How to declare generic RecyclerView adapter in Android

Issue #357

generic/Adapter.kt

package com.onmyway133.generic

import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.recyclerview.widget.RecyclerView

abstract class Adapter<T>(var items: ArrayList<T>): RecyclerView.Adapter<RecyclerView.ViewHolder>() {
    abstract fun configure(item: T, holder: ViewHolder)

    fun update(items: ArrayList<T>) {
        this.items = items
        notifyDataSetChanged()
    }

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

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder {
        val view = LayoutInflater
            .from(parent.context)
            .inflate(viewType, parent, false)
        return ViewHolder(view)
    }

    override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
        configure(items[position], holder as ViewHolder)
    }

}

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

hero/HeroAdapter.kt

package com.onmyway133.hero
import kotlinx.android.synthetic.main.hero_item_view.view.*

class Adapter(items: ArrayList<Hero>): com.onmyway133.generic.Adapter<Hero>(items) {
    override fun configure(item: Hero, holder: ViewHolder) {
        holder.itemView.titleLabel.text = item.name
        holder.itemView.descriptionLabel.text = item.description
    }

    override fun getItemViewType(position: Int): Int {
        return R.layout.hero_item_view
    }
}

May run into https://stackoverflow.com/questions/49512629/default-interface-methods-are-only-supported-starting-with-android-n

app/build.gradle

android {
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
}