A builder api for kotlin collections

CollectionUtils.kt

class CollectionBuilder<T, MC: MutableCollection<T>>(private val collection: MC) {
    private var finalized = false

    fun add(element: T)  = collection.add(element)
    fun addAll(elements: Collection<T>) = collection.addAll(elements)

    fun finalize(): Collection<T> {
        if (!finalized) {
            return collection
        } else {
            throw IllegalAccessException("MutableOnlyCollection can only be finalized once")
        }
    }
}

typealias ListBuilder<T> = CollectionBuilder<T, MutableList<T>>
typealias SetBuilder<T> = CollectionBuilder<T, MutableSet<T>>


fun <T> listBuilder(): ListBuilder<T> = CollectionBuilder(mutableListOf())
fun <T> setBuilder(): SetBuilder<T> = CollectionBuilder<T, MutableSet<T>>(mutableSetOf())