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Trait

A trait is similar to an abstract class: it can declare several abstract or concrete members and can be extended. It cannot be instantiated. The difference is that a given class can only extend one abstract class, however, it can mixin one to many traits. Also, a trait cannot have constructor arguments.

For instance, we can declare several traits, each declaring different abstract methods, and mixin them all in the Rectangle class:

trait Description {  def description: String}trait Coordinates extends Description {  def x: Int  def y: Int  def description: String =    "Coordinates (" + x + ", " + y + ")"}trait Area {  def area: Double}class Rectangle(val x: Int,                val y: Int,                val width: Int,                val height: Int)  extends Coordinates with Description ...