anchor.diff:  
     @override
     void insertRenderObjectChild(RenderObject child, IndexedSlot<Element?> slot) {
  -    final ContainerRenderObjectMixin<RenderObject, ContainerParentDataMixin<RenderObject>> renderObject =
  -      this.renderObject as ContainerRenderObjectMixin<RenderObject, ContainerParentDataMixin<RenderObject>>;
  +    final ContainerRenderObjectMixin<RenderObject, ContainerParentDataMixin<RenderObject>> renderObject = this.renderObject;
       assert(renderObject.debugValidateChild(child));
       renderObject.insert(child, after: slot.value?.renderObject);
       assert(renderObject == this.renderObject);
  
positive.code:   @override
    MultiChildRenderObjectWidget get widget => super.widget as MultiChildRenderObjectWidget;
  
    /// The current list of children of this element.
    ///
    /// This list is filtered to hide elements that have been forgotten (using
  
negative.code: 
    @override
    void moveRenderObjectChild(RenderObject child, IndexedSlot<Element?> oldSlot, IndexedSlot<Element?> newSlot) {
      final ContainerRenderObjectMixin<RenderObject, ContainerParentDataMixin<RenderObject>> renderObject = this.renderObject;
      assert(child.parent == renderObject);
      renderObject.move(child, after: newSlot.value?.renderObject);
      assert(renderObject == this.renderObject);
  