Use covariant on SpanningWidget

@@ -6,6 +6,7 @@
 - Improve Text rendering
 - Improve Text rendering
 - Add individual cell decoration
 - Add individual cell decoration
 - Improve Bullet Widget
 - Improve Bullet Widget
+- Use covariant on SpanningWidget
 
 
 ## 3.2.0
 ## 3.2.0
 
 

@@ -67,12 +67,10 @@ class _FlexContext extends WidgetContext {
   int lastChild = 0;
   int lastChild = 0;
 
 
   @override
   @override
-  void apply(WidgetContext other) {
-    if (other is _FlexContext) {
+  void apply(_FlexContext other) {
     firstChild = other.firstChild;
     firstChild = other.firstChild;
     lastChild = other.lastChild;
     lastChild = other.lastChild;
   }
   }
-  }
 
 
   @override
   @override
   WidgetContext clone() {
   WidgetContext clone() {
@@ -504,11 +502,9 @@ class Flex extends MultiChildWidget implements SpanningWidget {
   bool get hasMoreWidgets => true;
   bool get hasMoreWidgets => true;
 
 
   @override
   @override
-  void restoreContext(WidgetContext context) {
-    if (context is _FlexContext) {
+  void restoreContext(_FlexContext context) {
     _context.firstChild = context.lastChild;
     _context.firstChild = context.lastChild;
   }
   }
-  }
 
 
   @override
   @override
   WidgetContext saveContext() {
   WidgetContext saveContext() {

@@ -32,14 +32,12 @@ class _GridViewContext extends WidgetContext {
   double? childMainAxis;
   double? childMainAxis;
 
 
   @override
   @override
-  void apply(WidgetContext other) {
-    if (other is _GridViewContext) {
+  void apply(_GridViewContext other) {
     firstChild = other.firstChild;
     firstChild = other.firstChild;
     lastChild = other.lastChild;
     lastChild = other.lastChild;
     childCrossAxis = other.childCrossAxis;
     childCrossAxis = other.childCrossAxis;
     childMainAxis = other.childMainAxis;
     childMainAxis = other.childMainAxis;
   }
   }
-  }
 
 
   @override
   @override
   WidgetContext clone() {
   WidgetContext clone() {
@@ -337,11 +335,9 @@ class GridView extends MultiChildWidget implements SpanningWidget {
   bool get hasMoreWidgets => true;
   bool get hasMoreWidgets => true;
 
 
   @override
   @override
-  void restoreContext(WidgetContext context) {
-    if (context is _GridViewContext) {
+  void restoreContext(_GridViewContext context) {
     _context.firstChild = context.lastChild;
     _context.firstChild = context.lastChild;
   }
   }
-  }
 
 
   @override
   @override
   WidgetContext saveContext() {
   WidgetContext saveContext() {

@@ -34,7 +34,7 @@ import 'widget.dart';
 abstract class WidgetContext {
 abstract class WidgetContext {
   WidgetContext clone();
   WidgetContext clone();
 
 
-  void apply(WidgetContext other);
+  void apply(covariant WidgetContext other);
 }
 }
 
 
 abstract class SpanningWidget extends Widget {
 abstract class SpanningWidget extends Widget {
@@ -48,7 +48,7 @@ abstract class SpanningWidget extends Widget {
 
 
   /// Aplpy the context for next layout
   /// Aplpy the context for next layout
   @protected
   @protected
-  void restoreContext(WidgetContext context);
+  void restoreContext(covariant WidgetContext context);
 }
 }
 
 
 class NewPage extends Widget {
 class NewPage extends Widget {

@@ -141,12 +141,10 @@ class _TableContext extends WidgetContext {
   int lastLine = 0;
   int lastLine = 0;
 
 
   @override
   @override
-  void apply(WidgetContext other) {
-    if (other is _TableContext) {
+  void apply(_TableContext other) {
     firstLine = other.firstLine;
     firstLine = other.firstLine;
     lastLine = other.lastLine;
     lastLine = other.lastLine;
   }
   }
-  }
 
 
   @override
   @override
   WidgetContext clone() {
   WidgetContext clone() {
@@ -425,7 +423,7 @@ class Table extends Widget implements SpanningWidget {
   }
   }
 
 
   @override
   @override
-  void restoreContext(WidgetContext context) {
+  void restoreContext(_TableContext context) {
     _context.apply(context);
     _context.apply(context);
     _context.firstLine = _context.lastLine;
     _context.firstLine = _context.lastLine;
   }
   }

@@ -50,12 +50,10 @@ class _WrapContext extends WidgetContext {
   int lastChild = 0;
   int lastChild = 0;
 
 
   @override
   @override
-  void apply(WidgetContext other) {
-    if (other is _WrapContext) {
+  void apply(_WrapContext other) {
     firstChild = other.firstChild;
     firstChild = other.firstChild;
     lastChild = other.lastChild;
     lastChild = other.lastChild;
   }
   }
-  }
 
 
   @override
   @override
   WidgetContext clone() {
   WidgetContext clone() {
@@ -394,11 +392,9 @@ class Wrap extends MultiChildWidget implements SpanningWidget {
   }
   }
 
 
   @override
   @override
-  void restoreContext(WidgetContext context) {
-    if (context is _WrapContext) {
+  void restoreContext(_WrapContext context) {
     _context.firstChild = context.lastChild;
     _context.firstChild = context.lastChild;
   }
   }
-  }
 
 
   @override
   @override
   WidgetContext saveContext() {
   WidgetContext saveContext() {