codeUsaShift.kt

fun <I: Item> ItemContainer<I>.codeusaShift(predicate: (I) -> Boolean = Item::isInvalidItem) {
    val tempBank = items
    var id = 0
    tempBank.forEachIndexed { index, item ->
        if (!predicate(item)) {
            items[id] = tempBank[id++]
        }
    }
    for (index in id until items.size) {
        items[index] = InvalidItem
    }
}