prefer_switch_expression

v0.3.0WarningFixConfigurableControl Flow

Warns when a switch statement can be converted to a switch expression. This applies when all branches either return a value or assign to the same variable, with each case containing exactly one statement.

Why use this rule

Dart 3 introduced switch expressions as a more concise alternative to switch statements for simple value-producing switches. They reduce boilerplate (case, return, break), make it clear that the switch produces a value, and are easier to read when each branch is a single expression. The quick fix handles the conversion automatically.

See also: Switch expressions

Don’t

// All cases return a value — use switch expression
DeliveryIcon iconForBad(DeliveryStage stage) {
  switch (stage) {
    case DeliveryStage.packed:
      return DeliveryIcon.box;
    case DeliveryStage.shipped:
      return DeliveryIcon.truck;
    case DeliveryStage.delivered:
      return DeliveryIcon.home;
  }
}

// All cases assign to the same variable
String getDescriptionBad(DeliveryIcon icon) {
  String description;
  switch (icon) {
    case DeliveryIcon.box:
      description = 'Waiting in the warehouse';
    case DeliveryIcon.truck:
      description = 'On the road';
    case DeliveryIcon.home:
      description = 'Dropped at the door';
  }
  return description;
}

Do

// Switch expression with return
DeliveryIcon iconForGood(DeliveryStage stage) {
  return switch (stage) {
    DeliveryStage.packed => DeliveryIcon.box,
    DeliveryStage.shipped => DeliveryIcon.truck,
    DeliveryStage.delivered => DeliveryIcon.home,
  };
}

// Switch expression with assignment
String getDescriptionGood(DeliveryIcon icon) {
  final description = switch (icon) {
    DeliveryIcon.box => 'Waiting in the warehouse',
    DeliveryIcon.truck => 'On the road',
    DeliveryIcon.home => 'Dropped at the door',
  };
  return description;
}

// Switch expression with default case (using wildcard)
String getNameGood(int value) {
  return switch (value) {
    1 => 'one',
    2 => 'two',
    _ => 'unknown',
  };
}

Turning this rule off

This rule is in the opinionated preset, so it is on with preset: opinionated, or by name:

many_lints.yaml

rules:
  prefer_switch_expression: true

To turn it off again:

many_lints.yaml

rules:
  prefer_switch_expression: false

To keep the rule on but skip certain paths, use per-rule exclude.

Options

analysis_options.yaml

analysis_options.yaml

many_lints:
  rules:
    prefer_switch_expression:
      allow_fallthrough_cases: true

many_lints.yaml

many_lints.yaml

rules:
  prefer_switch_expression:
    allow_fallthrough_cases: true

Option	Type	Default	Description
allow_fallthrough_cases	bool	false	Also report switches where labels share a body. The quick fix merges them into a single `case a

Related rules

• avoid_nested_conditional_expressions — Flag a conditional nested inside another.
• prefer_conditional_expressions — Collapse a two-way if/else into a conditional expression.
• prefer_switch_with_enums — Use a switch instead of an if-else chain over enum constants.
• no_equal_switch_case — Flag two switch branches with identical bodies.