Multitype RecyclerView Adapter

Example.kt

recycler_view.withBindings {
            +DateBinding()
            +IncomingMessageBinding()
            +OutgoingMessageBinding()
        }

recycler_view.submitList(listOf<Widget.State>(...))

//**************************************************************//
class DateBinding : ItemBinding<DateWidget.State, DateWidget> {
    override fun onCreateView(context: Context) = DateWidget(context)

    override fun onBindView(view: DateWidget, item: DateWidget.State) {
        view.render(item)
    }
}

class IncomingMessageBinding : ItemBinding<IncomingMessageWidget.State, IncomingMessageWidget> {
    override fun onCreateView(context: Context): IncomingMessageWidget = IncomingMessageWidget(context)

    override fun onBindView(view: IncomingMessageWidget, item: IncomingMessageWidget.State) {
        view.render(item)
    }
}

class OutgoingMessageBinding : ItemBinding<OutgoingMessageWidget.State, OutgoingMessageWidget> {
    override fun onCreateView(context: Context): OutgoingMessageWidget = OutgoingMessageWidget(context)

    override fun onBindView(view: OutgoingMessageWidget, item: OutgoingMessageWidget.State) {
        view.render(item)
    }
}

MultitypeAdapter.kt

import android.content.Context
import android.view.View
import android.view.ViewGroup
import androidx.recyclerview.widget.DiffUtil
import androidx.recyclerview.widget.ListAdapter
import androidx.recyclerview.widget.RecyclerView
import kotlin.reflect.KClass

class MultitypeAdapter : ListAdapter<Any, RecyclerView.ViewHolder>(DiffCallback()) {

    val bindings = mutableMapOf<KClass<*>, ItemBinding<*, *>>()

    inline fun <reified T : Any, reified V : View> register(binding: ItemBinding<T, V>) {
        bindings[T::class] = binding
    }

    inline operator fun <reified T : Any, reified V : View> ItemBinding<T, V>.unaryPlus(){
        register(this)
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder {
        val view = bindings.values.elementAt(viewType).onCreateView(parent.context)
        return ViewHolder(view)
    }

    override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
        val item: Any = getItem(position)
        val viewDelegate = bindings.values.elementAt(holder.itemViewType) as ItemBinding<Any, View>
        viewDelegate.onBindView(holder.itemView, item)
    }

    override fun getItemViewType(position: Int): Int = bindings.keys.indexOf(getItem(position)::class)

    private class ViewHolder(view: View) : RecyclerView.ViewHolder(view)
}

interface ItemBinding<T : Any, V : View> {
    fun onCreateView(context: Context): V
    fun onBindView(view: V, item: T)
}

fun RecyclerView.withBindings(registerTypes: MultitypeAdapter.() -> Unit) {
    adapter = MultitypeAdapter().apply(registerTypes)
}

fun RecyclerView.submitList(list: List<Any>) {
    (adapter as MultitypeAdapter).submitList(list)
}

private class DiffCallback : DiffUtil.ItemCallback<Any>() {
    override fun areItemsTheSame(oldItem: Any, newItem: Any): Boolean = oldItem == newItem

    override fun areContentsTheSame(oldItem: Any, newItem: Any): Boolean = oldItem == newItem
}