Scala Design Patterns - Second Edition

Using self types

Self types allow us to easily separate code in our applications, and then require it from other places. Everything gets clearer with an example, so let's have a look at one. Let's assume that we want to be able to persist information into a database:

trait Persister[T] {  def persist(data: T)}

The persist method will do some transformations on the data and then insert it in our database. Of course, our code is well-written, so the database implementations are separated. We have the following for our database:

import scala.collection.mutabletrait Database[T] {  def save(data: T)}trait MemoryDatabase[T] extends Database[T] {  val db: mutable.MutableList[T] = mutable.MutableList.empty    override def save(data: T): Unit = { System.out.println("Saving ...