diff --git a/packages/flutter/lib/src/widgets/actions.dart b/packages/flutter/lib/src/widgets/actions.dart
index 1a83b866c7..6ad3026e56 100644
--- a/packages/flutter/lib/src/widgets/actions.dart
+++ b/packages/flutter/lib/src/widgets/actions.dart
@@ -215,7 +215,7 @@ class Actions extends InheritedWidget {
   // doesn't find one.
   static ActionDispatcher _findDispatcher(Element element) {
     assert(element.widget is Actions);
-    final Actions actions = element.widget;
+    final Actions actions = element.widget as Actions;
     ActionDispatcher dispatcher = actions.dispatcher;
     if (dispatcher == null) {
       bool visitAncestorElement(Element visitedElement) {
@@ -223,7 +223,7 @@ class Actions extends InheritedWidget {
           // Continue visiting.
           return true;
         }
-        final Actions actions = visitedElement.widget;
+        final Actions actions = visitedElement.widget as Actions;
         if (actions.dispatcher == null) {
           // Continue visiting.
           return true;
@@ -250,7 +250,7 @@ class Actions extends InheritedWidget {
   static ActionDispatcher of(BuildContext context, {bool nullOk = false}) {
     assert(context != null);
     final InheritedElement inheritedElement = context.getElementForInheritedWidgetOfExactType<Actions>();
-    final Actions inherited = context.dependOnInheritedElement(inheritedElement);
+    final Actions inherited = context.dependOnInheritedElement(inheritedElement) as Actions;
     assert(() {
       if (nullOk) {
         return true;
@@ -306,7 +306,7 @@ class Actions extends InheritedWidget {
       // Below when we invoke the action, we need to use the dispatcher from the
       // Actions widget where we found the action, in case they need to match.
       actionsElement = element;
-      final Actions actions = element.widget;
+      final Actions actions = element.widget as Actions;
       action = actions.actions[intent.key]?.call();
       // Keep looking if we failed to find and create an action.
       return action == null;
diff --git a/packages/flutter/lib/src/widgets/async.dart b/packages/flutter/lib/src/widgets/async.dart
index ad0898d7bf..b5554ce89f 100644
--- a/packages/flutter/lib/src/widgets/async.dart
+++ b/packages/flutter/lib/src/widgets/async.dart
@@ -268,12 +268,10 @@ class AsyncSnapshot<T> {
   bool operator ==(dynamic other) {
     if (identical(this, other))
       return true;
-    if (other is! AsyncSnapshot<T>)
-      return false;
-    final AsyncSnapshot<T> typedOther = other;
-    return connectionState == typedOther.connectionState
-        && data == typedOther.data
-        && error == typedOther.error;
+    return other is AsyncSnapshot<T>
+        && other.connectionState == connectionState
+        && other.data == data
+        && other.error == error;
   }
 
   @override
diff --git a/packages/flutter/lib/src/widgets/automatic_keep_alive.dart b/packages/flutter/lib/src/widgets/automatic_keep_alive.dart
index ba61134978..aafc4417d0 100644
--- a/packages/flutter/lib/src/widgets/automatic_keep_alive.dart
+++ b/packages/flutter/lib/src/widgets/automatic_keep_alive.dart
@@ -107,7 +107,7 @@ class _AutomaticKeepAliveState extends State<AutomaticKeepAlive> {
   /// the first build of that child has not completed yet.
   ParentDataElement<SliverWithKeepAliveWidget> _getChildElement() {
     assert(mounted);
-    final Element element = context;
+    final Element element = context as Element;
     Element childElement;
     // We use Element.visitChildren rather than context.visitChildElements
     // because we might be called during build, and context.visitChildElements
@@ -132,11 +132,11 @@ class _AutomaticKeepAliveState extends State<AutomaticKeepAlive> {
       childElement = child;
     });
     assert(childElement == null || childElement is ParentDataElement<SliverWithKeepAliveWidget>);
-    return childElement;
+    return childElement as ParentDataElement<SliverWithKeepAliveWidget>;
   }
 
   void _updateParentDataOfChild(ParentDataElement<SliverWithKeepAliveWidget> childElement) {
-    childElement.applyWidgetOutOfTurn(build(context));
+    childElement.applyWidgetOutOfTurn(build(context) as ParentDataWidget<SliverWithKeepAliveWidget>);
   }
 
   VoidCallback _createCallback(Listenable handle) {
diff --git a/packages/flutter/lib/src/widgets/basic.dart b/packages/flutter/lib/src/widgets/basic.dart
index f6cfdf2335..f23b57ea13 100644
--- a/packages/flutter/lib/src/widgets/basic.dart
+++ b/packages/flutter/lib/src/widgets/basic.dart
@@ -1931,7 +1931,7 @@ class LayoutId extends ParentDataWidget<CustomMultiChildLayout> {
   @override
   void applyParentData(RenderObject renderObject) {
     assert(renderObject.parentData is MultiChildLayoutParentData);
-    final MultiChildLayoutParentData parentData = renderObject.parentData;
+    final MultiChildLayoutParentData parentData = renderObject.parentData as MultiChildLayoutParentData;
     if (parentData.id != id) {
       parentData.id = id;
       final AbstractNode targetParent = renderObject.parent;
@@ -2659,7 +2659,7 @@ class _OffstageElement extends SingleChildRenderObjectElement {
   _OffstageElement(Offstage widget) : super(widget);
 
   @override
-  Offstage get widget => super.widget;
+  Offstage get widget => super.widget as Offstage;
 
   @override
   void debugVisitOnstageChildren(ElementVisitor visitor) {
@@ -3528,7 +3528,7 @@ class Positioned extends ParentDataWidget<Stack> {
   @override
   void applyParentData(RenderObject renderObject) {
     assert(renderObject.parentData is StackParentData);
-    final StackParentData parentData = renderObject.parentData;
+    final StackParentData parentData = renderObject.parentData as StackParentData;
     bool needsLayout = false;
 
     if (parentData.left != left) {
@@ -4384,7 +4384,7 @@ class Flexible extends ParentDataWidget<Flex> {
   @override
   void applyParentData(RenderObject renderObject) {
     assert(renderObject.parentData is FlexParentData);
-    final FlexParentData parentData = renderObject.parentData;
+    final FlexParentData parentData = renderObject.parentData as FlexParentData;
     bool needsLayout = false;
 
     if (parentData.flex != flex) {
@@ -5968,13 +5968,13 @@ class _MouseRegionElement extends SingleChildRenderObjectElement {
   @override
   void activate() {
     super.activate();
-    final RenderMouseRegion renderMouseRegion = renderObject;
+    final RenderMouseRegion renderMouseRegion = renderObject as RenderMouseRegion;
     renderMouseRegion.postActivate();
   }
 
   @override
   void deactivate() {
-    final RenderMouseRegion renderMouseRegion = renderObject;
+    final RenderMouseRegion renderMouseRegion = renderObject as RenderMouseRegion;
     renderMouseRegion.preDeactivate();
     super.deactivate();
   }
@@ -6763,7 +6763,7 @@ class KeyedSubtree extends StatelessWidget {
 
   /// Wrap each item in a KeyedSubtree whose key is based on the item's existing key or
   /// the sum of its list index and `baseIndex`.
-  static List<Widget> ensureUniqueKeysForList(Iterable<Widget> items, { int baseIndex = 0 }) {
+  static List<Widget> ensureUniqueKeysForList(List<Widget> items, { int baseIndex = 0 }) {
     if (items == null || items.isEmpty)
       return items;
 
diff --git a/packages/flutter/lib/src/widgets/binding.dart b/packages/flutter/lib/src/widgets/binding.dart
index 80f1b14ed9..15338a3633 100644
--- a/packages/flutter/lib/src/widgets/binding.dart
+++ b/packages/flutter/lib/src/widgets/binding.dart
@@ -535,7 +535,7 @@ mixin WidgetsBinding on BindingBase, ServicesBinding, SchedulerBinding, GestureB
       case 'popRoute':
         return handlePopRoute();
       case 'pushRoute':
-        return handlePushRoute(methodCall.arguments);
+        return handlePushRoute(methodCall.arguments as String);
     }
     return Future<dynamic>.value();
   }
@@ -563,8 +563,8 @@ mixin WidgetsBinding on BindingBase, ServicesBinding, SchedulerBinding, GestureB
   @override
   Future<void> handleSystemMessage(Object systemMessage) async {
     await super.handleSystemMessage(systemMessage);
-    final Map<String, dynamic> message = systemMessage;
-    final String type = message['type'];
+    final Map<String, dynamic> message = systemMessage as Map<String, dynamic>;
+    final String type = message['type'] as String;
     switch (type) {
       case 'memoryPressure':
         handleMemoryPressure();
@@ -821,7 +821,7 @@ mixin WidgetsBinding on BindingBase, ServicesBinding, SchedulerBinding, GestureB
       container: renderView,
       debugShortDescription: '[root]',
       child: rootWidget,
-    ).attachToRenderTree(buildOwner, renderViewElement);
+    ).attachToRenderTree(buildOwner, renderViewElement as RenderObjectToWidgetElement<RenderBox>);
   }
 
   /// Whether the [renderViewElement] has been initialized.
@@ -976,7 +976,7 @@ class RenderObjectToWidgetElement<T extends RenderObject> extends RootRenderObje
   RenderObjectToWidgetElement(RenderObjectToWidgetAdapter<T> widget) : super(widget);
 
   @override
-  RenderObjectToWidgetAdapter<T> get widget => super.widget;
+  RenderObjectToWidgetAdapter<T> get widget => super.widget as RenderObjectToWidgetAdapter<T>;
 
   Element _child;
 
@@ -1019,7 +1019,7 @@ class RenderObjectToWidgetElement<T extends RenderObject> extends RootRenderObje
       // due to a reassemble.
       final Widget newWidget = _newWidget;
       _newWidget = null;
-      update(newWidget);
+      update(newWidget as RenderObjectToWidgetAdapter<T>);
     }
     super.performRebuild();
     assert(_newWidget == null);
@@ -1043,13 +1043,13 @@ class RenderObjectToWidgetElement<T extends RenderObject> extends RootRenderObje
   }
 
   @override
-  RenderObjectWithChildMixin<T> get renderObject => super.renderObject;
+  RenderObjectWithChildMixin<T> get renderObject => super.renderObject as RenderObjectWithChildMixin<T>;
 
   @override
   void insertChildRenderObject(RenderObject child, dynamic slot) {
     assert(slot == _rootChildSlot);
     assert(renderObject.debugValidateChild(child));
-    renderObject.child = child;
+    renderObject.child = child as T;
   }
 
   @override
diff --git a/packages/flutter/lib/src/widgets/color_filter.dart b/packages/flutter/lib/src/widgets/color_filter.dart
index 81d32783f7..5b6ce657ef 100644
--- a/packages/flutter/lib/src/widgets/color_filter.dart
+++ b/packages/flutter/lib/src/widgets/color_filter.dart
@@ -55,6 +55,6 @@ class _ColorFilterRenderObject extends RenderProxyBox {
 
   @override
   void paint(PaintingContext context, Offset offset) {
-    layer = context.pushColorFilter(offset, colorFilter, super.paint, oldLayer: layer);
+    layer = context.pushColorFilter(offset, colorFilter, super.paint, oldLayer: layer as ColorFilterLayer);
   }
 }
diff --git a/packages/flutter/lib/src/widgets/drag_target.dart b/packages/flutter/lib/src/widgets/drag_target.dart
index d568c0f8f5..f504e9b08e 100644
--- a/packages/flutter/lib/src/widgets/drag_target.dart
+++ b/packages/flutter/lib/src/widgets/drag_target.dart
@@ -356,7 +356,7 @@ class _DraggableState<T> extends State<Draggable<T>> {
     _recognizer = null;
   }
 
-  void _routePointer(PointerEvent event) {
+  void _routePointer(PointerDownEvent event) {
     if (widget.maxSimultaneousDrags != null && _activeCount >= widget.maxSimultaneousDrags)
       return;
     _recognizer.addPointer(event);
@@ -368,7 +368,7 @@ class _DraggableState<T> extends State<Draggable<T>> {
     Offset dragStartPoint;
     switch (widget.dragAnchor) {
       case DragAnchor.child:
-        final RenderBox renderObject = context.findRenderObject();
+        final RenderBox renderObject = context.findRenderObject() as RenderBox;
         dragStartPoint = renderObject.globalToLocal(position);
         break;
       case DragAnchor.pointer:
@@ -519,7 +519,8 @@ class _DragTargetState<T> extends State<DragTarget<T>> {
   bool didEnter(_DragAvatar<dynamic> avatar) {
     assert(!_candidateAvatars.contains(avatar));
     assert(!_rejectedAvatars.contains(avatar));
-    if (avatar.data is T && (widget.onWillAccept == null || widget.onWillAccept(avatar.data))) {
+    final dynamic data = avatar.data;
+    if (data is T && (widget.onWillAccept == null || widget.onWillAccept(data))) {
       setState(() {
         _candidateAvatars.add(avatar);
       });
@@ -670,10 +671,11 @@ class _DragAvatar<T> extends Drag {
     // Look for the RenderBoxes that corresponds to the hit target (the hit target
     // widgets build RenderMetaData boxes for us for this purpose).
     for (HitTestEntry entry in path) {
-      if (entry.target is RenderMetaData) {
-        final RenderMetaData renderMetaData = entry.target;
-        if (renderMetaData.metaData is _DragTargetState<T>)
-          yield renderMetaData.metaData;
+      final HitTestTarget target = entry.target;
+      if (target is RenderMetaData) {
+        final dynamic metaData = target.metaData;
+        if (metaData is _DragTargetState<T>)
+          yield metaData;
       }
     }
   }
@@ -701,7 +703,7 @@ class _DragAvatar<T> extends Drag {
   }
 
   Widget _build(BuildContext context) {
-    final RenderBox box = overlayState.context.findRenderObject();
+    final RenderBox box = overlayState.context.findRenderObject() as RenderBox;
     final Offset overlayTopLeft = box.localToGlobal(Offset.zero);
     return Positioned(
       left: _lastOffset.dx - overlayTopLeft.dx,
diff --git a/packages/flutter/lib/src/widgets/draggable_scrollable_sheet.dart b/packages/flutter/lib/src/widgets/draggable_scrollable_sheet.dart
index d236f054c3..73d4222c6a 100644
--- a/packages/flutter/lib/src/widgets/draggable_scrollable_sheet.dart
+++ b/packages/flutter/lib/src/widgets/draggable_scrollable_sheet.dart
@@ -260,7 +260,7 @@ class _DraggableSheetExtent {
 
   set currentExtent(double value) {
     assert(value != null);
-    _currentExtent.value = value.clamp(minExtent, maxExtent);
+    _currentExtent.value = value.clamp(minExtent, maxExtent) as double;
   }
   double get currentExtent => _currentExtent.value;
 
@@ -599,7 +599,7 @@ class _InheritedResetNotifier extends InheritedNotifier<_ResetNotifier> {
       return false;
     }
     assert(widget is _InheritedResetNotifier);
-    final _InheritedResetNotifier inheritedNotifier = widget;
+    final _InheritedResetNotifier inheritedNotifier = widget as _InheritedResetNotifier;
     final bool wasCalled = inheritedNotifier.notifier._wasCalled;
     inheritedNotifier.notifier._wasCalled = false;
     return wasCalled;
diff --git a/packages/flutter/lib/src/widgets/editable_text.dart b/packages/flutter/lib/src/widgets/editable_text.dart
index 4603e0446b..709b89d143 100644
--- a/packages/flutter/lib/src/widgets/editable_text.dart
+++ b/packages/flutter/lib/src/widgets/editable_text.dart
@@ -1375,7 +1375,7 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
       // Clamp the final results to prevent programmatically scrolling to
       // out-of-paragraph-bounds positions when encountering tall fonts/scripts that
       // extend past the ascent.
-      scrollOffset = scrollOffset.clamp(0.0, renderEditable.maxScrollExtent);
+      scrollOffset = scrollOffset.clamp(0.0, renderEditable.maxScrollExtent) as double;
     }
     return scrollOffset;
   }
@@ -1744,7 +1744,7 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
   ///
   /// This property is typically used to notify the renderer of input gestures
   /// when [ignorePointer] is true. See [RenderEditable.ignorePointer].
-  RenderEditable get renderEditable => _editableKey.currentContext.findRenderObject();
+  RenderEditable get renderEditable => _editableKey.currentContext.findRenderObject() as RenderEditable;
 
   @override
   TextEditingValue get textEditingValue => _value;
diff --git a/packages/flutter/lib/src/widgets/fade_in_image.dart b/packages/flutter/lib/src/widgets/fade_in_image.dart
index 132d24723a..810dc0a656 100644
--- a/packages/flutter/lib/src/widgets/fade_in_image.dart
+++ b/packages/flutter/lib/src/widgets/fade_in_image.dart
@@ -428,13 +428,13 @@ class _AnimatedFadeOutFadeInState extends ImplicitlyAnimatedWidgetState<_Animate
     _targetOpacity = visitor(
       _targetOpacity,
       widget.isTargetLoaded ? 1.0 : 0.0,
-      (dynamic value) => Tween<double>(begin: value),
-    );
+      (dynamic value) => Tween<double>(begin: value as double),
+    ) as Tween<double>;
     _placeholderOpacity = visitor(
       _placeholderOpacity,
       widget.isTargetLoaded ? 0.0 : 1.0,
-      (dynamic value) => Tween<double>(begin: value),
-    );
+      (dynamic value) => Tween<double>(begin: value as double),
+    ) as Tween<double>;
   }
 
   @override
diff --git a/packages/flutter/lib/src/widgets/focus_manager.dart b/packages/flutter/lib/src/widgets/focus_manager.dart
index 8a9b85c1a8..d7643bf427 100644
--- a/packages/flutter/lib/src/widgets/focus_manager.dart
+++ b/packages/flutter/lib/src/widgets/focus_manager.dart
@@ -595,7 +595,7 @@ class FocusNode with DiagnosticableTreeMixin, ChangeNotifier {
   ///
   /// Use [nearestScope] to start at this node instead of above it.
   FocusScopeNode get enclosingScope {
-    return ancestors.firstWhere((FocusNode node) => node is FocusScopeNode, orElse: () => null);
+    return ancestors.firstWhere((FocusNode node) => node is FocusScopeNode, orElse: () => null) as FocusScopeNode;
   }
 
   /// Returns the size of the attached widget's [RenderObject], in logical
@@ -1040,7 +1040,7 @@ class FocusScopeNode extends FocusNode {
     // found, a scope doesn't have a focusedChild, or a non-scope is
     // encountered.
     while (primaryFocus is FocusScopeNode && primaryFocus.focusedChild != null) {
-      final FocusScopeNode scope = primaryFocus;
+      final FocusScopeNode scope = primaryFocus as FocusScopeNode;
       primaryFocus = scope.focusedChild;
     }
     if (identical(primaryFocus, this)) {
@@ -1426,7 +1426,7 @@ class FocusManager with DiagnosticableTreeMixin {
     properties.add(FlagProperty('haveScheduledUpdate', value: _haveScheduledUpdate, ifTrue: 'UPDATE SCHEDULED'));
     properties.add(DiagnosticsProperty<FocusNode>('primaryFocus', primaryFocus, defaultValue: null));
     properties.add(DiagnosticsProperty<FocusNode>('nextFocus', _nextFocus, defaultValue: null));
-    final Element element = primaryFocus?.context;
+    final Element element = primaryFocus?.context as Element;
     if (element != null) {
       properties.add(DiagnosticsProperty<String>('primaryFocusCreator', element.debugGetCreatorChain(20)));
     }
diff --git a/packages/flutter/lib/src/widgets/focus_traversal.dart b/packages/flutter/lib/src/widgets/focus_traversal.dart
index 528729d559..364065926b 100644
--- a/packages/flutter/lib/src/widgets/focus_traversal.dart
+++ b/packages/flutter/lib/src/widgets/focus_traversal.dart
@@ -587,7 +587,7 @@ class WidgetOrderFocusTraversalPolicy extends FocusTraversalPolicy with Directio
       }
     }
     while (candidate is FocusScopeNode && candidate.focusedChild != null) {
-      final FocusScopeNode candidateScope = candidate;
+      final FocusScopeNode candidateScope = candidate as FocusScopeNode;
       candidate = candidateScope.focusedChild;
     }
     return candidate;
diff --git a/packages/flutter/lib/src/widgets/framework.dart b/packages/flutter/lib/src/widgets/framework.dart
index 2d22044267..131356da3f 100644
--- a/packages/flutter/lib/src/widgets/framework.dart
+++ b/packages/flutter/lib/src/widgets/framework.dart
@@ -65,8 +65,8 @@ class ObjectKey extends LocalKey {
   bool operator ==(dynamic other) {
     if (other.runtimeType != runtimeType)
       return false;
-    final ObjectKey typedOther = other;
-    return identical(value, typedOther.value);
+    return other is ObjectKey
+        && identical(other.value, value);
   }
 
   @override
@@ -197,7 +197,7 @@ abstract class GlobalKey<T extends State<StatefulWidget>> extends Key {
           assert(element != null);
           assert(element.widget != null);
           assert(element.widget.key != null);
-          final GlobalKey key = element.widget.key;
+          final GlobalKey key = element.widget.key as GlobalKey;
           assert(_registry.containsKey(key));
           duplicates ??= <GlobalKey, Set<Element>>{};
           final Set<Element> elements = duplicates.putIfAbsent(key, () => HashSet<Element>());
@@ -314,8 +314,8 @@ class GlobalObjectKey<T extends State<StatefulWidget>> extends GlobalKey<T> {
   bool operator ==(dynamic other) {
     if (other.runtimeType != runtimeType)
       return false;
-    final GlobalObjectKey<T> typedOther = other;
-    return identical(value, typedOther.value);
+    return other is GlobalObjectKey<T>
+        && identical(other.value, value);
   }
 
   @override
@@ -2957,8 +2957,8 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
   @protected
   Element updateChild(Element child, Widget newWidget, dynamic newSlot) {
     assert(() {
-      if (newWidget != null && newWidget.key is GlobalKey) {
-        final GlobalKey key = newWidget.key;
+      final Key key = newWidget?.key;
+      if (key is GlobalKey) {
         key._debugReserveFor(this);
       }
       return true;
@@ -3015,8 +3015,8 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
     _active = true;
     if (parent != null) // Only assign ownership if the parent is non-null
       _owner = parent.owner;
-    if (widget.key is GlobalKey) {
-      final GlobalKey key = widget.key;
+    final Key key = widget.key;
+    if (key is GlobalKey) {
       key._register(this);
     }
     _updateInheritance();
@@ -3365,8 +3365,8 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
     assert(widget != null);
     assert(depth != null);
     assert(!_active);
-    if (widget.key is GlobalKey) {
-      final GlobalKey key = widget.key;
+    final Key key = widget.key;
+    if (key is GlobalKey) {
       key._unregister(this);
     }
     assert(() {
@@ -3461,7 +3461,7 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
           renderObject.describeForError('The associated render object was'),
         ]);
       }
-      final RenderBox box = renderObject;
+      final RenderBox box = renderObject as RenderBox;
       if (!box.hasSize) {
         throw FlutterError.fromParts(<DiagnosticsNode>[
           ErrorSummary('Cannot get size from a render object that has not been through layout.'),
@@ -3568,7 +3568,7 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
     final InheritedElement ancestor = _inheritedWidgets == null ? null : _inheritedWidgets[T];
     if (ancestor != null) {
       assert(ancestor is InheritedElement);
-      return dependOnInheritedElement(ancestor, aspect: aspect);
+      return dependOnInheritedElement(ancestor, aspect: aspect) as T;
     }
     _hadUnsatisfiedDependencies = true;
     return null;
@@ -3618,7 +3618,7 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
     Element ancestor = _parent;
     while (ancestor != null && ancestor.widget.runtimeType != T)
       ancestor = ancestor._parent;
-    return ancestor?.widget;
+    return ancestor?.widget as T;
   }
 
   // TODO(a14n): Remove this when it goes to stable, https://github.com/flutter/flutter/pull/44189
@@ -3635,7 +3635,7 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
         break;
       ancestor = ancestor._parent;
     }
-    final StatefulElement statefulAncestor = ancestor;
+    final StatefulElement statefulAncestor = ancestor as StatefulElement;
     return statefulAncestor?.state;
   }
 
@@ -3648,8 +3648,8 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
         break;
       ancestor = ancestor._parent;
     }
-    final StatefulElement statefulAncestor = ancestor;
-    return statefulAncestor?.state;
+    final StatefulElement statefulAncestor = ancestor as StatefulElement;
+    return statefulAncestor?.state as T;
   }
 
   // TODO(a14n): Remove this when it goes to stable, https://github.com/flutter/flutter/pull/44189
@@ -3680,7 +3680,7 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
         statefulAncestor = ancestor;
       ancestor = ancestor._parent;
     }
-    return statefulAncestor?.state;
+    return statefulAncestor?.state as T;
   }
 
   // TODO(a14n): Remove this when it goes to stable, https://github.com/flutter/flutter/pull/44189
@@ -3694,11 +3694,10 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
     Element ancestor = _parent;
     while (ancestor != null) {
       if (ancestor is RenderObjectElement && matcher.check(ancestor.renderObject))
-        break;
+        return ancestor.renderObject;
       ancestor = ancestor._parent;
     }
-    final RenderObjectElement renderObjectAncestor = ancestor;
-    return renderObjectAncestor?.renderObject;
+    return null;
   }
 
   @override
@@ -3707,11 +3706,10 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
     Element ancestor = _parent;
     while (ancestor != null) {
       if (ancestor is RenderObjectElement && ancestor.renderObject is T)
-        break;
+        return ancestor.renderObject as T;
       ancestor = ancestor._parent;
     }
-    final RenderObjectElement renderObjectAncestor = ancestor;
-    return renderObjectAncestor?.renderObject;
+    return null;
   }
 
   @override
@@ -3978,7 +3976,7 @@ class _ElementDiagnosticableTreeNode extends DiagnosticableTreeNode {
   @override
   Map<String, Object> toJsonMap(DiagnosticsSerializationDelegate delegate) {
     final Map<String, Object> json = super.toJsonMap(delegate);
-    final Element element = value;
+    final Element element = value as Element;
     json['widgetRuntimeType'] = element.widget?.runtimeType?.toString();
     json['stateful'] = stateful;
     return json;
@@ -4288,7 +4286,7 @@ class StatelessElement extends ComponentElement {
   StatelessElement(StatelessWidget widget) : super(widget);
 
   @override
-  StatelessWidget get widget => super.widget;
+  StatelessWidget get widget => super.widget as StatelessWidget;
 
   @override
   Widget build() => widget.build(this);
@@ -4393,7 +4391,7 @@ class StatefulElement extends ComponentElement {
     // let authors call setState from within didUpdateWidget without triggering
     // asserts.
     _dirty = true;
-    _state._widget = widget;
+    _state._widget = widget as StatefulWidget;
     try {
       _debugSetAllowIgnoredCallsToMarkNeedsBuild(true);
       final dynamic debugCheckForReturnedFuture = _state.didUpdateWidget(oldWidget) as dynamic;
@@ -4511,7 +4509,7 @@ class StatefulElement extends ComponentElement {
       }
       return true;
     }());
-    return super.dependOnInheritedElement(ancestor, aspect: aspect);
+    return super.dependOnInheritedElement(ancestor as InheritedElement, aspect: aspect);
   }
 
   @override
@@ -4543,7 +4541,7 @@ abstract class ProxyElement extends ComponentElement {
   ProxyElement(ProxyWidget widget) : super(widget);
 
   @override
-  ProxyWidget get widget => super.widget;
+  ProxyWidget get widget => super.widget as ProxyWidget;
 
   @override
   Widget build() => widget.child;
@@ -4585,7 +4583,7 @@ class ParentDataElement<T extends RenderObjectWidget> extends ProxyElement {
   ParentDataElement(ParentDataWidget<T> widget) : super(widget);
 
   @override
-  ParentDataWidget<T> get widget => super.widget;
+  ParentDataWidget<T> get widget => super.widget as ParentDataWidget<T>;
 
   @override
   void mount(Element parent, dynamic newSlot) {
@@ -4683,7 +4681,7 @@ class InheritedElement extends ProxyElement {
   InheritedElement(InheritedWidget widget) : super(widget);
 
   @override
-  InheritedWidget get widget => super.widget;
+  InheritedWidget get widget => super.widget as InheritedWidget;
 
   final Map<Element, Object> _dependents = HashMap<Element, Object>();
 
@@ -5023,7 +5021,7 @@ abstract class RenderObjectElement extends Element {
   RenderObjectElement(RenderObjectWidget widget) : super(widget);
 
   @override
-  RenderObjectWidget get widget => super.widget;
+  RenderObjectWidget get widget => super.widget as RenderObjectWidget;
 
   /// The underlying [RenderObject] for this element.
   @override
@@ -5036,7 +5034,7 @@ abstract class RenderObjectElement extends Element {
     Element ancestor = _parent;
     while (ancestor != null && ancestor is! RenderObjectElement)
       ancestor = ancestor._parent;
-    return ancestor;
+    return ancestor as RenderObjectElement;
   }
 
   ParentDataElement<RenderObjectWidget> _findAncestorParentDataElement() {
@@ -5426,7 +5424,7 @@ class SingleChildRenderObjectElement extends RenderObjectElement {
   SingleChildRenderObjectElement(SingleChildRenderObjectWidget widget) : super(widget);
 
   @override
-  SingleChildRenderObjectWidget get widget => super.widget;
+  SingleChildRenderObjectWidget get widget => super.widget as SingleChildRenderObjectWidget;
 
   Element _child;
 
@@ -5457,7 +5455,7 @@ class SingleChildRenderObjectElement extends RenderObjectElement {
 
   @override
   void insertChildRenderObject(RenderObject child, dynamic slot) {
-    final RenderObjectWithChildMixin<RenderObject> renderObject = this.renderObject;
+    final RenderObjectWithChildMixin<RenderObject> renderObject = this.renderObject as RenderObjectWithChildMixin<RenderObject>;
     assert(slot == null);
     assert(renderObject.debugValidateChild(child));
     renderObject.child = child;
@@ -5471,7 +5469,7 @@ class SingleChildRenderObjectElement extends RenderObjectElement {
 
   @override
   void removeChildRenderObject(RenderObject child) {
-    final RenderObjectWithChildMixin<RenderObject> renderObject = this.renderObject;
+    final RenderObjectWithChildMixin<RenderObject> renderObject = this.renderObject as RenderObjectWithChildMixin<RenderObject>;
     assert(renderObject.child == child);
     renderObject.child = null;
     assert(renderObject == this.renderObject);
@@ -5491,7 +5489,7 @@ class MultiChildRenderObjectElement extends RenderObjectElement {
       super(widget);
 
   @override
-  MultiChildRenderObjectWidget get widget => super.widget;
+  MultiChildRenderObjectWidget get widget => super.widget as MultiChildRenderObjectWidget;
 
   /// The current list of children of this element.
   ///
@@ -5508,15 +5506,17 @@ class MultiChildRenderObjectElement extends RenderObjectElement {
 
   @override
   void insertChildRenderObject(RenderObject child, Element slot) {
-    final ContainerRenderObjectMixin<RenderObject, ContainerParentDataMixin<RenderObject>> renderObject = this.renderObject;
+    final ContainerRenderObjectMixin<RenderObject, ContainerParentDataMixin<RenderObject>> renderObject =
+      this.renderObject as ContainerRenderObjectMixin<RenderObject, ContainerParentDataMixin<RenderObject>>;
     assert(renderObject.debugValidateChild(child));
     renderObject.insert(child, after: slot?.renderObject);
     assert(renderObject == this.renderObject);
   }
 
   @override
-  void moveChildRenderObject(RenderObject child, dynamic slot) {
-    final ContainerRenderObjectMixin<RenderObject, ContainerParentDataMixin<RenderObject>> renderObject = this.renderObject;
+  void moveChildRenderObject(RenderObject child, Element slot) {
+    final ContainerRenderObjectMixin<RenderObject, ContainerParentDataMixin<RenderObject>> renderObject =
+      this.renderObject as ContainerRenderObjectMixin<RenderObject, ContainerParentDataMixin<RenderObject>>;
     assert(child.parent == renderObject);
     renderObject.move(child, after: slot?.renderObject);
     assert(renderObject == this.renderObject);
@@ -5524,7 +5524,8 @@ class MultiChildRenderObjectElement extends RenderObjectElement {
 
   @override
   void removeChildRenderObject(RenderObject child) {
-    final ContainerRenderObjectMixin<RenderObject, ContainerParentDataMixin<RenderObject>> renderObject = this.renderObject;
+    final ContainerRenderObjectMixin<RenderObject, ContainerParentDataMixin<RenderObject>> renderObject =
+      this.renderObject as ContainerRenderObjectMixin<RenderObject, ContainerParentDataMixin<RenderObject>>;
     assert(child.parent == renderObject);
     renderObject.remove(child);
     assert(renderObject == this.renderObject);
diff --git a/packages/flutter/lib/src/widgets/gesture_detector.dart b/packages/flutter/lib/src/widgets/gesture_detector.dart
index 938cf17279..c8e04ea1e3 100644
--- a/packages/flutter/lib/src/widgets/gesture_detector.dart
+++ b/packages/flutter/lib/src/widgets/gesture_detector.dart
@@ -954,7 +954,7 @@ class RawGestureDetectorState extends State<RawGestureDetector> {
     }());
     _syncAll(gestures);
     if (!widget.excludeFromSemantics) {
-      final RenderSemanticsGestureHandler semanticsGestureHandler = context.findRenderObject();
+      final RenderSemanticsGestureHandler semanticsGestureHandler = context.findRenderObject() as RenderSemanticsGestureHandler;
       _updateSemanticsForRenderObject(semanticsGestureHandler);
     }
   }
@@ -974,7 +974,7 @@ class RawGestureDetectorState extends State<RawGestureDetector> {
     if (widget.excludeFromSemantics)
       return;
 
-    final RenderSemanticsGestureHandler semanticsGestureHandler = context.findRenderObject();
+    final RenderSemanticsGestureHandler semanticsGestureHandler = context.findRenderObject() as RenderSemanticsGestureHandler;
     assert(() {
       if (semanticsGestureHandler == null) {
         throw FlutterError(
@@ -1135,7 +1135,7 @@ class _DefaultSemanticsGestureDelegate extends SemanticsGestureDelegate {
   }
 
   GestureTapCallback _getTapHandler(Map<Type, GestureRecognizer> recognizers) {
-    final TapGestureRecognizer tap = recognizers[TapGestureRecognizer];
+    final TapGestureRecognizer tap = recognizers[TapGestureRecognizer] as TapGestureRecognizer;
     if (tap == null)
       return null;
     assert(tap is TapGestureRecognizer);
@@ -1152,7 +1152,7 @@ class _DefaultSemanticsGestureDelegate extends SemanticsGestureDelegate {
   }
 
   GestureLongPressCallback _getLongPressHandler(Map<Type, GestureRecognizer> recognizers) {
-    final LongPressGestureRecognizer longPress = recognizers[LongPressGestureRecognizer];
+    final LongPressGestureRecognizer longPress = recognizers[LongPressGestureRecognizer] as LongPressGestureRecognizer;
     if (longPress == null)
       return null;
 
@@ -1170,8 +1170,8 @@ class _DefaultSemanticsGestureDelegate extends SemanticsGestureDelegate {
   }
 
   GestureDragUpdateCallback _getHorizontalDragUpdateHandler(Map<Type, GestureRecognizer> recognizers) {
-    final HorizontalDragGestureRecognizer horizontal = recognizers[HorizontalDragGestureRecognizer];
-    final PanGestureRecognizer pan = recognizers[PanGestureRecognizer];
+    final HorizontalDragGestureRecognizer horizontal = recognizers[HorizontalDragGestureRecognizer] as HorizontalDragGestureRecognizer;
+    final PanGestureRecognizer pan = recognizers[PanGestureRecognizer] as PanGestureRecognizer;
 
     final GestureDragUpdateCallback horizontalHandler = horizontal == null ?
       null :
@@ -1212,8 +1212,8 @@ class _DefaultSemanticsGestureDelegate extends SemanticsGestureDelegate {
   }
 
   GestureDragUpdateCallback _getVerticalDragUpdateHandler(Map<Type, GestureRecognizer> recognizers) {
-    final VerticalDragGestureRecognizer vertical = recognizers[VerticalDragGestureRecognizer];
-    final PanGestureRecognizer pan = recognizers[PanGestureRecognizer];
+    final VerticalDragGestureRecognizer vertical = recognizers[VerticalDragGestureRecognizer] as VerticalDragGestureRecognizer;
+    final PanGestureRecognizer pan = recognizers[PanGestureRecognizer] as PanGestureRecognizer;
 
     final GestureDragUpdateCallback verticalHandler = vertical == null ?
       null :
diff --git a/packages/flutter/lib/src/widgets/heroes.dart b/packages/flutter/lib/src/widgets/heroes.dart
index bd7fe1d493..d3da335551 100644
--- a/packages/flutter/lib/src/widgets/heroes.dart
+++ b/packages/flutter/lib/src/widgets/heroes.dart
@@ -73,7 +73,7 @@ enum HeroFlightDirection {
 // The bounding box for context in ancestorContext coordinate system, or in the global
 // coordinate system when null.
 Rect _boundingBoxFor(BuildContext context, [BuildContext ancestorContext]) {
-  final RenderBox box = context.findRenderObject();
+  final RenderBox box = context.findRenderObject() as RenderBox;
   assert(box != null && box.hasSize);
   return MatrixUtils.transformRect(
       box.getTransformTo(ancestorContext?.findRenderObject()),
@@ -274,8 +274,8 @@ class Hero extends StatefulWidget {
         }
         return true;
       }());
-      final Hero heroWidget = hero.widget;
-      final _HeroState heroState = hero.state;
+      final Hero heroWidget = hero.widget as Hero;
+      final _HeroState heroState = hero.state as _HeroState;
       if (!isUserGestureTransition || heroWidget.transitionOnUserGestures) {
         result[tag] = heroState;
       } else {
@@ -286,10 +286,10 @@ class Hero extends StatefulWidget {
     }
 
     void visitor(Element element) {
-      if (element.widget is Hero) {
-        final StatefulElement hero = element;
-        final Hero heroWidget = element.widget;
-        final Object tag = heroWidget.tag;
+      final Widget widget = element.widget;
+      if (widget is Hero) {
+        final StatefulElement hero = element as StatefulElement;
+        final Object tag = widget.tag;
         assert(tag != null);
         if (Navigator.of(hero) == navigator) {
           inviteHero(hero, tag);
@@ -344,7 +344,7 @@ class _HeroState extends State<Hero> {
   void startFlight({ bool shouldIncludedChildInPlaceholder = false }) {
     _shouldIncludeChild = shouldIncludedChildInPlaceholder;
     assert(mounted);
-    final RenderBox box = context.findRenderObject();
+    final RenderBox box = context.findRenderObject() as RenderBox;
     assert(box != null && box.hasSize);
     setState(() {
       _placeholderSize = box.size;
@@ -489,7 +489,7 @@ class _HeroFlight {
       animation: _proxyAnimation,
       child: shuttle,
       builder: (BuildContext context, Widget child) {
-        final RenderBox toHeroBox = manifest.toHero.context?.findRenderObject();
+        final RenderBox toHeroBox = manifest.toHero.context?.findRenderObject() as RenderBox;
         if (_aborted || toHeroBox == null || !toHeroBox.attached) {
           // The toHero no longer exists or it's no longer the flight's destination.
           // Continue flying while fading out.
@@ -501,7 +501,7 @@ class _HeroFlight {
         } else if (toHeroBox.hasSize) {
           // The toHero has been laid out. If it's no longer where the hero animation is
           // supposed to end up then recreate the heroRect tween.
-          final RenderBox finalRouteBox = manifest.toRoute.subtreeContext?.findRenderObject();
+          final RenderBox finalRouteBox = manifest.toRoute.subtreeContext?.findRenderObject() as RenderBox;
           final Offset toHeroOrigin = toHeroBox.localToGlobal(Offset.zero, ancestor: finalRouteBox);
           if (toHeroOrigin != heroRectTween.end.topLeft) {
             final Rect heroRectEnd = toHeroOrigin & heroRectTween.end.size;
@@ -882,7 +882,7 @@ class HeroController extends NavigatorObserver {
     BuildContext fromHeroContext,
     BuildContext toHeroContext,
   ) {
-    final Hero toHero = toHeroContext.widget;
+    final Hero toHero = toHeroContext.widget as Hero;
     return toHero.child;
   };
 }
diff --git a/packages/flutter/lib/src/widgets/icon_data.dart b/packages/flutter/lib/src/widgets/icon_data.dart
index 8b47d0496a..0321d73fcc 100644
--- a/packages/flutter/lib/src/widgets/icon_data.dart
+++ b/packages/flutter/lib/src/widgets/icon_data.dart
@@ -53,11 +53,11 @@ class IconData {
   bool operator ==(dynamic other) {
     if (runtimeType != other.runtimeType)
       return false;
-    final IconData typedOther = other;
-    return codePoint == typedOther.codePoint
-        && fontFamily == typedOther.fontFamily
-        && fontPackage == typedOther.fontPackage
-        && matchTextDirection == typedOther.matchTextDirection;
+    return other is IconData
+        && other.codePoint == codePoint
+        && other.fontFamily == fontFamily
+        && other.fontPackage == fontPackage
+        && other.matchTextDirection == matchTextDirection;
   }
 
   @override
diff --git a/packages/flutter/lib/src/widgets/icon_theme_data.dart b/packages/flutter/lib/src/widgets/icon_theme_data.dart
index c08a8846b2..2feb8ff274 100644
--- a/packages/flutter/lib/src/widgets/icon_theme_data.dart
+++ b/packages/flutter/lib/src/widgets/icon_theme_data.dart
@@ -81,7 +81,7 @@ class IconThemeData extends Diagnosticable {
   final Color color;
 
   /// An opacity to apply to both explicit and default icon colors.
-  double get opacity => _opacity?.clamp(0.0, 1.0);
+  double get opacity => _opacity?.clamp(0.0, 1.0) as double;
   final double _opacity;
 
   /// The default size for icons.
@@ -103,10 +103,10 @@ class IconThemeData extends Diagnosticable {
   bool operator ==(dynamic other) {
     if (other.runtimeType != runtimeType)
       return false;
-    final IconThemeData typedOther = other;
-    return color == typedOther.color
-        && opacity == typedOther.opacity
-        && size == typedOther.size;
+    return other is IconThemeData
+        && other.color == color
+        && other.opacity == opacity
+        && other.size == size;
   }
 
   @override
diff --git a/packages/flutter/lib/src/widgets/implicit_animations.dart b/packages/flutter/lib/src/widgets/implicit_animations.dart
index 8d21f84ef7..e74eddaa3b 100644
--- a/packages/flutter/lib/src/widgets/implicit_animations.dart
+++ b/packages/flutter/lib/src/widgets/implicit_animations.dart
@@ -740,13 +740,13 @@ class _AnimatedContainerState extends AnimatedWidgetBaseState<AnimatedContainer>
 
   @override
   void forEachTween(TweenVisitor<dynamic> visitor) {
-    _alignment = visitor(_alignment, widget.alignment, (dynamic value) => AlignmentGeometryTween(begin: value));
-    _padding = visitor(_padding, widget.padding, (dynamic value) => EdgeInsetsGeometryTween(begin: value));
-    _decoration = visitor(_decoration, widget.decoration, (dynamic value) => DecorationTween(begin: value));
-    _foregroundDecoration = visitor(_foregroundDecoration, widget.foregroundDecoration, (dynamic value) => DecorationTween(begin: value));
-    _constraints = visitor(_constraints, widget.constraints, (dynamic value) => BoxConstraintsTween(begin: value));
-    _margin = visitor(_margin, widget.margin, (dynamic value) => EdgeInsetsGeometryTween(begin: value));
-    _transform = visitor(_transform, widget.transform, (dynamic value) => Matrix4Tween(begin: value));
+    _alignment = visitor(_alignment, widget.alignment, (dynamic value) => AlignmentGeometryTween(begin: value as AlignmentGeometry)) as AlignmentGeometryTween;
+    _padding = visitor(_padding, widget.padding, (dynamic value) => EdgeInsetsGeometryTween(begin: value as EdgeInsetsGeometry)) as EdgeInsetsGeometryTween;
+    _decoration = visitor(_decoration, widget.decoration, (dynamic value) => DecorationTween(begin: value as Decoration)) as DecorationTween;
+    _foregroundDecoration = visitor(_foregroundDecoration, widget.foregroundDecoration, (dynamic value) => DecorationTween(begin: value as Decoration)) as DecorationTween;
+    _constraints = visitor(_constraints, widget.constraints, (dynamic value) => BoxConstraintsTween(begin: value as BoxConstraints)) as BoxConstraintsTween;
+    _margin = visitor(_margin, widget.margin, (dynamic value) => EdgeInsetsGeometryTween(begin: value as EdgeInsetsGeometry)) as EdgeInsetsGeometryTween;
+    _transform = visitor(_transform, widget.transform, (dynamic value) => Matrix4Tween(begin: value as Matrix4)) as Matrix4Tween;
   }
 
   @override
@@ -829,7 +829,7 @@ class _AnimatedPaddingState extends AnimatedWidgetBaseState<AnimatedPadding> {
 
   @override
   void forEachTween(TweenVisitor<dynamic> visitor) {
-    _padding = visitor(_padding, widget.padding, (dynamic value) => EdgeInsetsGeometryTween(begin: value));
+    _padding = visitor(_padding, widget.padding, (dynamic value) => EdgeInsetsGeometryTween(begin: value as EdgeInsetsGeometry)) as EdgeInsetsGeometryTween;
   }
 
   @override
@@ -923,7 +923,7 @@ class _AnimatedAlignState extends AnimatedWidgetBaseState<AnimatedAlign> {
 
   @override
   void forEachTween(TweenVisitor<dynamic> visitor) {
-    _alignment = visitor(_alignment, widget.alignment, (dynamic value) => AlignmentGeometryTween(begin: value));
+    _alignment = visitor(_alignment, widget.alignment, (dynamic value) => AlignmentGeometryTween(begin: value as AlignmentGeometry)) as AlignmentGeometryTween;
   }
 
   @override
@@ -1069,12 +1069,12 @@ class _AnimatedPositionedState extends AnimatedWidgetBaseState<AnimatedPositione
 
   @override
   void forEachTween(TweenVisitor<dynamic> visitor) {
-    _left = visitor(_left, widget.left, (dynamic value) => Tween<double>(begin: value));
-    _top = visitor(_top, widget.top, (dynamic value) => Tween<double>(begin: value));
-    _right = visitor(_right, widget.right, (dynamic value) => Tween<double>(begin: value));
-    _bottom = visitor(_bottom, widget.bottom, (dynamic value) => Tween<double>(begin: value));
-    _width = visitor(_width, widget.width, (dynamic value) => Tween<double>(begin: value));
-    _height = visitor(_height, widget.height, (dynamic value) => Tween<double>(begin: value));
+    _left = visitor(_left, widget.left, (dynamic value) => Tween<double>(begin: value as double)) as Tween<double>;
+    _top = visitor(_top, widget.top, (dynamic value) => Tween<double>(begin: value as double)) as Tween<double>;
+    _right = visitor(_right, widget.right, (dynamic value) => Tween<double>(begin: value as double)) as Tween<double>;
+    _bottom = visitor(_bottom, widget.bottom, (dynamic value) => Tween<double>(begin: value as double)) as Tween<double>;
+    _width = visitor(_width, widget.width, (dynamic value) => Tween<double>(begin: value as double)) as Tween<double>;
+    _height = visitor(_height, widget.height, (dynamic value) => Tween<double>(begin: value as double)) as Tween<double>;
   }
 
   @override
@@ -1204,12 +1204,12 @@ class _AnimatedPositionedDirectionalState extends AnimatedWidgetBaseState<Animat
 
   @override
   void forEachTween(TweenVisitor<dynamic> visitor) {
-    _start = visitor(_start, widget.start, (dynamic value) => Tween<double>(begin: value));
-    _top = visitor(_top, widget.top, (dynamic value) => Tween<double>(begin: value));
-    _end = visitor(_end, widget.end, (dynamic value) => Tween<double>(begin: value));
-    _bottom = visitor(_bottom, widget.bottom, (dynamic value) => Tween<double>(begin: value));
-    _width = visitor(_width, widget.width, (dynamic value) => Tween<double>(begin: value));
-    _height = visitor(_height, widget.height, (dynamic value) => Tween<double>(begin: value));
+    _start = visitor(_start, widget.start, (dynamic value) => Tween<double>(begin: value as double)) as Tween<double>;
+    _top = visitor(_top, widget.top, (dynamic value) => Tween<double>(begin: value as double)) as Tween<double>;
+    _end = visitor(_end, widget.end, (dynamic value) => Tween<double>(begin: value as double)) as Tween<double>;
+    _bottom = visitor(_bottom, widget.bottom, (dynamic value) => Tween<double>(begin: value as double)) as Tween<double>;
+    _width = visitor(_width, widget.width, (dynamic value) => Tween<double>(begin: value as double)) as Tween<double>;
+    _height = visitor(_height, widget.height, (dynamic value) => Tween<double>(begin: value as double)) as Tween<double>;
   }
 
   @override
@@ -1348,7 +1348,7 @@ class _AnimatedOpacityState extends ImplicitlyAnimatedWidgetState<AnimatedOpacit
 
   @override
   void forEachTween(TweenVisitor<dynamic> visitor) {
-    _opacity = visitor(_opacity, widget.opacity, (dynamic value) => Tween<double>(begin: value));
+    _opacity = visitor(_opacity, widget.opacity, (dynamic value) => Tween<double>(begin: value as double)) as Tween<double>;
   }
 
   @override
@@ -1463,7 +1463,7 @@ class _AnimatedDefaultTextStyleState extends AnimatedWidgetBaseState<AnimatedDef
 
   @override
   void forEachTween(TweenVisitor<dynamic> visitor) {
-    _style = visitor(_style, widget.style, (dynamic value) => TextStyleTween(begin: value));
+    _style = visitor(_style, widget.style, (dynamic value) => TextStyleTween(begin: value as TextStyle)) as TextStyleTween;
   }
 
   @override
@@ -1588,10 +1588,10 @@ class _AnimatedPhysicalModelState extends AnimatedWidgetBaseState<AnimatedPhysic
 
   @override
   void forEachTween(TweenVisitor<dynamic> visitor) {
-    _borderRadius = visitor(_borderRadius, widget.borderRadius, (dynamic value) => BorderRadiusTween(begin: value));
-    _elevation = visitor(_elevation, widget.elevation, (dynamic value) => Tween<double>(begin: value));
-    _color = visitor(_color, widget.color, (dynamic value) => ColorTween(begin: value));
-    _shadowColor = visitor(_shadowColor, widget.shadowColor, (dynamic value) => ColorTween(begin: value));
+    _borderRadius = visitor(_borderRadius, widget.borderRadius, (dynamic value) => BorderRadiusTween(begin: value as BorderRadius)) as BorderRadiusTween;
+    _elevation = visitor(_elevation, widget.elevation, (dynamic value) => Tween<double>(begin: value as double)) as Tween<double>;
+    _color = visitor(_color, widget.color, (dynamic value) => ColorTween(begin: value as Color)) as ColorTween;
+    _shadowColor = visitor(_shadowColor, widget.shadowColor, (dynamic value) => ColorTween(begin: value as Color)) as ColorTween;
   }
 
   @override
diff --git a/packages/flutter/lib/src/widgets/inherited_model.dart b/packages/flutter/lib/src/widgets/inherited_model.dart
index ea1919c8bf..a04b870011 100644
--- a/packages/flutter/lib/src/widgets/inherited_model.dart
+++ b/packages/flutter/lib/src/widgets/inherited_model.dart
@@ -127,7 +127,7 @@ abstract class InheritedModel<T> extends InheritedWidget {
     results.add(model);
 
     assert(model.widget is T);
-    final T modelWidget = model.widget;
+    final T modelWidget = model.widget as T;
     if (modelWidget.isSupportedAspect(aspect))
       return;
 
@@ -171,7 +171,7 @@ abstract class InheritedModel<T> extends InheritedWidget {
 
     final InheritedElement lastModel = models.last;
     for (InheritedElement model in models) {
-      final T value = context.dependOnInheritedElement(model, aspect: aspect);
+      final T value = context.dependOnInheritedElement(model, aspect: aspect) as T;
       if (model == lastModel)
         return value;
     }
@@ -187,11 +187,11 @@ class InheritedModelElement<T> extends InheritedElement {
   InheritedModelElement(InheritedModel<T> widget) : super(widget);
 
   @override
-  InheritedModel<T> get widget => super.widget;
+  InheritedModel<T> get widget => super.widget as InheritedModel<T>;
 
   @override
   void updateDependencies(Element dependent, Object aspect) {
-    final Set<T> dependencies = getDependencies(dependent);
+    final Set<T> dependencies = getDependencies(dependent) as Set<T>;
     if (dependencies != null && dependencies.isEmpty)
       return;
 
@@ -199,13 +199,13 @@ class InheritedModelElement<T> extends InheritedElement {
       setDependencies(dependent, HashSet<T>());
     } else {
       assert(aspect is T);
-      setDependencies(dependent, (dependencies ?? HashSet<T>())..add(aspect));
+      setDependencies(dependent, (dependencies ?? HashSet<T>())..add(aspect as T));
     }
   }
 
   @override
   void notifyDependent(InheritedModel<T> oldWidget, Element dependent) {
-    final Set<T> dependencies = getDependencies(dependent);
+    final Set<T> dependencies = getDependencies(dependent) as Set<T>;
     if (dependencies == null)
       return;
     if (dependencies.isEmpty || widget.updateShouldNotifyDependent(oldWidget, dependencies))
diff --git a/packages/flutter/lib/src/widgets/inherited_notifier.dart b/packages/flutter/lib/src/widgets/inherited_notifier.dart
index dce4e5e839..43d47a32cf 100644
--- a/packages/flutter/lib/src/widgets/inherited_notifier.dart
+++ b/packages/flutter/lib/src/widgets/inherited_notifier.dart
@@ -79,7 +79,7 @@ class _InheritedNotifierElement<T extends Listenable> extends InheritedElement {
   }
 
   @override
-  InheritedNotifier<T> get widget => super.widget;
+  InheritedNotifier<T> get widget => super.widget as InheritedNotifier<T>;
 
   bool _dirty = false;
 
diff --git a/packages/flutter/lib/src/widgets/inherited_theme.dart b/packages/flutter/lib/src/widgets/inherited_theme.dart
index aceeae9bc9..ecae20ab22 100644
--- a/packages/flutter/lib/src/widgets/inherited_theme.dart
+++ b/packages/flutter/lib/src/widgets/inherited_theme.dart
@@ -117,7 +117,7 @@ abstract class InheritedTheme extends InheritedWidget {
     final Set<Type> themeTypes = <Type>{};
     context.visitAncestorElements((Element ancestor) {
       if (ancestor is InheritedElement && ancestor.widget is InheritedTheme) {
-        final InheritedTheme theme = ancestor.widget;
+        final InheritedTheme theme = ancestor.widget as InheritedTheme;
         final Type themeType = theme.runtimeType;
         // Only remember the first theme of any type. This assumes
         // that inherited themes completely shadow ancestors of the
diff --git a/packages/flutter/lib/src/widgets/layout_builder.dart b/packages/flutter/lib/src/widgets/layout_builder.dart
index c479b3bdb5..71382f24d1 100644
--- a/packages/flutter/lib/src/widgets/layout_builder.dart
+++ b/packages/flutter/lib/src/widgets/layout_builder.dart
@@ -43,10 +43,10 @@ class _LayoutBuilderElement<ConstraintType extends Constraints> extends RenderOb
   _LayoutBuilderElement(ConstrainedLayoutBuilder<ConstraintType> widget) : super(widget);
 
   @override
-  ConstrainedLayoutBuilder<ConstraintType> get widget => super.widget;
+  ConstrainedLayoutBuilder<ConstraintType> get widget => super.widget as ConstrainedLayoutBuilder<ConstraintType>;
 
   @override
-  RenderConstrainedLayoutBuilder<ConstraintType, RenderObject> get renderObject => super.renderObject;
+  RenderConstrainedLayoutBuilder<ConstraintType, RenderObject> get renderObject => super.renderObject as RenderConstrainedLayoutBuilder<ConstraintType, RenderObject>;
 
   Element _child;
 
diff --git a/packages/flutter/lib/src/widgets/list_wheel_scroll_view.dart b/packages/flutter/lib/src/widgets/list_wheel_scroll_view.dart
index 7b6cf1380c..96673923f4 100644
--- a/packages/flutter/lib/src/widgets/list_wheel_scroll_view.dart
+++ b/packages/flutter/lib/src/widgets/list_wheel_scroll_view.dart
@@ -245,7 +245,7 @@ class FixedExtentScrollController extends ScrollController {
       'The selectedItem property cannot be read when multiple scroll views are '
       'attached to the same FixedExtentScrollController.',
     );
-    final _FixedExtentScrollPosition position = this.position;
+    final _FixedExtentScrollPosition position = this.position as _FixedExtentScrollPosition;
     return position.itemIndex;
   }
 
@@ -265,7 +265,7 @@ class FixedExtentScrollController extends ScrollController {
     }
 
     await Future.wait<void>(<Future<void>>[
-      for (_FixedExtentScrollPosition position in positions)
+      for (_FixedExtentScrollPosition position in positions.cast<_FixedExtentScrollPosition>())
         position.animateTo(
           itemIndex * position.itemExtent,
           duration: duration,
@@ -279,7 +279,7 @@ class FixedExtentScrollController extends ScrollController {
   /// Jumps the item index position from its current value to the given value,
   /// without animation, and without checking if the new value is in range.
   void jumpToItem(int itemIndex) {
-    for (_FixedExtentScrollPosition position in positions) {
+    for (_FixedExtentScrollPosition position in positions.cast<_FixedExtentScrollPosition>()) {
       position.jumpTo(itemIndex * position.itemExtent);
     }
   }
@@ -386,7 +386,7 @@ class _FixedExtentScrollPosition extends ScrollPositionWithSingleContext impleme
        );
 
   static double _getItemExtentFromScrollContext(ScrollContext context) {
-    final _FixedExtentScrollableState scrollable = context;
+    final _FixedExtentScrollableState scrollable = context as _FixedExtentScrollableState;
     return scrollable.itemExtent;
   }
 
@@ -451,7 +451,7 @@ class _FixedExtentScrollable extends Scrollable {
 class _FixedExtentScrollableState extends ScrollableState {
   double get itemExtent {
     // Downcast because only _FixedExtentScrollable can make _FixedExtentScrollableState.
-    final _FixedExtentScrollable actualWidget = widget;
+    final _FixedExtentScrollable actualWidget = widget as _FixedExtentScrollable;
     return actualWidget.itemExtent;
   }
 }
@@ -483,7 +483,7 @@ class FixedExtentScrollPhysics extends ScrollPhysics {
       'the FixedExtentScrollController'
     );
 
-    final _FixedExtentScrollPosition metrics = position;
+    final _FixedExtentScrollPosition metrics = position as _FixedExtentScrollPosition;
 
     // Scenario 1:
     // If we're out of range and not headed back in range, defer to the parent
@@ -711,7 +711,7 @@ class _ListWheelScrollViewState extends State<ListWheelScrollView> {
     super.initState();
     scrollController = widget.controller ?? FixedExtentScrollController();
     if (widget.controller is FixedExtentScrollController) {
-      final FixedExtentScrollController controller = widget.controller;
+      final FixedExtentScrollController controller = widget.controller as FixedExtentScrollController;
       _lastReportedItemIndex = controller.initialItem;
     }
   }
@@ -736,7 +736,7 @@ class _ListWheelScrollViewState extends State<ListWheelScrollView> {
             && widget.onSelectedItemChanged != null
             && notification is ScrollUpdateNotification
             && notification.metrics is FixedExtentMetrics) {
-          final FixedExtentMetrics metrics = notification.metrics;
+          final FixedExtentMetrics metrics = notification.metrics as FixedExtentMetrics;
           final int currentItemIndex = metrics.itemIndex;
           if (currentItemIndex != _lastReportedItemIndex) {
             _lastReportedItemIndex = currentItemIndex;
@@ -776,10 +776,10 @@ class ListWheelElement extends RenderObjectElement implements ListWheelChildMana
   ListWheelElement(ListWheelViewport widget) : super(widget);
 
   @override
-  ListWheelViewport get widget => super.widget;
+  ListWheelViewport get widget => super.widget as ListWheelViewport;
 
   @override
-  RenderListWheelViewport get renderObject => super.renderObject;
+  RenderListWheelViewport get renderObject => super.renderObject as RenderListWheelViewport;
 
   // We inflate widgets at two different times:
   //  1. When we ourselves are told to rebuild (see performRebuild).
@@ -870,11 +870,11 @@ class ListWheelElement extends RenderObjectElement implements ListWheelChildMana
 
   @override
   Element updateChild(Element child, Widget newWidget, dynamic newSlot) {
-    final ListWheelParentData oldParentData = child?.renderObject?.parentData;
+    final ListWheelParentData oldParentData = child?.renderObject?.parentData as ListWheelParentData;
     final Element newChild = super.updateChild(child, newWidget, newSlot);
-    final ListWheelParentData newParentData = newChild?.renderObject?.parentData;
+    final ListWheelParentData newParentData = newChild?.renderObject?.parentData as ListWheelParentData;
     if (newParentData != null) {
-      newParentData.index = newSlot;
+      newParentData.index = newSlot as int;
       if (oldParentData != null)
         newParentData.offset = oldParentData.offset;
     }
@@ -886,7 +886,7 @@ class ListWheelElement extends RenderObjectElement implements ListWheelChildMana
   void insertChildRenderObject(RenderObject child, int slot) {
     final RenderListWheelViewport renderObject = this.renderObject;
     assert(renderObject.debugValidateChild(child));
-    renderObject.insert(child, after: _childElements[slot - 1]?.renderObject);
+    renderObject.insert(child as RenderBox, after: _childElements[slot - 1]?.renderObject as RenderBox);
     assert(renderObject == this.renderObject);
   }
 
@@ -901,7 +901,7 @@ class ListWheelElement extends RenderObjectElement implements ListWheelChildMana
   @override
   void removeChildRenderObject(RenderObject child) {
     assert(child.parent == renderObject);
-    renderObject.remove(child);
+    renderObject.remove(child as RenderBox);
   }
 
   @override
@@ -1018,7 +1018,7 @@ class ListWheelViewport extends RenderObjectWidget {
 
   @override
   RenderListWheelViewport createRenderObject(BuildContext context) {
-    final ListWheelElement childManager = context;
+    final ListWheelElement childManager = context as ListWheelElement;
     return RenderListWheelViewport(
       childManager: childManager,
       offset: offset,
diff --git a/packages/flutter/lib/src/widgets/localizations.dart b/packages/flutter/lib/src/widgets/localizations.dart
index 2161222dbe..5ae0b6e7eb 100644
--- a/packages/flutter/lib/src/widgets/localizations.dart
+++ b/packages/flutter/lib/src/widgets/localizations.dart
@@ -535,12 +535,12 @@ class _LocalizationsState extends State<Localizations> {
 
   T resourcesFor<T>(Type type) {
     assert(type != null);
-    final T resources = _typeToResources[type];
+    final T resources = _typeToResources[type] as T;
     return resources;
   }
 
   TextDirection get _textDirection {
-    final WidgetsLocalizations resources = _typeToResources[WidgetsLocalizations];
+    final WidgetsLocalizations resources = _typeToResources[WidgetsLocalizations] as WidgetsLocalizations;
     assert(resources != null);
     return resources.textDirection;
   }
diff --git a/packages/flutter/lib/src/widgets/media_query.dart b/packages/flutter/lib/src/widgets/media_query.dart
index ad4371641e..39230555d9 100644
--- a/packages/flutter/lib/src/widgets/media_query.dart
+++ b/packages/flutter/lib/src/widgets/media_query.dart
@@ -535,21 +535,21 @@ class MediaQueryData {
   bool operator ==(Object other) {
     if (other.runtimeType != runtimeType)
       return false;
-    final MediaQueryData typedOther = other;
-    return typedOther.size == size
-        && typedOther.devicePixelRatio == devicePixelRatio
-        && typedOther.textScaleFactor == textScaleFactor
-        && typedOther.platformBrightness == platformBrightness
-        && typedOther.padding == padding
-        && typedOther.viewPadding == viewPadding
-        && typedOther.viewInsets == viewInsets
-        && typedOther.physicalDepth == physicalDepth
-        && typedOther.alwaysUse24HourFormat == alwaysUse24HourFormat
-        && typedOther.highContrast == highContrast
-        && typedOther.disableAnimations == disableAnimations
-        && typedOther.invertColors == invertColors
-        && typedOther.accessibleNavigation == accessibleNavigation
-        && typedOther.boldText == boldText;
+    return other is MediaQueryData
+        && other.size == size
+        && other.devicePixelRatio == devicePixelRatio
+        && other.textScaleFactor == textScaleFactor
+        && other.platformBrightness == platformBrightness
+        && other.padding == padding
+        && other.viewPadding == viewPadding
+        && other.viewInsets == viewInsets
+        && other.physicalDepth == physicalDepth
+        && other.alwaysUse24HourFormat == alwaysUse24HourFormat
+        && other.highContrast == highContrast
+        && other.disableAnimations == disableAnimations
+        && other.invertColors == invertColors
+        && other.accessibleNavigation == accessibleNavigation
+        && other.boldText == boldText;
   }
 
   @override
diff --git a/packages/flutter/lib/src/widgets/modal_barrier.dart b/packages/flutter/lib/src/widgets/modal_barrier.dart
index 5f64a5b77a..1a1ea57b8f 100644
--- a/packages/flutter/lib/src/widgets/modal_barrier.dart
+++ b/packages/flutter/lib/src/widgets/modal_barrier.dart
@@ -152,7 +152,7 @@ class AnimatedModalBarrier extends AnimatedWidget {
   ///
   ///  * [ModalRoute.barrierColor], which controls this property for the
   ///    [AnimatedModalBarrier] built by [ModalRoute] pages.
-  Animation<Color> get color => listenable;
+  Animation<Color> get color => listenable as Animation<Color>;
 
   /// Whether touching the barrier will pop the current route off the [Navigator].
   ///
diff --git a/packages/flutter/lib/src/widgets/navigator.dart b/packages/flutter/lib/src/widgets/navigator.dart
index 0831bfda1b..344249fec6 100644
--- a/packages/flutter/lib/src/widgets/navigator.dart
+++ b/packages/flutter/lib/src/widgets/navigator.dart
@@ -1626,7 +1626,7 @@ class NavigatorState extends State<Navigator> with TickerProviderStateMixin {
       isInitialRoute: _history.isEmpty,
       arguments: arguments,
     );
-    Route<T> route = widget.onGenerateRoute(settings);
+    Route<T> route = widget.onGenerateRoute(settings) as Route<T>;
     if (route == null && !allowNull) {
       assert(() {
         if (widget.onUnknownRoute == null) {
@@ -1641,7 +1641,7 @@ class NavigatorState extends State<Navigator> with TickerProviderStateMixin {
         }
         return true;
       }());
-      route = widget.onUnknownRoute(settings);
+      route = widget.onUnknownRoute(settings) as Route<T>;
       assert(() {
         if (route == null) {
           throw FlutterError.fromParts(<DiagnosticsNode>[
@@ -2073,7 +2073,7 @@ class NavigatorState extends State<Navigator> with TickerProviderStateMixin {
   ///    to define the route's `willPop` method.
   @optionalTypeArgs
   Future<bool> maybePop<T extends Object>([ T result ]) async {
-    final Route<T> route = _history.last;
+    final Route<T> route = _history.last as Route<T>;
     assert(route._navigator == this);
     final RoutePopDisposition disposition = await route.willPop();
     if (disposition != RoutePopDisposition.bubble && mounted) {
diff --git a/packages/flutter/lib/src/widgets/nested_scroll_view.dart b/packages/flutter/lib/src/widgets/nested_scroll_view.dart
index b53a02774e..213f85c6d6 100644
--- a/packages/flutter/lib/src/widgets/nested_scroll_view.dart
+++ b/packages/flutter/lib/src/widgets/nested_scroll_view.dart
@@ -610,7 +610,7 @@ class _NestedScrollCoordinator implements ScrollActivityDelegate, ScrollHoldCont
   ScrollActivity createInnerBallisticScrollActivity(_NestedScrollPosition position, double velocity) {
     return position.createBallisticScrollActivity(
       position.physics.createBallisticSimulation(
-        velocity == 0 ? position : _getMetrics(position, velocity),
+        velocity == 0 ? position as ScrollMetrics : _getMetrics(position, velocity),
         velocity,
       ),
       mode: _NestedBallisticScrollActivityMode.inner,
@@ -621,7 +621,7 @@ class _NestedScrollCoordinator implements ScrollActivityDelegate, ScrollHoldCont
     assert(innerPosition != null);
     double pixels, minRange, maxRange, correctionOffset, extra;
     if (innerPosition.pixels == innerPosition.minScrollExtent) {
-      pixels = _outerPosition.pixels.clamp(_outerPosition.minScrollExtent, _outerPosition.maxScrollExtent); // TODO(ianh): gracefully handle out-of-range outer positions
+      pixels = _outerPosition.pixels.clamp(_outerPosition.minScrollExtent, _outerPosition.maxScrollExtent) as double; // TODO(ianh): gracefully handle out-of-range outer positions
       minRange = _outerPosition.minScrollExtent;
       maxRange = _outerPosition.maxScrollExtent;
       assert(minRange <= maxRange);
@@ -687,7 +687,7 @@ class _NestedScrollCoordinator implements ScrollActivityDelegate, ScrollHoldCont
 
   double unnestOffset(double value, _NestedScrollPosition source) {
     if (source == _outerPosition)
-      return value.clamp(_outerPosition.minScrollExtent, _outerPosition.maxScrollExtent);
+      return value.clamp(_outerPosition.minScrollExtent, _outerPosition.maxScrollExtent) as double;
     if (value < source.minScrollExtent)
       return value - source.minScrollExtent + _outerPosition.minScrollExtent;
     return value - source.minScrollExtent + _outerPosition.maxScrollExtent;
@@ -695,7 +695,7 @@ class _NestedScrollCoordinator implements ScrollActivityDelegate, ScrollHoldCont
 
   double nestOffset(double value, _NestedScrollPosition target) {
     if (target == _outerPosition)
-      return value.clamp(_outerPosition.minScrollExtent, _outerPosition.maxScrollExtent);
+      return value.clamp(_outerPosition.minScrollExtent, _outerPosition.maxScrollExtent) as double;
     if (value < _outerPosition.minScrollExtent)
       return value - _outerPosition.minScrollExtent + target.minScrollExtent;
     if (value > _outerPosition.maxScrollExtent)
@@ -987,7 +987,7 @@ class _NestedScrollPosition extends ScrollPosition implements ScrollActivityDele
     // The logic for max is equivalent but on the other side.
     final double max = delta > 0.0 ? double.infinity : math.max(maxScrollExtent, pixels);
     final double oldPixels = pixels;
-    final double newPixels = (pixels - delta).clamp(min, max);
+    final double newPixels = (pixels - delta).clamp(min, max) as double;
     final double clampedDelta = newPixels - pixels;
     if (clampedDelta == 0.0)
       return delta;
@@ -1152,7 +1152,7 @@ class _NestedInnerBallisticScrollActivity extends BallisticScrollActivity {
   final _NestedScrollCoordinator coordinator;
 
   @override
-  _NestedScrollPosition get delegate => super.delegate;
+  _NestedScrollPosition get delegate => super.delegate as _NestedScrollPosition;
 
   @override
   void resetActivity() {
@@ -1185,7 +1185,7 @@ class _NestedOuterBallisticScrollActivity extends BallisticScrollActivity {
   final _NestedScrollMetrics metrics;
 
   @override
-  _NestedScrollPosition get delegate => super.delegate;
+  _NestedScrollPosition get delegate => super.delegate as _NestedScrollPosition;
 
   @override
   void resetActivity() {
@@ -1215,7 +1215,7 @@ class _NestedOuterBallisticScrollActivity extends BallisticScrollActivity {
         done = true;
       }
     } else {
-      value = value.clamp(metrics.minRange, metrics.maxRange);
+      value = value.clamp(metrics.minRange, metrics.maxRange) as double;
       done = true;
     }
     final bool result = super.applyMoveTo(value + metrics.correctionOffset);
diff --git a/packages/flutter/lib/src/widgets/overlay.dart b/packages/flutter/lib/src/widgets/overlay.dart
index b769712db6..39b7e57e4b 100644
--- a/packages/flutter/lib/src/widgets/overlay.dart
+++ b/packages/flutter/lib/src/widgets/overlay.dart
@@ -508,10 +508,10 @@ class _TheatreElement extends RenderObjectElement {
       super(widget);
 
   @override
-  _Theatre get widget => super.widget;
+  _Theatre get widget => super.widget as _Theatre;
 
   @override
-  _RenderTheatre get renderObject => super.renderObject;
+  _RenderTheatre get renderObject => super.renderObject as _RenderTheatre;
 
   Element _onstage;
   static final Object _onstageSlot = Object();
@@ -524,10 +524,10 @@ class _TheatreElement extends RenderObjectElement {
     assert(renderObject.debugValidateChild(child));
     if (slot == _onstageSlot) {
       assert(child is RenderStack);
-      renderObject.child = child;
+      renderObject.child = child as RenderStack;
     } else {
       assert(slot == null || slot is Element);
-      renderObject.insert(child, after: slot?.renderObject);
+      renderObject.insert(child, after: slot?.renderObject as RenderBox);
     }
   }
 
@@ -536,14 +536,14 @@ class _TheatreElement extends RenderObjectElement {
     if (slot == _onstageSlot) {
       renderObject.remove(child);
       assert(child is RenderStack);
-      renderObject.child = child;
+      renderObject.child = child as RenderStack;
     } else {
       assert(slot == null || slot is Element);
       if (renderObject.child == child) {
         renderObject.child = null;
-        renderObject.insert(child, after: slot?.renderObject);
+        renderObject.insert(child, after: slot?.renderObject as RenderBox);
       } else {
-        renderObject.move(child, after: slot?.renderObject);
+        renderObject.move(child, after: slot?.renderObject as RenderBox);
       }
     }
   }
@@ -675,7 +675,7 @@ class _RenderTheatre extends RenderBox
         );
         if (child == lastChild)
           break;
-        final StackParentData childParentData = child.parentData;
+        final StackParentData childParentData = child.parentData as StackParentData;
         child = childParentData.nextSibling;
         count += 1;
       }
diff --git a/packages/flutter/lib/src/widgets/overscroll_indicator.dart b/packages/flutter/lib/src/widgets/overscroll_indicator.dart
index 9aac078ca1..ec610e50f1 100644
--- a/packages/flutter/lib/src/widgets/overscroll_indicator.dart
+++ b/packages/flutter/lib/src/widgets/overscroll_indicator.dart
@@ -183,17 +183,17 @@ class _GlowingOverscrollIndicatorState extends State<GlowingOverscrollIndicator>
           assert(notification.overscroll != 0.0);
           if (notification.dragDetails != null) {
             assert(notification.dragDetails.globalPosition != null);
-            final RenderBox renderer = notification.context.findRenderObject();
+            final RenderBox renderer = notification.context.findRenderObject() as RenderBox;
             assert(renderer != null);
             assert(renderer.hasSize);
             final Size size = renderer.size;
             final Offset position = renderer.globalToLocal(notification.dragDetails.globalPosition);
             switch (notification.metrics.axis) {
               case Axis.horizontal:
-                controller.pull(notification.overscroll.abs(), size.width, position.dy.clamp(0.0, size.height), size.height);
+                controller.pull(notification.overscroll.abs(), size.width, position.dy.clamp(0.0, size.height) as double, size.height);
                 break;
               case Axis.vertical:
-                controller.pull(notification.overscroll.abs(), size.height, position.dx.clamp(0.0, size.width), size.width);
+                controller.pull(notification.overscroll.abs(), size.height, position.dx.clamp(0.0, size.width) as double, size.width);
                 break;
             }
           }
@@ -335,9 +335,9 @@ class _GlowController extends ChangeNotifier {
     assert(velocity >= 0.0);
     _pullRecedeTimer?.cancel();
     _pullRecedeTimer = null;
-    velocity = velocity.clamp(_minVelocity, _maxVelocity);
+    velocity = velocity.clamp(_minVelocity, _maxVelocity) as double;
     _glowOpacityTween.begin = _state == _GlowState.idle ? 0.3 : _glowOpacity.value;
-    _glowOpacityTween.end = (velocity * _velocityGlowFactor).clamp(_glowOpacityTween.begin, _maxOpacity);
+    _glowOpacityTween.end = (velocity * _velocityGlowFactor).clamp(_glowOpacityTween.begin, _maxOpacity) as double;
     _glowSizeTween.begin = _glowSize.value;
     _glowSizeTween.end = math.min(0.025 + 7.5e-7 * velocity * velocity, 1.0);
     _glowController.duration = Duration(milliseconds: (0.15 + velocity * 0.02).round());
diff --git a/packages/flutter/lib/src/widgets/page_storage.dart b/packages/flutter/lib/src/widgets/page_storage.dart
index f39e63a37d..137c55ae6d 100644
--- a/packages/flutter/lib/src/widgets/page_storage.dart
+++ b/packages/flutter/lib/src/widgets/page_storage.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'package:flutter/foundation.dart';
+
 import 'framework.dart';
 
 /// A [ValueKey] that defines where [PageStorage] values will be saved.
@@ -48,12 +50,8 @@ class _StorageEntryIdentifier {
   bool operator ==(dynamic other) {
     if (other.runtimeType != runtimeType)
       return false;
-    final _StorageEntryIdentifier typedOther = other;
-    for (int index = 0; index < keys.length; index += 1) {
-      if (keys[index] != typedOther.keys[index])
-        return false;
-    }
-    return true;
+    return other is _StorageEntryIdentifier
+        && listEquals<PageStorageKey<dynamic>>(other.keys, keys);
   }
 
   @override
diff --git a/packages/flutter/lib/src/widgets/page_view.dart b/packages/flutter/lib/src/widgets/page_view.dart
index d6fb200c34..058fec7f54 100644
--- a/packages/flutter/lib/src/widgets/page_view.dart
+++ b/packages/flutter/lib/src/widgets/page_view.dart
@@ -184,7 +184,7 @@ class PageController extends ScrollController {
       'The page property cannot be read when multiple PageViews are attached to '
       'the same PageController.',
     );
-    final _PagePosition position = this.position;
+    final _PagePosition position = this.position as _PagePosition;
     return position.page;
   }
 
@@ -199,7 +199,7 @@ class PageController extends ScrollController {
     @required Duration duration,
     @required Curve curve,
   }) {
-    final _PagePosition position = this.position;
+    final _PagePosition position = this.position as _PagePosition;
     return position.animateTo(
       position.getPixelsFromPage(page.toDouble()),
       duration: duration,
@@ -212,7 +212,7 @@ class PageController extends ScrollController {
   /// Jumps the page position from its current value to the given value,
   /// without animation, and without checking if the new value is in range.
   void jumpToPage(int page) {
-    final _PagePosition position = this.position;
+    final _PagePosition position = this.position as _PagePosition;
     position.jumpTo(position.getPixelsFromPage(page.toDouble()));
   }
 
@@ -251,7 +251,7 @@ class PageController extends ScrollController {
   @override
   void attach(ScrollPosition position) {
     super.attach(position);
-    final _PagePosition pagePosition = position;
+    final _PagePosition pagePosition = position as _PagePosition;
     pagePosition.viewportFraction = viewportFraction;
   }
 }
@@ -372,7 +372,7 @@ class _PagePosition extends ScrollPositionWithSingleContext implements PageMetri
       pixels == null || (minScrollExtent != null && maxScrollExtent != null),
       'Page value is only available after content dimensions are established.',
     );
-    return pixels == null ? null : getPageFromPixels(pixels.clamp(minScrollExtent, maxScrollExtent), viewportDimension);
+    return pixels == null ? null : getPageFromPixels(pixels.clamp(minScrollExtent, maxScrollExtent) as double, viewportDimension);
   }
 
   @override
@@ -383,7 +383,7 @@ class _PagePosition extends ScrollPositionWithSingleContext implements PageMetri
   @override
   void restoreScrollOffset() {
     if (pixels == null) {
-      final double value = PageStorage.of(context.storageContext)?.readState(context.storageContext);
+      final double value = PageStorage.of(context.storageContext)?.readState(context.storageContext) as double;
       if (value != null)
         _pageToUseOnStartup = value;
     }
@@ -499,7 +499,7 @@ class PageScrollPhysics extends ScrollPhysics {
         (velocity >= 0.0 && position.pixels >= position.maxScrollExtent))
       return super.createBallisticSimulation(position, velocity);
     final Tolerance tolerance = this.tolerance;
-    final double target = _getTargetPixels(position, tolerance, velocity);
+    final double target = _getTargetPixels(position as ScrollPosition, tolerance, velocity);
     if (target != position.pixels)
       return ScrollSpringSimulation(spring, position.pixels, target, velocity, tolerance: tolerance);
     return null;
@@ -806,7 +806,7 @@ class _PageViewState extends State<PageView> {
     return NotificationListener<ScrollNotification>(
       onNotification: (ScrollNotification notification) {
         if (notification.depth == 0 && widget.onPageChanged != null && notification is ScrollUpdateNotification) {
-          final PageMetrics metrics = notification.metrics;
+          final PageMetrics metrics = notification.metrics as PageMetrics;
           final int currentPage = metrics.page.round();
           if (currentPage != _lastReportedPage) {
             _lastReportedPage = currentPage;
diff --git a/packages/flutter/lib/src/widgets/routes.dart b/packages/flutter/lib/src/widgets/routes.dart
index 7e567d19f8..850b30b8da 100644
--- a/packages/flutter/lib/src/widgets/routes.dart
+++ b/packages/flutter/lib/src/widgets/routes.dart
@@ -763,7 +763,7 @@ abstract class ModalRoute<T> extends TransitionRoute<T> with LocalHistoryRoute<T
   @optionalTypeArgs
   static ModalRoute<T> of<T extends Object>(BuildContext context) {
     final _ModalScopeStatus widget = context.dependOnInheritedWidgetOfExactType<_ModalScopeStatus>();
-    return widget?.route;
+    return widget?.route as ModalRoute<T>;
   }
 
   /// Schedule a call to [buildTransitions].
diff --git a/packages/flutter/lib/src/widgets/scroll_activity.dart b/packages/flutter/lib/src/widgets/scroll_activity.dart
index 78a9743980..15fcaedd44 100644
--- a/packages/flutter/lib/src/widgets/scroll_activity.dart
+++ b/packages/flutter/lib/src/widgets/scroll_activity.dart
@@ -433,21 +433,21 @@ class DragScrollActivity extends ScrollActivity {
   void dispatchScrollStartNotification(ScrollMetrics metrics, BuildContext context) {
     final dynamic lastDetails = _controller.lastDetails;
     assert(lastDetails is DragStartDetails);
-    ScrollStartNotification(metrics: metrics, context: context, dragDetails: lastDetails).dispatch(context);
+    ScrollStartNotification(metrics: metrics, context: context, dragDetails: lastDetails as DragStartDetails).dispatch(context);
   }
 
   @override
   void dispatchScrollUpdateNotification(ScrollMetrics metrics, BuildContext context, double scrollDelta) {
     final dynamic lastDetails = _controller.lastDetails;
     assert(lastDetails is DragUpdateDetails);
-    ScrollUpdateNotification(metrics: metrics, context: context, scrollDelta: scrollDelta, dragDetails: lastDetails).dispatch(context);
+    ScrollUpdateNotification(metrics: metrics, context: context, scrollDelta: scrollDelta, dragDetails: lastDetails as DragUpdateDetails).dispatch(context);
   }
 
   @override
   void dispatchOverscrollNotification(ScrollMetrics metrics, BuildContext context, double overscroll) {
     final dynamic lastDetails = _controller.lastDetails;
     assert(lastDetails is DragUpdateDetails);
-    OverscrollNotification(metrics: metrics, context: context, overscroll: overscroll, dragDetails: lastDetails).dispatch(context);
+    OverscrollNotification(metrics: metrics, context: context, overscroll: overscroll, dragDetails: lastDetails as DragUpdateDetails).dispatch(context);
   }
 
   @override
diff --git a/packages/flutter/lib/src/widgets/scroll_position.dart b/packages/flutter/lib/src/widgets/scroll_position.dart
index 49e7b3bdd8..8810de6c85 100644
--- a/packages/flutter/lib/src/widgets/scroll_position.dart
+++ b/packages/flutter/lib/src/widgets/scroll_position.dart
@@ -381,7 +381,7 @@ abstract class ScrollPosition extends ViewportOffset with ScrollMetrics {
   @protected
   void restoreScrollOffset() {
     if (pixels == null) {
-      final double value = PageStorage.of(context.storageContext)?.readState(context.storageContext);
+      final double value = PageStorage.of(context.storageContext)?.readState(context.storageContext) as double;
       if (value != null)
         correctPixels(value);
     }
@@ -543,16 +543,16 @@ abstract class ScrollPosition extends ViewportOffset with ScrollMetrics {
     double target;
     switch (alignmentPolicy) {
       case ScrollPositionAlignmentPolicy.explicit:
-        target = viewport.getOffsetToReveal(object, alignment).offset.clamp(minScrollExtent, maxScrollExtent);
+        target = viewport.getOffsetToReveal(object, alignment).offset.clamp(minScrollExtent, maxScrollExtent) as double;
         break;
       case ScrollPositionAlignmentPolicy.keepVisibleAtEnd:
-        target = viewport.getOffsetToReveal(object, 1.0).offset.clamp(minScrollExtent, maxScrollExtent);
+        target = viewport.getOffsetToReveal(object, 1.0).offset.clamp(minScrollExtent, maxScrollExtent) as double;
         if (target < pixels) {
           target = pixels;
         }
         break;
       case ScrollPositionAlignmentPolicy.keepVisibleAtStart:
-        target = viewport.getOffsetToReveal(object, 0.0).offset.clamp(minScrollExtent, maxScrollExtent);
+        target = viewport.getOffsetToReveal(object, 0.0).offset.clamp(minScrollExtent, maxScrollExtent) as double;
         if (target > pixels) {
           target = pixels;
         }
@@ -641,7 +641,7 @@ abstract class ScrollPosition extends ViewportOffset with ScrollMetrics {
     assert(clamp != null);
 
     if (clamp)
-      to = to.clamp(minScrollExtent, maxScrollExtent);
+      to = to.clamp(minScrollExtent, maxScrollExtent) as double;
 
     return super.moveTo(to, duration: duration, curve: curve);
   }
diff --git a/packages/flutter/lib/src/widgets/scroll_position_with_single_context.dart b/packages/flutter/lib/src/widgets/scroll_position_with_single_context.dart
index 572222b76d..894e6754e9 100644
--- a/packages/flutter/lib/src/widgets/scroll_position_with_single_context.dart
+++ b/packages/flutter/lib/src/widgets/scroll_position_with_single_context.dart
@@ -91,7 +91,7 @@ class ScrollPositionWithSingleContext extends ScrollPosition implements ScrollAc
       return;
     }
     activity.updateDelegate(this);
-    final ScrollPositionWithSingleContext typedOther = other;
+    final ScrollPositionWithSingleContext typedOther = other as ScrollPositionWithSingleContext;
     _userScrollDirection = typedOther._userScrollDirection;
     assert(_currentDrag == null);
     if (typedOther._currentDrag != null) {
diff --git a/packages/flutter/lib/src/widgets/scroll_simulation.dart b/packages/flutter/lib/src/widgets/scroll_simulation.dart
index dd4d0fc637..25141da0f4 100644
--- a/packages/flutter/lib/src/widgets/scroll_simulation.dart
+++ b/packages/flutter/lib/src/widgets/scroll_simulation.dart
@@ -212,13 +212,13 @@ class ClampingScrollSimulation extends Simulation {
 
   @override
   double x(double time) {
-    final double t = (time / _duration).clamp(0.0, 1.0);
+    final double t = (time / _duration).clamp(0.0, 1.0) as double;
     return position + _distance * _flingDistancePenetration(t) * velocity.sign;
   }
 
   @override
   double dx(double time) {
-    final double t = (time / _duration).clamp(0.0, 1.0);
+    final double t = (time / _duration).clamp(0.0, 1.0) as double;
     return _distance * _flingVelocityPenetration(t) * velocity.sign / _duration;
   }
 
diff --git a/packages/flutter/lib/src/widgets/scrollable.dart b/packages/flutter/lib/src/widgets/scrollable.dart
index da5125be77..193d8be22e 100644
--- a/packages/flutter/lib/src/widgets/scrollable.dart
+++ b/packages/flutter/lib/src/widgets/scrollable.dart
@@ -481,7 +481,7 @@ class ScrollableState extends State<Scrollable> with TickerProviderStateMixin
       return;
     _shouldIgnorePointer = value;
     if (_ignorePointerKey.currentContext != null) {
-      final RenderIgnorePointer renderBox = _ignorePointerKey.currentContext.findRenderObject();
+      final RenderIgnorePointer renderBox = _ignorePointerKey.currentContext.findRenderObject() as RenderIgnorePointer;
       renderBox.ignoring = _shouldIgnorePointer;
     }
   }
@@ -576,7 +576,7 @@ class ScrollableState extends State<Scrollable> with TickerProviderStateMixin
     if (_physics != null && !_physics.shouldAcceptUserOffset(position)) {
       return;
     }
-    final double targetScrollOffset = _targetScrollOffsetForPointerScroll(event);
+    final double targetScrollOffset = _targetScrollOffsetForPointerScroll(event as PointerScrollEvent);
     if (targetScrollOffset != position.pixels) {
       position.jumpTo(targetScrollOffset);
     }
diff --git a/packages/flutter/lib/src/widgets/scrollbar.dart b/packages/flutter/lib/src/widgets/scrollbar.dart
index bf997e9fe4..6a324b884f 100644
--- a/packages/flutter/lib/src/widgets/scrollbar.dart
+++ b/packages/flutter/lib/src/widgets/scrollbar.dart
@@ -240,7 +240,7 @@ class ScrollbarPainter extends ChangeNotifier implements CustomPainter {
     // isn't less than the absolute minimum size.
     // _totalContentExtent >= viewportDimension, so (_totalContentExtent - _mainAxisPadding) > 0
     final double fractionVisible = ((_lastMetrics.extentInside - _mainAxisPadding) / (_totalContentExtent - _mainAxisPadding))
-      .clamp(0.0, 1.0);
+      .clamp(0.0, 1.0) as double;
 
     final double thumbExtent = math.max(
       math.min(_trackExtent, minOverscrollLength),
@@ -267,7 +267,7 @@ class ScrollbarPainter extends ChangeNotifier implements CustomPainter {
 
     // The `thumbExtent` should be no greater than `trackSize`, otherwise
     // the scrollbar may scroll towards the wrong direction.
-    return thumbExtent.clamp(newMinLength, _trackExtent);
+    return thumbExtent.clamp(newMinLength, _trackExtent) as double;
   }
 
   @override
@@ -311,7 +311,7 @@ class ScrollbarPainter extends ChangeNotifier implements CustomPainter {
     final double scrollableExtent = metrics.maxScrollExtent - metrics.minScrollExtent;
 
     final double fractionPast = (scrollableExtent > 0)
-      ? ((metrics.pixels - metrics.minScrollExtent) / scrollableExtent).clamp(0.0, 1.0)
+      ? ((metrics.pixels - metrics.minScrollExtent) / scrollableExtent).clamp(0.0, 1.0) as double
       : 0;
 
     return (_isReversed ? 1 - fractionPast : fractionPast) * (_trackExtent - thumbExtent);
diff --git a/packages/flutter/lib/src/widgets/shortcuts.dart b/packages/flutter/lib/src/widgets/shortcuts.dart
index f96b9ef0d1..9b25b847c7 100644
--- a/packages/flutter/lib/src/widgets/shortcuts.dart
+++ b/packages/flutter/lib/src/widgets/shortcuts.dart
@@ -89,8 +89,8 @@ class KeySet<T extends KeyboardKey> extends Diagnosticable {
     if (other.runtimeType != runtimeType) {
       return false;
     }
-    final KeySet<T> typedOther = other;
-    return setEquals<T>(_keys, typedOther._keys);
+    return other is KeySet<T>
+        && setEquals<T>(other._keys, _keys);
   }
 
   @override
diff --git a/packages/flutter/lib/src/widgets/single_child_scroll_view.dart b/packages/flutter/lib/src/widgets/single_child_scroll_view.dart
index 151c696fc6..eebd797fef 100644
--- a/packages/flutter/lib/src/widgets/single_child_scroll_view.dart
+++ b/packages/flutter/lib/src/widgets/single_child_scroll_view.dart
@@ -575,7 +575,7 @@ class _RenderSingleChildViewport extends RenderBox with RenderObjectWithChildMix
     if (target is! RenderBox)
       return RevealedOffset(offset: offset.pixels, rect: rect);
 
-    final RenderBox targetBox = target;
+    final RenderBox targetBox = target as RenderBox;
     final Matrix4 transform = targetBox.getTransformTo(child);
     final Rect bounds = MatrixUtils.transformRect(transform, rect);
     final Size contentSize = child.size;
diff --git a/packages/flutter/lib/src/widgets/sliver.dart b/packages/flutter/lib/src/widgets/sliver.dart
index c2903e6003..c11ace67ab 100644
--- a/packages/flutter/lib/src/widgets/sliver.dart
+++ b/packages/flutter/lib/src/widgets/sliver.dart
@@ -815,7 +815,7 @@ class SliverList extends SliverMultiBoxAdaptorWidget {
 
   @override
   RenderSliverList createRenderObject(BuildContext context) {
-    final SliverMultiBoxAdaptorElement element = context;
+    final SliverMultiBoxAdaptorElement element = context as SliverMultiBoxAdaptorElement;
     return RenderSliverList(childManager: element);
   }
 }
@@ -878,7 +878,7 @@ class SliverFixedExtentList extends SliverMultiBoxAdaptorWidget {
 
   @override
   RenderSliverFixedExtentList createRenderObject(BuildContext context) {
-    final SliverMultiBoxAdaptorElement element = context;
+    final SliverMultiBoxAdaptorElement element = context as SliverMultiBoxAdaptorElement;
     return RenderSliverFixedExtentList(childManager: element, itemExtent: itemExtent);
   }
 
@@ -998,7 +998,7 @@ class SliverGrid extends SliverMultiBoxAdaptorWidget {
 
   @override
   RenderSliverGrid createRenderObject(BuildContext context) {
-    final SliverMultiBoxAdaptorElement element = context;
+    final SliverMultiBoxAdaptorElement element = context as SliverMultiBoxAdaptorElement;
     return RenderSliverGrid(childManager: element, gridDelegate: gridDelegate);
   }
 
@@ -1085,7 +1085,7 @@ class _SliverFillViewportRenderObjectWidget extends SliverMultiBoxAdaptorWidget
 
   @override
   RenderSliverFillViewport createRenderObject(BuildContext context) {
-    final SliverMultiBoxAdaptorElement element = context;
+    final SliverMultiBoxAdaptorElement element = context as SliverMultiBoxAdaptorElement;
     return RenderSliverFillViewport(childManager: element, viewportFraction: viewportFraction);
   }
 
@@ -1175,10 +1175,10 @@ class SliverMultiBoxAdaptorElement extends RenderObjectElement implements Render
   SliverMultiBoxAdaptorElement(SliverMultiBoxAdaptorWidget widget) : super(widget);
 
   @override
-  SliverMultiBoxAdaptorWidget get widget => super.widget;
+  SliverMultiBoxAdaptorWidget get widget => super.widget as SliverMultiBoxAdaptorWidget;
 
   @override
-  RenderSliverMultiBoxAdaptor get renderObject => super.renderObject;
+  RenderSliverMultiBoxAdaptor get renderObject => super.renderObject as RenderSliverMultiBoxAdaptor;
 
   @override
   void update(covariant SliverMultiBoxAdaptorWidget newWidget) {
@@ -1220,9 +1220,9 @@ class SliverMultiBoxAdaptorElement extends RenderObjectElement implements Render
         final Element newChild = updateChild(newChildren[index], _build(index), index);
         if (newChild != null) {
           _childElements[index] = newChild;
-          final SliverMultiBoxAdaptorParentData parentData = newChild.renderObject.parentData;
+          final SliverMultiBoxAdaptorParentData parentData = newChild.renderObject.parentData as SliverMultiBoxAdaptorParentData;
           if (!parentData.keptAlive)
-            _currentBeforeChild = newChild.renderObject;
+            _currentBeforeChild = newChild.renderObject as RenderBox;
         } else {
           _childElements.remove(index);
         }
@@ -1266,7 +1266,7 @@ class SliverMultiBoxAdaptorElement extends RenderObjectElement implements Render
     owner.buildScope(this, () {
       final bool insertFirst = after == null;
       assert(insertFirst || _childElements[index-1] != null);
-      _currentBeforeChild = insertFirst ? null : _childElements[index-1].renderObject;
+      _currentBeforeChild = insertFirst ? null : (_childElements[index-1].renderObject as RenderBox);
       Element newChild;
       try {
         _currentlyUpdatingChildIndex = index;
@@ -1284,9 +1284,9 @@ class SliverMultiBoxAdaptorElement extends RenderObjectElement implements Render
 
   @override
   Element updateChild(Element child, Widget newWidget, dynamic newSlot) {
-    final SliverMultiBoxAdaptorParentData oldParentData = child?.renderObject?.parentData;
+    final SliverMultiBoxAdaptorParentData oldParentData = child?.renderObject?.parentData as SliverMultiBoxAdaptorParentData;
     final Element newChild = super.updateChild(child, newWidget, newSlot);
-    final SliverMultiBoxAdaptorParentData newParentData = newChild?.renderObject?.parentData;
+    final SliverMultiBoxAdaptorParentData newParentData = newChild?.renderObject?.parentData as SliverMultiBoxAdaptorParentData;
 
     // Preserve the old layoutOffset if the renderObject was swapped out.
     if (oldParentData != newParentData && oldParentData != null && newParentData != null) {
@@ -1390,7 +1390,7 @@ class SliverMultiBoxAdaptorElement extends RenderObjectElement implements Render
   @override
   void didAdoptChild(RenderBox child) {
     assert(_currentlyUpdatingChildIndex != null);
-    final SliverMultiBoxAdaptorParentData childParentData = child.parentData;
+    final SliverMultiBoxAdaptorParentData childParentData = child.parentData as SliverMultiBoxAdaptorParentData;
     childParentData.index = _currentlyUpdatingChildIndex;
   }
 
@@ -1406,9 +1406,9 @@ class SliverMultiBoxAdaptorElement extends RenderObjectElement implements Render
     assert(slot != null);
     assert(_currentlyUpdatingChildIndex == slot);
     assert(renderObject.debugValidateChild(child));
-    renderObject.insert(child, after: _currentBeforeChild);
+    renderObject.insert(child as RenderBox, after: _currentBeforeChild);
     assert(() {
-      final SliverMultiBoxAdaptorParentData childParentData = child.parentData;
+      final SliverMultiBoxAdaptorParentData childParentData = child.parentData as SliverMultiBoxAdaptorParentData;
       assert(slot == childParentData.index);
       return true;
     }());
@@ -1418,13 +1418,13 @@ class SliverMultiBoxAdaptorElement extends RenderObjectElement implements Render
   void moveChildRenderObject(covariant RenderObject child, int slot) {
     assert(slot != null);
     assert(_currentlyUpdatingChildIndex == slot);
-    renderObject.move(child, after: _currentBeforeChild);
+    renderObject.move(child as RenderBox, after: _currentBeforeChild);
   }
 
   @override
   void removeChildRenderObject(covariant RenderObject child) {
     assert(_currentlyUpdatingChildIndex != null);
-    renderObject.remove(child);
+    renderObject.remove(child as RenderBox);
   }
 
   @override
@@ -1438,7 +1438,7 @@ class SliverMultiBoxAdaptorElement extends RenderObjectElement implements Render
   @override
   void debugVisitOnstageChildren(ElementVisitor visitor) {
     _childElements.values.where((Element child) {
-      final SliverMultiBoxAdaptorParentData parentData = child.renderObject.parentData;
+      final SliverMultiBoxAdaptorParentData parentData = child.renderObject.parentData as SliverMultiBoxAdaptorParentData;
       double itemExtent;
       switch (renderObject.constraints.axis) {
         case Axis.horizontal:
@@ -1936,7 +1936,7 @@ class _SliverOffstageElement extends SingleChildRenderObjectElement {
   _SliverOffstageElement(SliverOffstage widget) : super(widget);
 
   @override
-  SliverOffstage get widget => super.widget;
+  SliverOffstage get widget => super.widget as SliverOffstage;
 
   @override
   void debugVisitOnstageChildren(ElementVisitor visitor) {
@@ -1985,7 +1985,7 @@ class KeepAlive extends ParentDataWidget<SliverWithKeepAliveWidget> {
   @override
   void applyParentData(RenderObject renderObject) {
     assert(renderObject.parentData is KeepAliveParentDataMixin);
-    final KeepAliveParentDataMixin parentData = renderObject.parentData;
+    final KeepAliveParentDataMixin parentData = renderObject.parentData as KeepAliveParentDataMixin;
     if (parentData.keepAlive != keepAlive) {
       parentData.keepAlive = keepAlive;
       final AbstractNode targetParent = renderObject.parent;
diff --git a/packages/flutter/lib/src/widgets/sliver_persistent_header.dart b/packages/flutter/lib/src/widgets/sliver_persistent_header.dart
index b8a22c9a27..30467ff099 100644
--- a/packages/flutter/lib/src/widgets/sliver_persistent_header.dart
+++ b/packages/flutter/lib/src/widgets/sliver_persistent_header.dart
@@ -173,10 +173,10 @@ class _SliverPersistentHeaderElement extends RenderObjectElement {
   _SliverPersistentHeaderElement(_SliverPersistentHeaderRenderObjectWidget widget) : super(widget);
 
   @override
-  _SliverPersistentHeaderRenderObjectWidget get widget => super.widget;
+  _SliverPersistentHeaderRenderObjectWidget get widget => super.widget as _SliverPersistentHeaderRenderObjectWidget;
 
   @override
-  _RenderSliverPersistentHeaderForWidgetsMixin get renderObject => super.renderObject;
+  _RenderSliverPersistentHeaderForWidgetsMixin get renderObject => super.renderObject as _RenderSliverPersistentHeaderForWidgetsMixin;
 
   @override
   void mount(Element parent, dynamic newSlot) {
@@ -230,7 +230,7 @@ class _SliverPersistentHeaderElement extends RenderObjectElement {
   }
 
   @override
-  void insertChildRenderObject(covariant RenderObject child, dynamic slot) {
+  void insertChildRenderObject(covariant RenderBox child, dynamic slot) {
     assert(renderObject.debugValidateChild(child));
     renderObject.child = child;
   }
diff --git a/packages/flutter/lib/src/widgets/sliver_prototype_extent_list.dart b/packages/flutter/lib/src/widgets/sliver_prototype_extent_list.dart
index bbd84512d9..9afa8df265 100644
--- a/packages/flutter/lib/src/widgets/sliver_prototype_extent_list.dart
+++ b/packages/flutter/lib/src/widgets/sliver_prototype_extent_list.dart
@@ -52,7 +52,7 @@ class SliverPrototypeExtentList extends SliverMultiBoxAdaptorWidget {
 
   @override
   _RenderSliverPrototypeExtentList createRenderObject(BuildContext context) {
-    final _SliverPrototypeExtentListElement element = context;
+    final _SliverPrototypeExtentListElement element = context as _SliverPrototypeExtentListElement;
     return _RenderSliverPrototypeExtentList(childManager: element);
   }
 
@@ -64,10 +64,10 @@ class _SliverPrototypeExtentListElement extends SliverMultiBoxAdaptorElement {
   _SliverPrototypeExtentListElement(SliverPrototypeExtentList widget) : super(widget);
 
   @override
-  SliverPrototypeExtentList get widget => super.widget;
+  SliverPrototypeExtentList get widget => super.widget as SliverPrototypeExtentList;
 
   @override
-  _RenderSliverPrototypeExtentList get renderObject => super.renderObject;
+  _RenderSliverPrototypeExtentList get renderObject => super.renderObject as _RenderSliverPrototypeExtentList;
 
   Element _prototype;
   static final Object _prototypeSlot = Object();
@@ -76,9 +76,9 @@ class _SliverPrototypeExtentListElement extends SliverMultiBoxAdaptorElement {
   void insertChildRenderObject(covariant RenderObject child, covariant dynamic slot) {
     if (slot == _prototypeSlot) {
       assert(child is RenderBox);
-      renderObject.child = child;
+      renderObject.child = child as RenderBox;
     } else {
-      super.insertChildRenderObject(child, slot);
+      super.insertChildRenderObject(child, slot as int);
     }
   }
 
@@ -93,7 +93,7 @@ class _SliverPrototypeExtentListElement extends SliverMultiBoxAdaptorElement {
     if (slot == _prototypeSlot)
       assert(false); // There's only one prototype child so it cannot be moved.
     else
-      super.moveChildRenderObject(child, slot);
+      super.moveChildRenderObject(child, slot as int);
   }
 
   @override
diff --git a/packages/flutter/lib/src/widgets/table.dart b/packages/flutter/lib/src/widgets/table.dart
index 8a2a468cff..3eec4b717d 100644
--- a/packages/flutter/lib/src/widgets/table.dart
+++ b/packages/flutter/lib/src/widgets/table.dart
@@ -240,10 +240,10 @@ class _TableElement extends RenderObjectElement {
   _TableElement(Table widget) : super(widget);
 
   @override
-  Table get widget => super.widget;
+  Table get widget => super.widget as Table;
 
   @override
-  RenderTable get renderObject => super.renderObject;
+  RenderTable get renderObject => super.renderObject as RenderTable;
 
   // This class ignores the child's slot entirely.
   // Instead of doing incremental updates to the child list, it replaces the entire list each frame.
@@ -276,7 +276,7 @@ class _TableElement extends RenderObjectElement {
 
   @override
   void removeChildRenderObject(RenderObject child) {
-    final TableCellParentData childParentData = child.parentData;
+    final TableCellParentData childParentData = child.parentData as TableCellParentData;
     renderObject.setChild(childParentData.x, childParentData.y, null);
   }
 
@@ -326,7 +326,7 @@ class _TableElement extends RenderObjectElement {
       _children.isNotEmpty ? _children[0].children.length : 0,
       _children.expand<RenderBox>((_TableElementRow row) {
         return row.children.map<RenderBox>((Element child) {
-          final RenderBox box = child.renderObject;
+          final RenderBox box = child.renderObject as RenderBox;
           return box;
         });
       }).toList(),
@@ -367,7 +367,7 @@ class TableCell extends ParentDataWidget<Table> {
 
   @override
   void applyParentData(RenderObject renderObject) {
-    final TableCellParentData parentData = renderObject.parentData;
+    final TableCellParentData parentData = renderObject.parentData as TableCellParentData;
     if (parentData.verticalAlignment != verticalAlignment) {
       parentData.verticalAlignment = verticalAlignment;
       final AbstractNode targetParent = renderObject.parent;
diff --git a/packages/flutter/lib/src/widgets/text.dart b/packages/flutter/lib/src/widgets/text.dart
index 0640c8e431..3afbbfcfc4 100644
--- a/packages/flutter/lib/src/widgets/text.dart
+++ b/packages/flutter/lib/src/widgets/text.dart
@@ -435,7 +435,7 @@ class Text extends StatelessWidget {
       text: TextSpan(
         style: effectiveTextStyle,
         text: data,
-        children: textSpan != null ? <TextSpan>[textSpan] : null,
+        children: textSpan != null ? <InlineSpan>[textSpan] : null,
       ),
     );
     if (semanticsLabel != null) {
diff --git a/packages/flutter/lib/src/widgets/transitions.dart b/packages/flutter/lib/src/widgets/transitions.dart
index e9d9d28e83..8a0cb9729b 100644
--- a/packages/flutter/lib/src/widgets/transitions.dart
+++ b/packages/flutter/lib/src/widgets/transitions.dart
@@ -265,7 +265,7 @@ class SlideTransition extends AnimatedWidget {
   /// If the current value of the position animation is `(dx, dy)`, the child
   /// will be translated horizontally by `width * dx` and vertically by
   /// `height * dy`, after applying the [textDirection] if available.
-  Animation<Offset> get position => listenable;
+  Animation<Offset> get position => listenable as Animation<Offset>;
 
   /// The direction to use for the x offset described by the [position].
   ///
@@ -337,7 +337,7 @@ class ScaleTransition extends AnimatedWidget {
   ///
   /// If the current value of the scale animation is v, the child will be
   /// painted v times its normal size.
-  Animation<double> get scale => listenable;
+  Animation<double> get scale => listenable as Animation<double>;
 
   /// The alignment of the origin of the coordinate system in which the scale
   /// takes place, relative to the size of the box.
@@ -391,7 +391,7 @@ class RotationTransition extends AnimatedWidget {
   ///
   /// If the current value of the turns animation is v, the child will be
   /// rotated v * 2 * pi radians before being painted.
-  Animation<double> get turns => listenable;
+  Animation<double> get turns => listenable as Animation<double>;
 
   /// The alignment of the origin of the coordinate system around which the
   /// rotation occurs, relative to the size of the box.
@@ -473,7 +473,7 @@ class SizeTransition extends AnimatedWidget {
   ///
   /// If the value of [sizeFactor] is less than one, the child will be clipped
   /// in the appropriate axis.
-  Animation<double> get sizeFactor => listenable;
+  Animation<double> get sizeFactor => listenable as Animation<double>;
 
   /// Describes how to align the child along the axis that [sizeFactor] is
   /// modifying.
@@ -635,7 +635,7 @@ class PositionedTransition extends AnimatedWidget {
        super(key: key, listenable: rect);
 
   /// The animation that controls the child's size and position.
-  Animation<RelativeRect> get rect => listenable;
+  Animation<RelativeRect> get rect => listenable as Animation<RelativeRect>;
 
   /// The widget below this widget in the tree.
   ///
@@ -692,7 +692,7 @@ class RelativePositionedTransition extends AnimatedWidget {
   /// The animation that controls the child's size and position.
   ///
   /// See also [size].
-  Animation<Rect> get rect => listenable;
+  Animation<Rect> get rect => listenable as Animation<Rect>;
 
   /// The [Positioned] widget's offsets are relative to a box of this
   /// size whose origin is 0,0.
@@ -806,7 +806,7 @@ class AlignTransition extends AnimatedWidget {
        super(key: key, listenable: alignment);
 
   /// The animation that controls the child's alignment.
-  Animation<AlignmentGeometry> get alignment => listenable;
+  Animation<AlignmentGeometry> get alignment => listenable as Animation<AlignmentGeometry>;
 
   /// If non-null, the child's width factor, see [Align.widthFactor].
   final double widthFactor;
@@ -855,7 +855,7 @@ class DefaultTextStyleTransition extends AnimatedWidget {
        super(key: key, listenable: style);
 
   /// The animation that controls the descendants' text style.
-  Animation<TextStyle> get style => listenable;
+  Animation<TextStyle> get style => listenable as Animation<TextStyle>;
 
   /// How the text should be aligned horizontally.
   final TextAlign textAlign;
diff --git a/packages/flutter/lib/src/widgets/tween_animation_builder.dart b/packages/flutter/lib/src/widgets/tween_animation_builder.dart
index a4d1e9b481..d67597675c 100644
--- a/packages/flutter/lib/src/widgets/tween_animation_builder.dart
+++ b/packages/flutter/lib/src/widgets/tween_animation_builder.dart
@@ -215,7 +215,7 @@ class _TweenAnimationBuilderState<T> extends AnimatedWidgetBaseState<TweenAnimat
       // Constructor will never be called because null is never provided as current tween.
       assert(false);
       return null;
-    });
+    }) as Tween<T>;
   }
 
   @override
diff --git a/packages/flutter/lib/src/widgets/unique_widget.dart b/packages/flutter/lib/src/widgets/unique_widget.dart
index 42aeb9de35..d2d283fee7 100644
--- a/packages/flutter/lib/src/widgets/unique_widget.dart
+++ b/packages/flutter/lib/src/widgets/unique_widget.dart
@@ -34,7 +34,7 @@ abstract class UniqueWidget<T extends State<StatefulWidget>> extends StatefulWid
   ///
   /// Might be null if the widget is not currently in the tree.
   T get currentState {
-    final GlobalKey<T> globalKey = key;
+    final GlobalKey<T> globalKey = key as GlobalKey<T>;
     return globalKey.currentState;
   }
 }
diff --git a/packages/flutter/lib/src/widgets/viewport.dart b/packages/flutter/lib/src/widgets/viewport.dart
index d884d7a9fc..2623ad2a01 100644
--- a/packages/flutter/lib/src/widgets/viewport.dart
+++ b/packages/flutter/lib/src/widgets/viewport.dart
@@ -186,10 +186,10 @@ class _ViewportElement extends MultiChildRenderObjectElement {
   _ViewportElement(Viewport widget) : super(widget);
 
   @override
-  Viewport get widget => super.widget;
+  Viewport get widget => super.widget as Viewport;
 
   @override
-  RenderViewport get renderObject => super.renderObject;
+  RenderViewport get renderObject => super.renderObject as RenderViewport;
 
   @override
   void mount(Element parent, dynamic newSlot) {
@@ -208,9 +208,9 @@ class _ViewportElement extends MultiChildRenderObjectElement {
     if (widget.center != null) {
       renderObject.center = children.singleWhere(
         (Element element) => element.widget.key == widget.center
-      ).renderObject;
+      ).renderObject as RenderSliver;
     } else if (children.isNotEmpty) {
-      renderObject.center = children.first.renderObject;
+      renderObject.center = children.first.renderObject as RenderSliver;
     } else {
       renderObject.center = null;
     }
@@ -219,7 +219,7 @@ class _ViewportElement extends MultiChildRenderObjectElement {
   @override
   void debugVisitOnstageChildren(ElementVisitor visitor) {
     children.where((Element e) {
-      final RenderSliver renderSliver = e.renderObject;
+      final RenderSliver renderSliver = e.renderObject as RenderSliver;
       return renderSliver.geometry.visible;
     }).forEach(visitor);
   }
diff --git a/packages/flutter/lib/src/widgets/widget_inspector.dart b/packages/flutter/lib/src/widgets/widget_inspector.dart
index eb7adcd430..cff08a15a8 100644
--- a/packages/flutter/lib/src/widgets/widget_inspector.dart
+++ b/packages/flutter/lib/src/widgets/widget_inspector.dart
@@ -544,7 +544,7 @@ class _ScreenshotPaintingContext extends PaintingContext {
   }) {
     RenderObject repaintBoundary = renderObject;
     while (repaintBoundary != null && !repaintBoundary.isRepaintBoundary) {
-      repaintBoundary = repaintBoundary.parent;
+      repaintBoundary = repaintBoundary.parent as RenderObject;
     }
     assert(repaintBoundary != null);
     final _ScreenshotData data = _ScreenshotData(target: renderObject);
@@ -560,7 +560,7 @@ class _ScreenshotPaintingContext extends PaintingContext {
       // want to capture debugPaint information as well.
       data.containerLayer.append(_ProxyLayer(repaintBoundary.debugLayer));
       data.foundTarget = true;
-      final OffsetLayer offsetLayer = repaintBoundary.debugLayer;
+      final OffsetLayer offsetLayer = repaintBoundary.debugLayer as OffsetLayer;
       data.screenshotOffset = offsetLayer.offset;
     } else {
       // Repaint everything under the repaint boundary.
@@ -1288,10 +1288,10 @@ mixin WidgetInspectorService {
   /// The local project directories are used to distinguish widgets created by
   /// the local project over widgets created from inside the framework.
   @protected
-  void setPubRootDirectories(List<Object> pubRootDirectories) {
-    _pubRootDirectories = pubRootDirectories.map<String>(
-      (Object directory) => Uri.parse(directory).path,
-    ).toList();
+  void setPubRootDirectories(List<String> pubRootDirectories) {
+    _pubRootDirectories = pubRootDirectories
+      .map<String>((String directory) => Uri.parse(directory).path)
+      .toList();
   }
 
   /// Set the [WidgetInspector] selection to the object matching the specified
@@ -1326,7 +1326,7 @@ mixin WidgetInspectorService {
         if (object == selection.current) {
           return false;
         }
-        selection.current = object;
+        selection.current = object as RenderObject;
         developer.inspect(selection.current);
       }
       if (selectionChangedCallback != null) {
@@ -1408,7 +1408,7 @@ mixin WidgetInspectorService {
     final List<RenderObject> chain = <RenderObject>[];
     while (renderObject != null) {
       chain.add(renderObject);
-      renderObject = renderObject.parent;
+      renderObject = renderObject.parent as RenderObject;
     }
     return _followDiagnosticableChain(chain.reversed.toList());
   }
@@ -1475,7 +1475,7 @@ mixin WidgetInspectorService {
   }
 
   List<Map<String, Object>> _nodesToJson(
-    Iterable<DiagnosticsNode> nodes,
+    List<DiagnosticsNode> nodes,
     InspectorSerializationDelegate delegate, {
     @required DiagnosticsNode parent,
   }) {
@@ -1490,7 +1490,7 @@ mixin WidgetInspectorService {
   }
 
   List<Object> _getProperties(String diagnosticsNodeId, String groupName) {
-    final DiagnosticsNode node = toObject(diagnosticsNodeId);
+    final DiagnosticsNode node = toObject(diagnosticsNodeId) as DiagnosticsNode;
     return _nodesToJson(node == null ? const <DiagnosticsNode>[] : node.getProperties(), InspectorSerializationDelegate(groupName: groupName, service: this), parent: node);
   }
 
@@ -1501,7 +1501,7 @@ mixin WidgetInspectorService {
   }
 
   List<Object> _getChildren(String diagnosticsNodeId, String groupName) {
-    final DiagnosticsNode node = toObject(diagnosticsNodeId);
+    final DiagnosticsNode node = toObject(diagnosticsNodeId) as DiagnosticsNode;
     final InspectorSerializationDelegate delegate = InspectorSerializationDelegate(groupName: groupName, service: this);
     return _nodesToJson(node == null ? const <DiagnosticsNode>[] : _getChildrenFiltered(node, delegate), delegate, parent: node);
   }
@@ -1523,7 +1523,7 @@ mixin WidgetInspectorService {
   }
 
   List<Object> _getChildrenSummaryTree(String diagnosticsNodeId, String groupName) {
-    final DiagnosticsNode node = toObject(diagnosticsNodeId);
+    final DiagnosticsNode node = toObject(diagnosticsNodeId) as DiagnosticsNode;
     final InspectorSerializationDelegate delegate = InspectorSerializationDelegate(groupName: groupName, summaryTree: true, service: this);
     return _nodesToJson(node == null ? const <DiagnosticsNode>[] : _getChildrenFiltered(node, delegate), delegate, parent: node);
   }
@@ -1539,7 +1539,7 @@ mixin WidgetInspectorService {
   }
 
   List<Object> _getChildrenDetailsSubtree(String diagnosticsNodeId, String groupName) {
-    final DiagnosticsNode node = toObject(diagnosticsNodeId);
+    final DiagnosticsNode node = toObject(diagnosticsNodeId) as DiagnosticsNode;
     // With this value of minDepth we only expand one extra level of important nodes.
     final InspectorSerializationDelegate delegate = InspectorSerializationDelegate(groupName: groupName, subtreeDepth: 1, includeProperties: true, service: this);
     return _nodesToJson(node == null ? const <DiagnosticsNode>[] : _getChildrenFiltered(node, delegate), delegate, parent: node);
@@ -1641,7 +1641,7 @@ mixin WidgetInspectorService {
     String groupName,
     int subtreeDepth,
   ) {
-    final DiagnosticsNode root = toObject(id);
+    final DiagnosticsNode root = toObject(id) as DiagnosticsNode;
     if (root == null) {
       return null;
     }
@@ -1669,7 +1669,7 @@ mixin WidgetInspectorService {
   }
 
   Map<String, Object> _getSelectedRenderObject(String previousSelectionId, String groupName) {
-    final DiagnosticsNode previousSelection = toObject(previousSelectionId);
+    final DiagnosticsNode previousSelection = toObject(previousSelectionId) as DiagnosticsNode;
     final RenderObject current = selection?.current;
     return _nodeToJson(current == previousSelection?.value ? previousSelection : current?.toDiagnosticsNode(), InspectorSerializationDelegate(groupName: groupName, service: this));
   }
@@ -1708,7 +1708,7 @@ mixin WidgetInspectorService {
     if (object is! Element && object is! RenderObject) {
       return null;
     }
-    final RenderObject renderObject = object is Element ? object.renderObject : object;
+    final RenderObject renderObject = object is Element ? object.renderObject : (object as RenderObject);
     if (renderObject == null || !renderObject.attached) {
       return null;
     }
@@ -1756,7 +1756,7 @@ mixin WidgetInspectorService {
   }
 
   Map<String, Object> _getSelectedWidget(String previousSelectionId, String groupName) {
-    final DiagnosticsNode previousSelection = toObject(previousSelectionId);
+    final DiagnosticsNode previousSelection = toObject(previousSelectionId) as DiagnosticsNode;
     final Element current = selection?.currentElement;
     return _nodeToJson(current == previousSelection?.value ? previousSelection : current?.toDiagnosticsNode(), InspectorSerializationDelegate(groupName: groupName, service: this));
   }
@@ -1777,7 +1777,7 @@ mixin WidgetInspectorService {
     if (!isWidgetCreationTracked()) {
       return _getSelectedWidget(previousSelectionId, groupName);
     }
-    final DiagnosticsNode previousSelection = toObject(previousSelectionId);
+    final DiagnosticsNode previousSelection = toObject(previousSelectionId) as DiagnosticsNode;
     Element current = selection?.currentElement;
     if (current != null && !_isValueCreatedByLocalProject(current)) {
       Element firstLocal;
@@ -1843,7 +1843,7 @@ mixin WidgetInspectorService {
 
   void _onPaint(RenderObject renderObject) {
     try {
-      final Element element = renderObject.debugCreator?.element;
+      final Element element = renderObject.debugCreator?.element as Element;
       if (element is! RenderObjectElement) {
         // This branch should not hit as long as all RenderObjects were created
         // by Widgets. It is possible there might be some render objects
@@ -1958,7 +1958,7 @@ class _ElementLocationStatsTracker {
     if (widget is! _HasCreationLocation) {
       return;
     }
-    final _HasCreationLocation creationLocationSource = widget;
+    final _HasCreationLocation creationLocationSource = widget as _HasCreationLocation;
     final _Location location = creationLocationSource._location;
     final int id = _toLocationId(location);
 
@@ -2161,7 +2161,7 @@ class _WidgetInspectorState extends State<WidgetInspector>
       if (diagnostics.style == DiagnosticsTreeStyle.offstage ||
           diagnostics.value is! RenderObject)
         continue;
-      final RenderObject child = diagnostics.value;
+      final RenderObject child = diagnostics.value as RenderObject;
       final Rect paintClip = object.describeApproximatePaintClip(child);
       if (paintClip != null && !paintClip.contains(localPosition))
         continue;
@@ -2215,7 +2215,7 @@ class _WidgetInspectorState extends State<WidgetInspector>
     if (!isSelectMode)
       return;
 
-    final RenderIgnorePointer ignorePointer = _ignorePointerKey.currentContext.findRenderObject();
+    final RenderIgnorePointer ignorePointer = _ignorePointerKey.currentContext.findRenderObject() as RenderIgnorePointer;
     final RenderObject userRender = ignorePointer.child;
     final List<RenderObject> selected = hitTest(position, userRender);
 
@@ -2338,7 +2338,7 @@ class InspectorSelection {
   set current(RenderObject value) {
     if (_current != value) {
       _current = value;
-      _currentElement = value.debugCreator.element;
+      _currentElement = value.debugCreator.element as Element;
     }
   }
 
@@ -2359,7 +2359,7 @@ class InspectorSelection {
   void _computeCurrent() {
     if (_index < candidates.length) {
       _current = candidates[index];
-      _currentElement = _current.debugCreator.element;
+      _currentElement = _current.debugCreator.element as Element;
     } else {
       _current = null;
       _currentElement = null;
@@ -2438,8 +2438,9 @@ class _TransformedRect {
   bool operator ==(dynamic other) {
     if (other.runtimeType != runtimeType)
       return false;
-    final _TransformedRect typedOther = other;
-    return rect == typedOther.rect && transform == typedOther.transform;
+    return other is _TransformedRect
+        && other.rect == rect
+        && other.transform == transform;
   }
 
   @override
@@ -2469,12 +2470,11 @@ class _InspectorOverlayRenderState {
   bool operator ==(dynamic other) {
     if (other.runtimeType != runtimeType)
       return false;
-
-    final _InspectorOverlayRenderState typedOther = other;
-    return overlayRect == typedOther.overlayRect
-        && selected == typedOther.selected
-        && listEquals<_TransformedRect>(candidates, typedOther.candidates)
-        && tooltip == typedOther.tooltip;
+    return other is _InspectorOverlayRenderState
+        && other.overlayRect == overlayRect
+        && other.selected == selected
+        && listEquals<_TransformedRect>(other.candidates, candidates)
+        && other.tooltip == tooltip;
   }
 
   @override
@@ -2616,7 +2616,7 @@ class _InspectorOverlayLayer extends Layer {
   ) {
     canvas.save();
     final double maxWidth = size.width - 2 * (_kScreenEdgeMargin + _kTooltipPadding);
-    final TextSpan textSpan = _textPainter?.text;
+    final TextSpan textSpan = _textPainter?.text as TextSpan;
     if (_textPainter == null || textSpan.text != message || _textPainterMaxWidth != maxWidth) {
       _textPainterMaxWidth = maxWidth;
       _textPainter = TextPainter()
@@ -2789,7 +2789,7 @@ Iterable<DiagnosticsNode> transformDebugCreator(Iterable<DiagnosticsNode> proper
 Iterable<DiagnosticsNode> _parseDiagnosticsNode(DiagnosticsNode node) {
   if (!_isDebugCreator(node))
     return null;
-  final DebugCreator debugCreator = node.value;
+  final DebugCreator debugCreator = node.value as DebugCreator;
   final Element element = debugCreator.element;
   return _describeRelevantUserCode(element);
 }
diff --git a/packages/flutter/lib/src/widgets/widget_span.dart b/packages/flutter/lib/src/widgets/widget_span.dart
index 1e4cb6a7c6..65a283ef8f 100644
--- a/packages/flutter/lib/src/widgets/widget_span.dart
+++ b/packages/flutter/lib/src/widgets/widget_span.dart
@@ -148,7 +148,7 @@ class WidgetSpan extends PlaceholderSpan {
       return RenderComparison.layout;
     if ((style == null) != (other.style == null))
       return RenderComparison.layout;
-    final WidgetSpan typedOther = other;
+    final WidgetSpan typedOther = other as WidgetSpan;
     if (child != typedOther.child || alignment != typedOther.alignment) {
       return RenderComparison.layout;
     }
@@ -171,10 +171,10 @@ class WidgetSpan extends PlaceholderSpan {
       return false;
     if (super != other)
       return false;
-    final WidgetSpan typedOther = other;
-    return typedOther.child == child
-        && typedOther.alignment == alignment
-        && typedOther.baseline == baseline;
+    return other is WidgetSpan
+        && other.child == child
+        && other.alignment == alignment
+        && other.baseline == baseline;
   }
 
   @override
diff --git a/packages/flutter/test/widgets/widget_inspector_test.dart b/packages/flutter/test/widgets/widget_inspector_test.dart
index 76f4f4a545..3b468da47b 100644
--- a/packages/flutter/test/widgets/widget_inspector_test.dart
+++ b/packages/flutter/test/widgets/widget_inspector_test.dart
@@ -810,7 +810,7 @@ class TestWidgetInspectorService extends Object with WidgetInspectorService {
       final Element elementB = find.text('b').evaluate().first;
 
       service.disposeAllGroups();
-      service.setPubRootDirectories(<Object>[]);
+      service.setPubRootDirectories(<String>[]);
       service.setSelection(elementA, 'my-group');
       final Map<String, Object> jsonA = json.decode(service.getSelectedWidget(null, 'my-group'));
       final Map<String, Object> creationLocationA = jsonA['creationLocation'];
@@ -885,7 +885,7 @@ class TestWidgetInspectorService extends Object with WidgetInspectorService {
         // directory.
         pubRootTest = '/' +
           segments.take(segments.length - 2).join('/');
-        service.setPubRootDirectories(<Object>[pubRootTest]);
+        service.setPubRootDirectories(<String>[pubRootTest]);
       }
       final DiagnosticPropertiesBuilder builder = DiagnosticPropertiesBuilder();
       builder.add(StringProperty('dummy1', 'value'));
@@ -948,7 +948,7 @@ class TestWidgetInspectorService extends Object with WidgetInspectorService {
         // directory.
         pubRootTest = '/' +
           segments.take(segments.length - 2).join('/');
-        service.setPubRootDirectories(<Object>[pubRootTest]);
+        service.setPubRootDirectories(<String>[pubRootTest]);
       }
       final DiagnosticPropertiesBuilder builder = DiagnosticPropertiesBuilder();
       builder.add(StringProperty('dummy1', 'value'));
@@ -995,7 +995,7 @@ class TestWidgetInspectorService extends Object with WidgetInspectorService {
       final Element elementA = find.text('a').evaluate().first;
 
       service.disposeAllGroups();
-      service.setPubRootDirectories(<Object>[]);
+      service.setPubRootDirectories(<String>[]);
       service.setSelection(elementA, 'my-group');
       Map<String, Object> jsonObject = json.decode(service.getSelectedWidget(null, 'my-group'));
       Map<String, Object> creationLocation = jsonObject['creationLocation'];
@@ -1007,21 +1007,21 @@ class TestWidgetInspectorService extends Object with WidgetInspectorService {
       // Strip a couple subdirectories away to generate a plausible pub root
       // directory.
       final String pubRootTest = '/' + segments.take(segments.length - 2).join('/');
-      service.setPubRootDirectories(<Object>[pubRootTest]);
+      service.setPubRootDirectories(<String>[pubRootTest]);
 
       service.setSelection(elementA, 'my-group');
       expect(json.decode(service.getSelectedWidget(null, 'my-group')), contains('createdByLocalProject'));
 
-      service.setPubRootDirectories(<Object>['/invalid/$pubRootTest']);
+      service.setPubRootDirectories(<String>['/invalid/$pubRootTest']);
       expect(json.decode(service.getSelectedWidget(null, 'my-group')), isNot(contains('createdByLocalProject')));
 
-      service.setPubRootDirectories(<Object>['file://$pubRootTest']);
+      service.setPubRootDirectories(<String>['file://$pubRootTest']);
       expect(json.decode(service.getSelectedWidget(null, 'my-group')), contains('createdByLocalProject'));
 
-      service.setPubRootDirectories(<Object>['$pubRootTest/different']);
+      service.setPubRootDirectories(<String>['$pubRootTest/different']);
       expect(json.decode(service.getSelectedWidget(null, 'my-group')), isNot(contains('createdByLocalProject')));
 
-      service.setPubRootDirectories(<Object>[
+      service.setPubRootDirectories(<String>[
         '/invalid/$pubRootTest',
         pubRootTest,
       ]);
@@ -1034,7 +1034,7 @@ class TestWidgetInspectorService extends Object with WidgetInspectorService {
         matching: find.byType(RichText),
       ).evaluate().first;
       service.setSelection(richText, 'my-group');
-      service.setPubRootDirectories(<Object>[pubRootTest]);
+      service.setPubRootDirectories(<String>[pubRootTest]);
       jsonObject = json.decode(service.getSelectedWidget(null, 'my-group'));
       expect(jsonObject, isNot(contains('createdByLocalProject')));
       creationLocation = jsonObject['creationLocation'];
@@ -1046,12 +1046,12 @@ class TestWidgetInspectorService extends Object with WidgetInspectorService {
 
       // Strip off /src/widgets/text.dart.
       final String pubRootFramework = '/' + pathSegmentsFramework.take(pathSegmentsFramework.length - 3).join('/');
-      service.setPubRootDirectories(<Object>[pubRootFramework]);
+      service.setPubRootDirectories(<String>[pubRootFramework]);
       expect(json.decode(service.getSelectedWidget(null, 'my-group')), contains('createdByLocalProject'));
       service.setSelection(elementA, 'my-group');
       expect(json.decode(service.getSelectedWidget(null, 'my-group')), isNot(contains('createdByLocalProject')));
 
-      service.setPubRootDirectories(<Object>[pubRootFramework, pubRootTest]);
+      service.setPubRootDirectories(<String>[pubRootFramework, pubRootTest]);
       service.setSelection(elementA, 'my-group');
       expect(json.decode(service.getSelectedWidget(null, 'my-group')), contains('createdByLocalProject'));
       service.setSelection(richText, 'my-group');
@@ -1609,7 +1609,7 @@ class TestWidgetInspectorService extends Object with WidgetInspectorService {
         matching: find.byType(RichText),
       ).evaluate().first;
       service.setSelection(richText, 'my-group');
-      service.setPubRootDirectories(<Object>[pubRootTest]);
+      service.setPubRootDirectories(<String>[pubRootTest]);
       jsonObject = json.decode(service.getSelectedWidget(null, 'my-group'));
       expect(jsonObject, isNot(contains('createdByLocalProject')));
       creationLocation = jsonObject['creationLocation'];