Iterable, Iterator, operator iterator(), operator hasNext(), operator next()와 for 루프

ForExample.kts

class MyIterable(private val n:Int): Iterable<Int> {
    override fun iterator(): Iterator<Int> = MyIterator(n)
}

class MyIterator(private val max: Int): Iterator<Int> {
    private var n:Int=0
    override fun next():Int = n
    override fun hasNext(): Boolean = n++ < max
}

class IterableLike(private val n:Int) {
    operator fun iterator(): IteratorLike = IteratorLike(n)
}

class IteratorLike(private val max: Int) {
    private var n:Int=0
    operator fun next():Int = n
    operator fun hasNext(): Boolean = n++ < max
}

fun main() {
    val iterable = MyIterable(10)
    val iterator = MyIterator(10)
    val iterableLike = IterableLike(10)
    val iteratorLike = IteratorLike(10)

    var sum = 0
    for(i in iterable) sum += i
    println(sum)

    sum = 0
    for(i in iterator) sum += i
    println(sum)

    sum = 0
    for(i in iterableLike) sum += i
    println(sum)

    sum = 0
    for(i in iteratorLike) sum += i      // For-loop range must have an 'iterator()' method
    println(sum)
}

main()