[gnome-chess] ChessEngine: make abstract

[Michael Catanzaro <mcatanzaro src gnome org>]

commit 3a1ce12c399f12bf76d11989a7c2ef5db24012c6
Author: Michael Catanzaro <mike catanzaro gmail com>
Date:   Sat May 11 19:35:52 2013 -0500

    ChessEngine: make abstract

 src/chess-engine.vala |   18 +++++-------------
 1 files changed, 5 insertions(+), 13 deletions(-)
---
diff --git a/src/chess-engine.vala b/src/chess-engine.vala
index c1f07a5..c27e203 100644
--- a/src/chess-engine.vala
+++ b/src/chess-engine.vala
@@ -1,4 +1,4 @@
-public class ChessEngine : Object
+public abstract class ChessEngine : Object
 {
     public string binary;
     public string args;
@@ -70,21 +70,13 @@ public class ChessEngine : Object
         stopped ();
     }
 
-    public virtual void start_game ()
-    {
-    }
+    public abstract void start_game ();
 
-    public virtual void request_move ()
-    {
-    }
+    public abstract void request_move ();
 
-    public virtual void report_move (ChessMove move)
-    {
-    }
+    public abstract void report_move (ChessMove move);
 
-    public virtual void undo ()
-    {
-    }
+    public abstract void undo ();
 
     public void stop ()
     {