refactor: Avoid nested conditional expressions whenever possible [DCM] (

#2784)

I was playing around with the rule avoid-nested-conditional-expressions.
While I philosophically agree with the rule, sadly Dart's new switch-as-an-expression, while a much-needed improvement, still pales in comparison to Kotlin's powerful when, which makes it impossible to convert all cases of nested ternaries into something actually better. In some cases, given the tools that Dart provides, I think nested ternary is the best option.
Notwithstanding, I used the rule to catch many cases where the new switch expression can be used to vastly simplify our codebase, making it much more readable.

packages/flame/lib/src/effects/controllers/zigzag_effect_controller.dart

@@ -24,10 +24,10 @@ class ZigzagEffectController extends DurationEffectController {
     // are 3 linear segments: at first it's y = x, for 0 ≤ x ≤ 1, then it's
     // y = -x + 2, for 1 ≤ x ≤ 3, and finally it's y = x + (-4), for 3 ≤ x ≤ 4.
     final x = timer / _quarterPeriod;
-    return x <= 1
-        ? x
-        : x >= 3
-            ? x - 4
-            : 2 - x;
+    return switch (x) {
+      <= 1 => x,
+      >= 3 => x - 4,
+      _ => 2 - x,
+    };
   }
 }

packages/flame/lib/src/game/game_widget/gesture_detector_builder.dart

@@ -179,10 +179,12 @@ bool hasMouseDetectors(Game game) {
 }
 
 Widget applyMouseDetectors(Game game, Widget child) {
-  final mouseMoveFn = game is MouseMovementDetector
-      ? game.onMouseMove
-      // ignore: deprecated_member_use_from_same_package
-      : (game is HasHoverables ? game.onMouseMove : null);
+  final mouseMoveFn = switch (game) {
+    MouseMovementDetector() => game.onMouseMove,
+    // ignore: deprecated_member_use_from_same_package
+    HasHoverables() => game.onMouseMove,
+    _ => null,
+  };
   final mouseDetector = game.mouseDetector;
   return Listener(
     child: MouseRegion(

packages/flame/test/effects/controllers/sequence_effect_controller_test.dart

@@ -54,11 +54,11 @@ void main() {
         expect(
           ec.progress,
           closeTo(
-            totalTime <= 1
-                ? totalTime
-                : totalTime <= 3
-                    ? (totalTime - 1) / 2
-                    : (totalTime - 3) / 3,
+            switch (totalTime) {
+              <= 1 => totalTime,
+              <= 3 => (totalTime - 1) / 2,
+              _ => (totalTime - 3) / 3,
+            },
             1e-15,
           ),
         );
@@ -84,11 +84,11 @@ void main() {
         expect(
           ec.progress,
           closeTo(
-            totalTime <= 1
-                ? totalTime
-                : totalTime <= 3
-                    ? (totalTime - 1) / 2
-                    : (totalTime - 3) / 3,
+            switch (totalTime) {
+              <= 1 => totalTime,
+              <= 3 => (totalTime - 1) / 2,
+              _ => (totalTime - 3) / 3,
+            },
             1e-14,
           ),
         );

packages/flame_jenny/jenny/lib/src/structure/expressions/expression.dart

@@ -3,18 +3,17 @@ abstract class Expression {
 
   dynamic get value;
 
-  bool get isNumeric => false;
-  bool get isBoolean => false;
-  bool get isString => false;
+  bool get isNumeric => type == ExpressionType.numeric;
+  bool get isBoolean => type == ExpressionType.boolean;
+  bool get isString => type == ExpressionType.string;
 
   ExpressionType get type {
-    return isNumeric
-        ? ExpressionType.numeric
-        : isBoolean
-            ? ExpressionType.boolean
-            : isString
-                ? ExpressionType.string
-                : ExpressionType.unknown;
+    return switch (this) {
+      NumExpression() => ExpressionType.numeric,
+      BoolExpression() => ExpressionType.boolean,
+      StringExpression() => ExpressionType.string,
+      _ => ExpressionType.unknown,
+    };
   }
 }
 
@@ -30,27 +29,18 @@ abstract class NumExpression extends Expression {
 
   @override
   num get value;
-
-  @override
-  bool get isNumeric => true;
 }
 
 abstract class StringExpression extends Expression {
   const StringExpression();
 
   @override
   String get value;
-
-  @override
-  bool get isString => true;
 }
 
 abstract class BoolExpression extends Expression {
   const BoolExpression();
 
   @override
   bool get value;
-
-  @override
-  bool get isBoolean => true;
 }

packages/flame_jenny/jenny/lib/src/variable_storage.dart

@@ -18,25 +18,25 @@ class VariableStorage {
 
   Expression getVariableAsExpression(String name) {
     final dynamic value = variables[name];
-    if (value is String) {
-      return StringVariable(name, this);
-    }
-    if (value is num) {
-      return NumericVariable(name, this);
-    }
-    assert(value is bool);
-    return BooleanVariable(name, this);
+    return switch (value) {
+      String() => StringVariable(name, this),
+      num() => NumericVariable(name, this),
+      bool() => BooleanVariable(name, this),
+      _ => throw DialogueError(
+          'Cannot convert variable $name with type ${value.runtimeType} to '
+          'an expression',
+        ),
+    };
   }
 
   ExpressionType getVariableType(String name) {
     final dynamic value = variables[name];
-    return value is String
-        ? ExpressionType.string
-        : value is num
-            ? ExpressionType.numeric
-            : value is bool
-                ? ExpressionType.boolean
-                : ExpressionType.unknown;
+    return switch (value) {
+      String() => ExpressionType.string,
+      num() => ExpressionType.numeric,
+      bool() => ExpressionType.boolean,
+      _ => ExpressionType.unknown,
+    };
   }
 
   void setVariable(String name, dynamic value) {