Use option/some/none for remove disk (#1)

cfurst · Feb 6, 2019 · 47638cf · 47638cf
1 parent f63cb09
commit 47638cf
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Showing 2 changed files with 9 additions and 10 deletions.
diff --git a/src/com/seefurst/towersofhanoi/boardobjects/Board.scala b/src/com/seefurst/towersofhanoi/boardobjects/Board.scala
@@ -25,14 +25,13 @@ class Board(numberOfDisksPerPole: Int) {
    def moveDisk(source: Int, dest: Int) = {
      //System.out.println("calling move disk, beginning pole: " + source + " dest pole: " + dest)
      val sourcePole = poles(source) //index
-     val sourceDisk = sourcePole.removeDisk()
-     //System.out.println("source disk: " + sourceDisk)
-     if (sourceDisk == null ) throw new IllegalStateException;
-
      val destPole = poles(dest) //index
-     destPole.addDisk(sourceDisk)
-
-   }
+     val sourceDiskOption = sourcePole.removeDisk()
+     sourceDiskOption match {
+       case Some(sourceDisk) => destPole.addDisk(sourceDisk)
+       case None => throw new IllegalStateException;
+     }
+  }
 
    def isFinished: Boolean = {
      poles(poles.length - 1).numberOfDisksOnPole == numberOfDisksPerPole

diff --git a/src/com/seefurst/towersofhanoi/boardobjects/Pole.scala b/src/com/seefurst/towersofhanoi/boardobjects/Pole.scala
@@ -29,11 +29,11 @@ class Pole(numberOfDisks: Int) {
     else throw new IllegalArgumentException("disk of size: " + disk.size + " is not allowed on this pole: " + this)
 
   }
-  def removeDisk(): Disk = {
+  def removeDisk(): Option[Disk] = {
     try {
-      disks.pop();
+      Some(disks.pop());
     } catch {
-      case e: EmptyStackException => null // use Option????
+      case e: EmptyStackException => None // use Option????
     }
   }