] a.get(i, j) a[i,... j] a.get(i,... j) a++ a.inc() a() a.invoke() a(i) a.invoke(i) a(i, j) a.invoke(i, j) a(i,... j) a.invoke(i,... j) a-b a.minus(b) a -= b a.minusAssign(b) !a a.not() a+b a.plus(b) a += b a.plusAssign(b) a..b a.rangeTo(b) a%b a.rem(b) a %= b a.remAssign(b) a[i] = b a.set(i, b) a[i, j] = b a.set(i, j, b) a[i,... j] = b a.set(i,... j, b) a*b a.times(b) a *= b a.timesAssign(b) -a a.unaryMinus() +a a.unaryPlus() */ fun main(args: Array) { for (element in (Demo(1)..Demo(3)).also { println(it) }) println(element) for (element in (Demo(1) until Demo(4)).also { println(it) }) println(element) }

OperatorOverload(3) kt