Composable Builder Pattern using this.type in Scala

composable-builder-with-this-type.scala

trait Buildable[T] {
   def build: T 
}

trait HeadBuilder extends Buildable[String] {
  var eyeColor = "brown"
  var hairColor = "red"
  
  def withEyeColor(color: String): this.type = {
    eyeColor = color
    this
  }
  
  def withHairColor(color: String): this.type = {
    hairColor = color
    this
  }
  
  def build = "eyes: " + eyeColor + ", hair: " + hairColor
}

trait BodyBuilder extends Buildable[String] {
  var limbCount = 4

  def withNumLimbs(count: Int): this.type = {
    limbCount = count
    this
  }  
  
  def build = "limbs: " + limbCount
}

class PersonBuilder extends HeadBuilder with BodyBuilder with Buildable[String] {
  override def build: String = List(super[BodyBuilder].build, super[HeadBuilder].build).mkString(", ")
}

val person = new PersonBuilder().withEyeColor("blue").withNumLimbs(3).build
println(person) // limbs: 3, eyes: blue, hair: red