scala(13)A Tour of Scala: Explicitly Typed Self References

scala(13)A Tour of Scala: Explicitly Typed Self References

Explicitly Typed Self References
…snip…

Subclassing
class Point(xc: Int, yc: Int){
     val x: Int = xc
     val y: Int = yc
     def move(dx: Int, dy: Int): Point =
          new Point(x+dx, y+ dy)
}

class ColorPoint(u: Int, v: Int, c: String) extends Point(u, v) {
     val color: String = c
     def compareWith(pt: ColorPoint) : Boolean =
          (px.x == x) && (pt.y == y) && (pt.color == color)
     override def move(dx: Int, dy: Int) : ColorPoint =
          new ColorPoint(x + dy, y + dy, color)
}

Local Type Inference
Deduce the type from the initialization expression of the variable and return response of the return type.
  def main(args: Array[String]): Unit = {
    valx = 1 + 2 * 3// the type is Int
    def succ(x: Int) :Int = x+ 1// the return type should be :Int and we can ommit it
   

  }

And remember the recursive methods can not deduce the type of return.

Unified Types
All the values are objects in scala.

Variance
package com.sillycat.easyscala.start.tour.tour4

object VariancesTest extends App {
  vars: Stack[Any] = new Stack().push("hello");
  s = s.push(new Object())
  s = s.push(7)
  Console.println(s) //7 java.lang.Object@5b6df84b hello
}

class Stack[+A] {
  def push[B >: A](elem: B): Stack[B] = new Stack[B] {
    overridedef top: B = elem
    overridedef pop: Stack[B] = Stack.this
    overridedef toString() = elem.toString() + " " +
      Stack.this.toString()
  }
  def top: A = sys.error("no element on stack")
  def pop: Stack[A] = sys.error("no element on stack")
  overridedef toString() = ""

}

Views
…snip…

XML Processing
…snip...

References:
http://www.scala-lang.org/node/104
http://www.scala-lang.org/node/124
http://www.scala-lang.org/node/125
http://www.scala-lang.org/node/127
http://www.scala-lang.org/node/128
http://www.scala-lang.org/node/130
http://www.scala-lang.org/node/131

scala(12) http://sillycat.iteye.com/blog/1842158