avoid_constant_switches

v0.4.0 Warning Control Flow

Warns when a switch statement or switch expression evaluates a constant expression. Since the value never changes, the switch always takes the same branch, making all other cases dead code. This usually indicates a typo or a bug.

Why use this rule

Switching on a constant means only one branch can ever execute, turning the switch into expensive dead code. This is typically a mistake — the developer likely intended to switch on a variable or parameter instead of a compile-time constant. Catching this early prevents unreachable code from accumulating.

See also: Effective Dart: Usage

Don’t

const _another = 10;

abstract final class Config {
  static const value = '1';
}

void bad() {
  // Switching on a static const field
  switch (Config.value) {
    case '1':
      print('always');
    case '2':
      print('never');
  }

  // Switching on a top-level const
  switch (_another) {
    case 10:
      print('always');
    default:
      print('never');
  }

  // Switch expression on an integer literal
  final x = switch (42) {
    42 => 'yes',
    _ => 'no',
  };
}

Do

void good(int another) {
  // Parameter
  switch (another) {
    case 10:
      print('maybe');
    default:
      print('maybe');
  }

  // Switch expression on parameter
  final x = switch (another) {
    10 => 'ten',
    _ => 'other',
  };

  // Method call result
  switch (another.toString()) {
    case '10':
      print('maybe');
  }
}

Configuration

To disable this rule:

plugins:
  many_lints:
    diagnostics:
      avoid_constant_switches: false