Element.scala

package test

import collection.mutable.ListBuffer

/**
 * @author Matt Hicks <mhicks@powerscala.org>
 */
trait Element

trait Parentable extends Element {
  type P <: Element
}

trait Childable extends Element {
  type C <: Element
}

trait SingleParent extends Parentable {
  def parent: P
}

trait MultiParent extends Parentable {
  def parents: Seq[P]
}

trait SingleChild extends Childable {
  def child: C
}

trait MultiChild extends Childable {
  def children: Seq[C]
}

trait MutableSingleChild extends SingleChild {
  protected var _child: C = _

  def child = _child

  protected def assignChild(child: C) = synchronized {
    _child = child
  }
}

trait MutableMultiChild extends MultiChild {
  protected val _children = new ListBuffer[C]

  def children: Seq[C] = _children

  protected def addChild(child: C) = synchronized {
    _children += child
  }
}

trait MutableSingleParent extends SingleParent {
  protected var _parent: P = _

  def parent = _parent

  protected def assignParent(parent: P) = _parent = parent
}

trait MutableMultiParent extends MultiParent {
  protected val _parents = new ListBuffer[P]

  def parents: Seq[P] = _parents

  protected def addParent(parent: P) = synchronized {
    _parents += parent
  }
}

class Example(name: String) extends MutableSingleParent with MutableMultiChild {
  override type P = Example
  override type C = Example

  def +=(child: C) = {
    addChild(child)
    child.assignParent(this)
  }

  override def toString = "Example(name = %s, parent = %s)".format(name, parent)
}

object Example {
  def main(args: Array[String]): Unit = {
    val p = new Example("Parent")
    val c1 = new Example("Child1")
    val c2 = new Example("Child2")
    p += c1
    p += c2
    p.children.foreach(println)
  }
}