avoid-non-exhaustive-switch-on-sealed-classes

added in: 4.2.0 style

Warns when a switch over a sealed type uses a default case or an unguarded wildcard (_) case.

A fallback case handles every otherwise-unmatched value, so the compiler cannot identify newly added subtypes that are not handled explicitly. Listing every subtype preserves exhaustiveness checking and makes each decision visible.

Example

Bad:

sealed class Shape {}

final class Circle extends Shape {}
final class Square extends Shape {}

String describe(Shape shape) => switch (shape) {
  Circle() => 'circle',
  _ => 'unknown', // LINT
};

Good:

String describe(Shape shape) => switch (shape) {
  Circle() => 'circle',
  Square() => 'square',
};

The rule applies to switch statements and switch expressions. Guarded wildcards such as case _ when condition are allowed because they do not satisfy exhaustiveness by themselves, so the compiler still requires the remaining subtypes to be handled.

Additional resources:

• Dart exhaustiveness checking
• Dart sealed types