foreachSpecialized.kt

package x

fun fn(items: List<String?>) {
    items.foreach(filter.notNull) { value ->
        println("$value")
    }

    items.foreach(map.indexed) { (index,value) ->
        println("$index $value")
    }
}

object map {
    object indexed
}

object filter {
    object notNull
}

inline fun <T> Iterable<T>.foreach(_: map.indexed, body: (Int, T) -> Unit) {
    var index = 0
    for (element in this) {
        body(index++, element)
    }
}

inline fun <T : Any> Iterable<T?>.foreach(_: filter.notNull, body: (T) -> Unit) {
    for (element in this) {
        if (element != null)
            body(element)
    }
}