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iterable_contains_unrelated_type

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Removed

Invocation of Iterable<E>.contains with references of unrelated types.

Details

#

NOTE: This rule is removed in Dart 3.3.0; it is no longer functional.

DON'T invoke contains on Iterable with an instance of different type than the parameter type.

Doing this will invoke == on its elements and most likely will return false.

BAD:

dart
void someFunction() {
  var list = <int>[];
  if (list.contains('1')) print('someFunction'); // LINT
}

BAD:

dart
void someFunction3() {
  List<int> list = <int>[];
  if (list.contains('1')) print('someFunction3'); // LINT
}

BAD:

dart
void someFunction8() {
  List<DerivedClass2> list = <DerivedClass2>[];
  DerivedClass3 instance;
  if (list.contains(instance)) print('someFunction8'); // LINT
}

BAD:

dart
abstract class SomeIterable<E> implements Iterable<E> {}

abstract class MyClass implements SomeIterable<int> {
  bool badMethod(String thing) => this.contains(thing); // LINT
}

GOOD:

dart
void someFunction10() {
  var list = [];
  if (list.contains(1)) print('someFunction10'); // OK
}

GOOD:

dart
void someFunction1() {
  var list = <int>[];
  if (list.contains(1)) print('someFunction1'); // OK
}

GOOD:

dart
void someFunction4() {
  List<int> list = <int>[];
  if (list.contains(1)) print('someFunction4'); // OK
}

GOOD:

dart
void someFunction5() {
  List<ClassBase> list = <ClassBase>[];
  DerivedClass1 instance;
  if (list.contains(instance)) print('someFunction5'); // OK
}

abstract class ClassBase {}

class DerivedClass1 extends ClassBase {}

GOOD:

dart
void someFunction6() {
  List<Mixin> list = <Mixin>[];
  DerivedClass2 instance;
  if (list.contains(instance)) print('someFunction6'); // OK
}

abstract class ClassBase {}

abstract class Mixin {}

class DerivedClass2 extends ClassBase with Mixin {}

GOOD:

dart
void someFunction7() {
  List<Mixin> list = <Mixin>[];
  DerivedClass3 instance;
  if (list.contains(instance)) print('someFunction7'); // OK
}

abstract class ClassBase {}

abstract class Mixin {}

class DerivedClass3 extends ClassBase implements Mixin {}

Enable

#

To enable the iterable_contains_unrelated_type rule, add iterable_contains_unrelated_type under linter > rules in your analysis_options.yaml file:

analysis_options.yaml
yaml
linter:
  rules:
    - iterable_contains_unrelated_type

If you're instead using the YAML map syntax to configure linter rules, add iterable_contains_unrelated_type: true under linter > rules:

analysis_options.yaml
yaml
linter:
  rules:
    iterable_contains_unrelated_type: true

Unless stated otherwise, the documentation on this site reflects Dart 3.7.3. Page last updated on 2025-03-07. View source or report an issue.