import kotlin.test.*

fun main(args: Array<String>) {
//sampleStart
val collection = listOf(1, 2, 3)
val wrappedCollection = object : AbstractCollection<Any>() {
    override val size: Int = collection.size + 2

    override fun iterator(): Iterator<Any> = iterator {
        yield("first")
        yieldAll(collection)
        yield("last")
    }
}

println(wrappedCollection) // [first, 1, 2, 3, last]
//sampleEnd
}

fun main(args: Array<String>) {
//sampleStart
val iterable = Iterable {
    iterator {
        yield(42)
        yieldAll(1..5 step 2)
    }
}
val result = iterable.mapIndexed { index, value -> "$index: $value" }
println(result) // [0: 42, 1: 1, 2: 3, 3: 5]

// can be iterated many times
repeat(2) {
    val sum = iterable.sum()
    println(sum) // 51
}
//sampleEnd
}