Implementing switch expressions: everything in flutter/lib/src/ (#143634)

This PR is the 9�ʰ step in the journey to solve issue #136139 and make the entire Flutter repo more readable.

(previous pull requests: #139048, #139882, #141591, #142279, #142634, #142793, #143293, #143496)

I did a pass through all of `packages/flutter/lib/src/` and found an abundance of `switch` statements to improve. Whereas #143496 focused on in-depth refactoring, this PR is full of simple, straightforward changes. (I ended up making some more complicated changes in `rendering/` and will file those separately after this PR is done.)

Author: nate-thegrate

packages/flutter/lib/src/animation/animation_controller.dart

@@ -598,20 +598,15 @@ class AnimationController extends Animation<double>
   }
 
   TickerFuture _animateToInternal(double target, { Duration? duration, Curve curve = Curves.linear }) {
-    double scale = 1.0;
-    if (SemanticsBinding.instance.disableAnimations) {
-      switch (animationBehavior) {
-        case AnimationBehavior.normal:
-          // Since the framework cannot handle zero duration animations, we run it at 5% of the normal
-          // duration to limit most animations to a single frame.
-          // Ideally, the framework would be able to handle zero duration animations, however, the common
-          // pattern of an eternally repeating animation might cause an endless loop if it weren't delayed
-          // for at least one frame.
-          scale = 0.05;
-        case AnimationBehavior.preserve:
-          break;
-      }
-    }
+    final double scale = switch (animationBehavior) {
+      // Since the framework cannot handle zero duration animations, we run it at 5% of the normal
+      // duration to limit most animations to a single frame.
+      // Ideally, the framework would be able to handle zero duration animations, however, the common
+      // pattern of an eternally repeating animation might cause an endless loop if it weren't delayed
+      // for at least one frame.
+      AnimationBehavior.normal when SemanticsBinding.instance.disableAnimations => 0.05,
+      AnimationBehavior.normal || AnimationBehavior.preserve => 1.0,
+    };
     Duration? simulationDuration = duration;
     if (simulationDuration == null) {
       assert(!(this.duration == null && _direction == _AnimationDirection.forward));
@@ -721,16 +716,12 @@ class AnimationController extends Animation<double>
     _direction = velocity < 0.0 ? _AnimationDirection.reverse : _AnimationDirection.forward;
     final double target = velocity < 0.0 ? lowerBound - _kFlingTolerance.distance
                                          : upperBound + _kFlingTolerance.distance;
-    double scale = 1.0;
     final AnimationBehavior behavior = animationBehavior ?? this.animationBehavior;
-    if (SemanticsBinding.instance.disableAnimations) {
-      switch (behavior) {
-        case AnimationBehavior.normal:
-          scale = 200.0; // This is arbitrary (it was chosen because it worked for the drawer widget).
-        case AnimationBehavior.preserve:
-          break;
-      }
-    }
+    final double scale = switch (behavior) {
+      // This is arbitrary (it was chosen because it worked for the drawer widget).
+      AnimationBehavior.normal when SemanticsBinding.instance.disableAnimations => 200.0,
+      AnimationBehavior.normal || AnimationBehavior.preserve => 1.0,
+    };
     final SpringSimulation simulation = SpringSimulation(springDescription, value, target, velocity * scale)
       ..tolerance = _kFlingTolerance;
     assert(

packages/flutter/lib/src/animation/animations.dart

@@ -425,15 +425,10 @@ class CurvedAnimation extends Animation<double> with AnimationWithParentMixin<do
   bool isDisposed = false;
 
   void _updateCurveDirection(AnimationStatus status) {
-    switch (status) {
-      case AnimationStatus.dismissed:
-      case AnimationStatus.completed:
-        _curveDirection = null;
-      case AnimationStatus.forward:
-        _curveDirection ??= AnimationStatus.forward;
-      case AnimationStatus.reverse:
-        _curveDirection ??= AnimationStatus.reverse;
-    }
+    _curveDirection = switch (status) {
+      AnimationStatus.dismissed || AnimationStatus.completed => null,
+      AnimationStatus.forward || AnimationStatus.reverse => _curveDirection ?? status,
+    };
   }
 
   bool get _useForwardCurve {
@@ -584,12 +579,10 @@ class TrainHoppingAnimation extends Animation<double>
     bool hop = false;
     if (_nextTrain != null) {
       assert(_mode != null);
-      switch (_mode!) {
-        case _TrainHoppingMode.minimize:
-          hop = _nextTrain!.value <= _currentTrain!.value;
-        case _TrainHoppingMode.maximize:
-          hop = _nextTrain!.value >= _currentTrain!.value;
-      }
+      hop = switch (_mode!) {
+        _TrainHoppingMode.minimize => _nextTrain!.value <= _currentTrain!.value,
+        _TrainHoppingMode.maximize => _nextTrain!.value >= _currentTrain!.value,
+      };
       if (hop) {
         _currentTrain!
           ..removeStatusListener(_statusChangeHandler)

packages/flutter/lib/src/cupertino/date_picker.dart

@@ -414,20 +414,18 @@ class CupertinoDatePicker extends StatefulWidget {
   final double itemExtent;
 
   @override
-  State<StatefulWidget> createState() { // ignore: no_logic_in_create_state, https://github.com/flutter/flutter/issues/70499
-    // The `time` mode and `dateAndTime` mode of the picker share the time
-    // columns, so they are placed together to one state.
-    // The `date` mode has different children and is implemented in a different
-    // state.
-    switch (mode) {
-      case CupertinoDatePickerMode.time:
-      case CupertinoDatePickerMode.dateAndTime:
-        return _CupertinoDatePickerDateTimeState();
-      case CupertinoDatePickerMode.date:
-        return _CupertinoDatePickerDateState(dateOrder: dateOrder);
-      case CupertinoDatePickerMode.monthYear:
-        return _CupertinoDatePickerMonthYearState(dateOrder: dateOrder);
-    }
+  State<StatefulWidget> createState() {
+    // ignore: no_logic_in_create_state, https://github.com/flutter/flutter/issues/70499
+    return switch (mode) {
+      // The `time` mode and `dateAndTime` mode of the picker share the time
+      // columns, so they are placed together to one state.
+      // The `date` mode has different children and is implemented in a different
+      // state.
+      CupertinoDatePickerMode.time        => _CupertinoDatePickerDateTimeState(),
+      CupertinoDatePickerMode.dateAndTime => _CupertinoDatePickerDateTimeState(),
+      CupertinoDatePickerMode.date        => _CupertinoDatePickerDateState(dateOrder: dateOrder),
+      CupertinoDatePickerMode.monthYear   => _CupertinoDatePickerMonthYearState(dateOrder: dateOrder),
+    };
   }
 
   // Estimate the minimum width that each column needs to layout its content.

packages/flutter/lib/src/cupertino/list_tile.dart

@@ -287,15 +287,12 @@ class _CupertinoListTileState extends State<CupertinoListTile> {
       child: widget.title,
     );
 
-    EdgeInsetsGeometry? padding = widget.padding;
-    if (padding == null) {
-      switch (widget._type) {
-        case _CupertinoListTileType.base:
-          padding = widget.subtitle == null ? _kPadding : _kPaddingWithSubtitle;
-        case _CupertinoListTileType.notched:
-          padding = widget.leading == null ? _kNotchedPaddingWithoutLeading : _kNotchedPadding;
-      }
-    }
+    final EdgeInsetsGeometry padding = widget.padding ?? switch (widget._type) {
+      _CupertinoListTileType.base when widget.subtitle != null => _kPaddingWithSubtitle,
+      _CupertinoListTileType.notched when widget.leading != null => _kNotchedPadding,
+      _CupertinoListTileType.base => _kPadding,
+      _CupertinoListTileType.notched => _kNotchedPaddingWithoutLeading,
+    };
 
     Widget? subtitle;
     if (widget.subtitle != null) {
@@ -325,13 +322,12 @@ class _CupertinoListTileState extends State<CupertinoListTile> {
       backgroundColor = widget.backgroundColorActivated ?? CupertinoColors.systemGrey4.resolveFrom(context);
     }
 
-    double minHeight;
-    switch (widget._type) {
-      case _CupertinoListTileType.base:
-        minHeight = subtitle == null ? _kMinHeight : _kMinHeightWithSubtitle;
-      case _CupertinoListTileType.notched:
-        minHeight = widget.leading == null ? _kNotchedMinHeightWithoutLeading : _kNotchedMinHeight;
-    }
+    final double minHeight = switch (widget._type) {
+      _CupertinoListTileType.base when subtitle != null => _kMinHeightWithSubtitle,
+      _CupertinoListTileType.notched when widget.leading != null => _kNotchedMinHeight,
+      _CupertinoListTileType.base => _kMinHeight,
+      _CupertinoListTileType.notched => _kNotchedMinHeightWithoutLeading,
+    };
 
     final Widget child = Container(
       constraints: BoxConstraints(minWidth: double.infinity, minHeight: minHeight),

packages/flutter/lib/src/cupertino/route.dart

@@ -975,16 +975,10 @@ class _CupertinoEdgeShadowPainter extends BoxPainter {
 
     final TextDirection? textDirection = configuration.textDirection;
     assert(textDirection != null);
-    final double start;
-    final double shadowDirection; // -1 for ltr, 1 for rtl.
-    switch (textDirection!) {
-      case TextDirection.rtl:
-        start = offset.dx + configuration.size!.width;
-        shadowDirection = 1;
-      case TextDirection.ltr:
-        start = offset.dx;
-        shadowDirection = -1;
-    }
+    final (double shadowDirection, double start) = switch (textDirection!) {
+      TextDirection.rtl => (1, offset.dx + configuration.size!.width),
+      TextDirection.ltr => (-1, offset.dx),
+    };
 
     int bandColorIndex = 0;
     for (int dx = 0; dx < shadowWidth; dx += 1) {

packages/flutter/lib/src/cupertino/scrollbar.dart

@@ -174,12 +174,10 @@ class _CupertinoScrollbarState extends RawScrollbarState<CupertinoScrollbar> {
     if (direction == null) {
       return;
     }
-    switch (direction) {
-      case Axis.vertical:
-        _pressStartAxisPosition = localPosition.dy;
-      case Axis.horizontal:
-        _pressStartAxisPosition = localPosition.dx;
-    }
+    _pressStartAxisPosition = switch (direction) {
+      Axis.vertical   => localPosition.dy,
+      Axis.horizontal => localPosition.dx,
+    };
   }
 
   @override

packages/flutter/lib/src/cupertino/slider.dart

@@ -503,19 +503,10 @@ class _RenderCupertinoSlider extends RenderConstrainedBox implements MouseTracke
 
   @override
   void paint(PaintingContext context, Offset offset) {
-    final double visualPosition;
-    final Color leftColor;
-    final Color rightColor;
-    switch (textDirection) {
-      case TextDirection.rtl:
-        visualPosition = 1.0 - _position.value;
-        leftColor = _activeColor;
-        rightColor = trackColor;
-      case TextDirection.ltr:
-        visualPosition = _position.value;
-        leftColor = trackColor;
-        rightColor = _activeColor;
-    }
+    final (double visualPosition, Color leftColor, Color rightColor) = switch (textDirection) {
+      TextDirection.rtl => (1.0 - _position.value, _activeColor, trackColor),
+      TextDirection.ltr => (_position.value, trackColor, _activeColor),
+    };
 
     final double trackCenter = offset.dy + size.height / 2.0;
     final double trackLeft = offset.dx + _trackLeft;

packages/flutter/lib/src/material/button_bar.dart

@@ -429,12 +429,10 @@ class _RenderButtonBarRow extends RenderFlex {
             }
         }
         currentHeight += child.size.height;
-        switch (verticalDirection) {
-          case VerticalDirection.down:
-            child = childParentData.nextSibling;
-          case VerticalDirection.up:
-            child = childParentData.previousSibling;
-        }
+        child = switch (verticalDirection) {
+          VerticalDirection.down => childParentData.nextSibling,
+          VerticalDirection.up   => childParentData.previousSibling,
+        };
 
         if (overflowButtonSpacing != null && child != null) {
           currentHeight += overflowButtonSpacing!;

packages/flutter/lib/src/material/button_theme.dart

@@ -617,21 +617,11 @@ class ButtonThemeData with Diagnosticable {
   /// [getTextTheme] is [ButtonTextTheme.primary], 16.0 on the left and right
   /// otherwise.
   EdgeInsetsGeometry getPadding(MaterialButton button) {
-    if (button.padding != null) {
-      return button.padding!;
-    }
-
-    if (_padding != null) {
-      return _padding;
-    }
-
-    switch (getTextTheme(button)) {
-      case ButtonTextTheme.normal:
-      case ButtonTextTheme.accent:
-        return const EdgeInsets.symmetric(horizontal: 16.0);
-      case ButtonTextTheme.primary:
-        return const EdgeInsets.symmetric(horizontal: 24.0);
-    }
+    return button.padding ?? _padding ?? switch (getTextTheme(button)) {
+      ButtonTextTheme.normal  => const EdgeInsets.symmetric(horizontal: 16.0),
+      ButtonTextTheme.accent  => const EdgeInsets.symmetric(horizontal: 16.0),
+      ButtonTextTheme.primary => const EdgeInsets.symmetric(horizontal: 24.0),
+    };
   }
 
   /// The shape of the [button]'s [Material].

packages/flutter/lib/src/material/card.dart

@@ -213,14 +213,11 @@ class Card extends StatelessWidget {
     final CardTheme cardTheme = CardTheme.of(context);
     final CardTheme defaults;
     if (Theme.of(context).useMaterial3) {
-      switch (_variant) {
-        case _CardVariant.elevated:
-          defaults = _CardDefaultsM3(context);
-        case _CardVariant.filled:
-          defaults = _FilledCardDefaultsM3(context);
-        case _CardVariant.outlined:
-          defaults = _OutlinedCardDefaultsM3(context);
-      }
+      defaults = switch (_variant) {
+        _CardVariant.elevated => _CardDefaultsM3(context),
+        _CardVariant.filled   => _FilledCardDefaultsM3(context),
+        _CardVariant.outlined => _OutlinedCardDefaultsM3(context),
+      };
     } else {
       defaults = _CardDefaultsM2(context);
     }