Attempting to remove some of the boilerplate from RecyclerView Adapters. Also off the back of this creating an adapter that accepts a header view similar to iOS tableHeaderView. By using getViewType(position:Int) you can provide different cell types to then create within onCreateItemViewHolder.

HeaderItemAdapter.kt

import android.support.v7.widget.RecyclerView
import android.view.ViewGroup

/**
 * Created by Terence Baker on 08/02/2018.
 */
abstract class HeaderItemAdapter<H : RecyclerView.ViewHolder, I : RecyclerView.ViewHolder, T>(items: Array<T>, itemClickListener: OnRecyclerItemClickListener<T>? = null) : ItemAdapter<I, T>(items, itemClickListener) {

    companion object {

        private const val HEADER = -1
        private const val CELL = 0
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder {

        return when (viewType) {
            HEADER -> onCreateHeaderViewHolder(parent)
            else -> onCreateItemViewHolder(parent, viewType)
        }
    }

    override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {

        if (position == 0) {

            @Suppress("UNCHECKED_CAST")
            (holder as? H)?.let { onBindHeaderViewHolder(it) }
        }
        else {

            super.onBindViewHolder(holder, position - 1)
        }
    }

    override fun getItemViewType(position: Int): Int {

        return when (position) {

            0 -> HEADER
            else -> getViewType(position - 1)
        }
    }

    override fun getItemCount(): Int = items.count() + 1

    abstract fun onCreateHeaderViewHolder(parent: ViewGroup): H
    abstract fun onBindHeaderViewHolder(holder: H)

    internal open fun getViewType(position: Int) = CELL
}

ItemAdapter.kt

import android.support.v7.widget.RecyclerView
import android.view.ViewGroup

/**
 * Created by Terence Baker on 08/02/2018.
 */
abstract class ItemAdapter<I : RecyclerView.ViewHolder, T>(items: Array<T>, private val itemClickListener: OnRecyclerItemClickListener<T>? = null) : RecyclerView.Adapter<RecyclerView.ViewHolder>() {

    open var items: Array<T> = items
        set(value) {
            field = value
            notifyDataSetChanged()
        }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder {

        return onCreateItemViewHolder(parent, viewType)
    }

    override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {

        holder.itemView.setOnClickListener { itemClickListener?.onItemClick(position, items[position]) }

        @Suppress("UNCHECKED_CAST")
        (holder as? I)?.let { onBindItemViewHolder(it, items[position]) }
    }

    abstract fun onCreateItemViewHolder(parent: ViewGroup, viewType: Int): I
    abstract fun onBindItemViewHolder(holder: I, item: T)

    override fun getItemCount(): Int = items.count()
}

OnRecyclerItemClickListener.kt

/**
 * Created by Terence Baker on 08/02/2018.
 */
interface OnRecyclerItemClickListener<in T> {

    fun onItemClick(position: Int, item: T)
}

Sample.kt

class MyAdapter(items: Array<MyObject> = arrayOf(), itemClickListener: OnRecyclerItemClickListener<MyObject> = null) : HeaderItemAdapter<MyHeaderViewHolder, MyViewHolder, MyObject>(items, itemClickListener) {

    override fun onCreateHeaderViewHolder(parent: ViewGroup) = MyHeaderViewHolder(LayoutInflater.from(parent.context).inflate(R.layout.cell_my_header, parent, false))

    override fun onCreateItemViewHolder(parent: ViewGroup, viewType: Int) = MyViewHolder(LayoutInflater.from(parent.context).inflate(R.layout.cell_my, parent, false))

    override fun onBindHeaderViewHolder(holder: MyHeaderViewHolder) {
    
        holder.setup()
    }

    override fun onBindItemViewHolder(holder: MyViewHolder, item: MyObject) {

        holder.setup(item)
    }
}