avoid-bottom-type-in-patterns

v1.5.0

dart 3.0+

pro+

Warns when a pattern contains a void, Never or Null type.

Presence of these types inside a pattern is most likely a bug.

Example

❌ Bad:

final object = WithField('hello');

// LINT: Avoid the 'Null' type inside patterns. Try using a different type.
if (object case Null()) {}
// LINT: Avoid the 'Never' type inside patterns. Try using a different type.
if (object case Never()) {}

// LINT: Avoid the 'Null' type inside patterns. Try using a different type.
if (object case final Null value) {}
// LINT: Avoid the 'Never' type inside patterns. Try using a different type.
if (object case final Never value) {}

final value = switch (object) {
  // LINT: Avoid the 'Null' type inside patterns. Try using a different type.
  Null() => 'bad',
  // LINT: Avoid the 'Never' type inside patterns. Try using a different type.
  Never() => 'bad',
};

✅ Good:

final object = WithField('hello');

if (object == null) {}
if (object case == null) {} // Correct, 'null' instead of 'Null'

if (object case WithField()) {}

final value = switch (object) {
  == null => 'good',
  _ => 'good',
};

Additional Resources

Top and bottom types in Dart