import kotlin.test.*
import kotlin.coroutines.experimental.buildIterator
import kotlin.coroutines.experimental.buildSequence

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> = buildIterator {
        yield("first")
        yieldAll(collection)
        yield("last")
    }
}

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