prefer_wildcard_pattern

v0.4.0 Warning Fix Pattern Matching

This rule flags a bare Object() pattern used as a catch-all. It matches everything non-null, exactly like _, but reads as if it were testing for something. The quick fix replaces it with _.

It applies in switch expressions, switch statements, and if-case conditions.

See also: Dart patterns

Don’t

String describe(Object value) {
  return switch (value) {
    int() => 'a number',
    String() => 'text',
    Object() => 'something else',    // LINT
  };
}

void log(Object value) {
  switch (value) {
    case int():
      print('int');
    case Object():                   // LINT
      print('other');
  }
}

void guard(Object value) {
  if (value case Object()) {         // LINT
    print('always runs');
  }
}

Do

String describe(Object value) {
  return switch (value) {
    int() => 'a number',
    String() => 'text',
    _ => 'something else',
  };
}

void log(Object value) {
  switch (value) {
    case int():
      print('int');
    case _:
      print('other');
  }
}

void guard(Object value) {
  print('always runs');
}

That last one is the case worth noticing: if (x case Object()) is a condition that is always true for a non-null value, so the if itself was doing nothing.

Known limitations

Object() with fields is left alone. Once the pattern destructures something it is doing real work, and _ cannot replace it:

// Not reported — the pattern extracts a value
String describe(Object value) => switch (value) {
  Object(hashCode: final h) => 'hash: $h',
};

Named types other than Object are not the target. int(), String(), or your own Response() narrow the match and are never reported.

Nested inside && and || still counts. Object() && Object() reports both operands, since each one is independently a catch-all.

The type name is matched textually. A class of your own named Object in scope would be reported as well.

Configuration

This rule is in the recommended preset, so it is on with preset: recommended or preset: opinionated. Add it to preset: core with prefer_wildcard_pattern: true.

To turn it off:

many_lints.yaml

rules:
  prefer_wildcard_pattern: false

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

Related rules

• avoid_wildcard_cases_with_enums — Opposing convention. Keep exhaustiveness checking by listing enum cases explicitly.
• prefer_switch_with_enums — Use a switch instead of an if-else chain over enum constants.
• avoid_single_field_destructuring — Avoid destructuring a single field when direct property access is simpler.
• use_existing_destructuring — Add properties to an existing destructuring instead of accessing them directly.