prefer_conditional_expressions

v1.0.0WarningControl Flow

This rule flags an if/else that does nothing but assign or return two values.

Six lines to choose between two strings buries the one thing that varies. A conditional expression puts the choice and both outcomes on one line, and makes it obvious that every path assigns exactly once — which the block form only implies.

Don’t

Both branches assign the same target:

String describe({required bool isActive}) {
  String label;
  if (isActive) {
    label = 'On';
  } else {
    label = 'Off';
  }
  return label;
}

Both branches return:

String greeting({required bool isMorning}) {
  if (isMorning) {
    return 'Good morning';
  } else {
    return 'Good evening';
  }
}

Do

String describe({required bool isActive}) {
  final label = isActive ? 'On' : 'Off';
  return label;
}

String greeting({required bool isMorning}) =>
    isMorning ? 'Good morning' : 'Good evening';

Known limitations

Only the two shapes where the rewrite is exact are reported. These are all left alone, because collapsing them would change what the code does:

String describe({required bool isActive}) {
  String label;
  String tone;

  // Two statements in a branch.
  if (isActive) {
    label = 'On';
    tone = 'green';
  } else {
    label = 'Off';
    tone = 'grey';
  }

  // Different targets.
  if (isActive) {
    label = 'On';
  } else {
    tone = 'grey';
  }

  // Different operators — `=` in one branch, `+=` in the other.
  if (isActive) {
    label = 'On';
  } else {
    label += 'Off';
  }

  // No `else`.
  if (isActive) {
    label = 'On';
  }

  return '$label$tone';
}

An else if chain is a sequence of tests rather than a two-way choice, and a pattern if (if (x case ...)) binds variables a conditional expression cannot — both are skipped.

Configuration

This rule is in the pedantic preset. Enable it by name:

many_lints.yaml

rules:
  prefer_conditional_expressions: true

To turn it off again:

many_lints.yaml

rules:
  prefer_conditional_expressions: false

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

Related rules

• avoid_nested_conditional_expressions — Flag a conditional nested inside another.
• prefer_switch_expression — Suggest converting switch statements to switch expressions.
• prefer_switch_with_enums — Use a switch instead of an if-else chain over enum constants.
• avoid_contradictory_expressions — Detect logical AND conditions that always evaluate to false.