DiffUtilを使ってRecyclerView.Adapterをいい感じにする ref: http://qiita.com/kubode/items/92c1190a6421ba055cc0

Diff.kt

interface Diffable {
    // otherと同じIDを持つかどうか
    fun isTheSame(other: Diffable): Boolean = equals(other)
    // otherと完全一致するかどうか
    fun isContentsTheSame(other: Diffable): Boolean = equals(other)
}

private class Callback(
        val old: List<Diffable>,
        val new: List<Diffable>
) : DiffUtil.Callback() {

    override fun getOldListSize() = old.size
    override fun getNewListSize() = new.size

    override fun areItemsTheSame(oldItemPosition: Int, newItemPosition: Int): Boolean {
        return old[oldItemPosition].isTheSame(new[newItemPosition])
    }

    override fun areContentsTheSame(oldItemPosition: Int, newItemPosition: Int): Boolean {
        return old[oldItemPosition].isContentsTheSame(new[newItemPosition])
    }
}

fun calculateDiff(
        old: List<Diffable>,
        new: List<Diffable>,
        detectMoves: Boolean = false
): DiffUtil.DiffResult {
    return DiffUtil.calculateDiff(Callback(old, new), detectMoves)
}

file1.txt

class MyAdapter : RecyclerView.Adapter<AbstractViewHolder>() {
    var items: List<Item> by Delegates.observable(emptyList()) { _, old, new ->
        calculateDiff(old, new).dispatchUpdatesTo(this)
    }
}

file3.txt

val adapter = MyAdapter()
recyclerView.adapter = adapter
adapter.items = listOf(Item(0, "Item: 0"))

recyclerView.postDelayed({ adapter.items += Item(1, "Item: 1") }, 1000)

Item.kt

data class Item(val id: Long, val fullName: String) : Diffable {
    override fun isTheSame(other: Diffable) = id == (other as? Item)?.id
}