--- a/truffle/com.oracle.truffle.object/src/com/oracle/truffle/object/LayoutStrategy.java	Wed Oct 07 20:27:40 2015 +0200
+++ b/truffle/com.oracle.truffle.object/src/com/oracle/truffle/object/LayoutStrategy.java	Wed Oct 07 19:15:14 2015 +0200
@@ -29,20 +29,36 @@
 import com.oracle.truffle.api.object.Shape;
 import com.oracle.truffle.object.ShapeImpl.BaseAllocator;
 
-public interface LayoutStrategy {
-    boolean updateShape(DynamicObject object);
+public abstract class LayoutStrategy {
+    public abstract boolean updateShape(DynamicObject object);
+
+    public abstract Shape ensureValid(Shape newShape);
+
+    public abstract Shape ensureSpace(Shape shape, Location location);
 
-    Shape returnCached(Shape newShape);
+    public abstract boolean isAutoExtArray();
+
+    public abstract BaseAllocator createAllocator(Layout shape);
 
-    Shape ensureSpace(Shape shape, Location location);
+    public abstract BaseAllocator createAllocator(Shape shape);
 
-    boolean isAutoExtArray();
+    protected abstract ShapeAndProperty generalizeProperty(Property oldProperty, Object value, Shape currentShape, Shape nextShape);
 
-    Property generalizeProperty(DynamicObject object, Property oldProperty, Object value);
+    public static class ShapeAndProperty {
+        private final Shape shape;
+        private final Property property;
 
-    Property generalizeProperty(DynamicObject object, Property oldProperty, Object value, Shape oldShape, Shape newShape);
+        public ShapeAndProperty(Shape shape, Property property) {
+            this.shape = shape;
+            this.property = property;
+        }
 
-    BaseAllocator createAllocator(Layout shape);
+        public Shape getShape() {
+            return shape;
+        }
 
-    BaseAllocator createAllocator(Shape shape);
+        public Property getProperty() {
+            return property;
+        }
+    }
 }