Example of adding optional new behavior to old method without breaking API

Behavior.scala

// say you have a method

def hgetall(key:String,value:String)

// but you want to optionally alter its behaviour, whilst keeping old behaviour as default, hence breaking no existing code

sealed trait Behavior
object Behaviors{
 implicit case object NewB extends Behavior
 implicit case object OldB extends Behavior
}

def hgetall(key:String,value:String)(implicit behave:Behavior=Behaviors.OldB)={
  println(behave) // put your code here
}

hgetall("xxx","yyy")                              //> OldB

import Behaviors.NewB
 
hgetall("xxx","yyy")                              //> NewB