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prefer-contains

Same as prefer_contains in Dart lints

Group: Performance
Path: lint/performance/prefer-contains
Default: On (recommended)
Origin: Dart lints
Rule: 334 of 512

recommended

Prefers contains to comparing the result of indexOf with a constant.

The rule looks at a comparison (==, !=, <, <=, >, >=) of an Iterable or String receiver's indexOf(...) call (optionally behind as casts) with an integer constant <= 0 on the other side: an integer literal, a negated literal or identifier, or an identifier naming an int constant. When the call has exactly two arguments the second (the start index) must be the constant 0. Comparisons with -1 (==, !=, <= and > after normalizing the call to the left) and 0 (>=, <) are membership tests that contains states directly; comparisons that are always true or false (< -1, >= -1, or any comparison with a value below -1) are reported too. A constant on the right is preferred: when the right operand is an integer constant the left operand is not considered.

Invalid

example.dartdart

bool missing(List<String> values, String value) {
  return values.indexOf(value) == -1;
}
bool present(String text, String value) {
  return text.indexOf(value) >= 0;
}
bool defaultValue([bool found = 'abc'.indexOf('a') >= 0]) => found;
bool swappedPresent(List<String> values, String value) {
  return -1 < values.indexOf(value);
}
bool swappedMissing(String text, String value) {
  return 0 <= text.indexOf(value);
}
bool otherForms(String text, String value) {
  if (text.indexOf(value) < 0) return false;
  if (text.indexOf(value) <= -1) return false;
  if (-1 >= text.indexOf(value)) return false;
  return text.indexOf(value) != -1;
}
bool hexBounds(String text, String value) {
  if (text.indexOf(value) != -0x1) return true;
  return text.indexOf(value) >= 0x0;
}

class SearchState {
  final bool found;
  SearchState(String text) : found = text.indexOf('x') >= 0;

  bool get fromGetter {
    String text = 'abc';
    return text.indexOf('a') >= 0;
  }

  set values(List<String> values) {
    values.indexOf('x') >= 0;
  }

  bool operator ==(Object other) {
    String text = other.toString();
    return text.indexOf('x') >= 0;
  }
}

void scoped(List<String> values, List<String> texts) {
  bool local(String text) => text.indexOf('x') >= 0;
  for (String text in texts) {
    text.indexOf('x') >= 0;
  }
  try {
    throw 'x';
  } on String catch (text) {
    text.indexOf('x') >= 0;
  }
  final (String text,) = ('abc',);
  text.indexOf('x') >= 0;
}

const minusOne = -1;
const zero = 0;

bool startArguments(String text, String value) {
  if (text.indexOf(value, 0) >= 0) return true;
  if (text.indexOf(value, zero) >= 0) return true;
  return text.indexOf('x', 1, 2) >= 0;
}

bool constants(List<int> values, String text, List<int>? maybe, Object other) {
  if (values.indexOf(1) == minusOne) return true;
  if (text.indexOf('x') >= zero) return true;
  if (maybe?.indexOf(1) == -1) return true;
  if ((other as List<int>).indexOf(1) == -1) return true;
  return 0 > values.indexOf(1);
}

bool alwaysTrueOrFalse(String text) {
  if (text.indexOf('x') < -1) return true;
  if (text.indexOf('x') >= -1) return true;
  if (text.indexOf('x') == -2) return true;
  return text.indexOf('x') != -2;
}

Use `contains` instead of comparing the result of `indexOf`.

1bool missing(List<String> values, String value) {

2 return values.indexOf(value) == -1;

∙

Use `contains` instead of comparing the result of `indexOf`.

4bool present(String text, String value) {

5 return text.indexOf(value) >= 0;

∙

Use `contains` instead of comparing the result of `indexOf`.

6}

7bool defaultValue([bool found = 'abc'.indexOf('a') >= 0]) => found;

∙

Use `contains` instead of comparing the result of `indexOf`.

8bool swappedPresent(List<String> values, String value) {

9 return -1 < values.indexOf(value);

∙

Use `contains` instead of comparing the result of `indexOf`.

11bool swappedMissing(String text, String value) {

12 return 0 <= text.indexOf(value);

∙

Use `contains` instead of comparing the result of `indexOf`.

14bool otherForms(String text, String value) {

15 if (text.indexOf(value) < 0) return false;

∙

Use `contains` instead of comparing the result of `indexOf`.

15 if (text.indexOf(value) < 0) return false;

16 if (text.indexOf(value) <= -1) return false;

∙

Use `contains` instead of comparing the result of `indexOf`.

16 if (text.indexOf(value) <= -1) return false;

17 if (-1 >= text.indexOf(value)) return false;

∙

Use `contains` instead of comparing the result of `indexOf`.

17 if (-1 >= text.indexOf(value)) return false;

18 return text.indexOf(value) != -1;

∙

Use `contains` instead of comparing the result of `indexOf`.

20bool hexBounds(String text, String value) {

21 if (text.indexOf(value) != -0x1) return true;

∙

Use `contains` instead of comparing the result of `indexOf`.

21 if (text.indexOf(value) != -0x1) return true;

22 return text.indexOf(value) >= 0x0;

∙

Use `contains` instead of comparing the result of `indexOf`.

26 final bool found;

27 SearchState(String text) : found = text.indexOf('x') >= 0;

∙

Use `contains` instead of comparing the result of `indexOf`.

30 String text = 'abc';

31 return text.indexOf('a') >= 0;

∙

Use `contains` instead of comparing the result of `indexOf`.

34 set values(List<String> values) {

35 values.indexOf('x') >= 0;

∙

Use `contains` instead of comparing the result of `indexOf`.

39 String text = other.toString();

40 return text.indexOf('x') >= 0;

∙

Use `contains` instead of comparing the result of `indexOf`.

44void scoped(List<String> values, List<String> texts) {

45 bool local(String text) => text.indexOf('x') >= 0;

∙

Use `contains` instead of comparing the result of `indexOf`.

46 for (String text in texts) {

47 text.indexOf('x') >= 0;

∙

Use `contains` instead of comparing the result of `indexOf`.

51 } on String catch (text) {

52 text.indexOf('x') >= 0;

∙

Use `contains` instead of comparing the result of `indexOf`.

54 final (String text,) = ('abc',);

55 text.indexOf('x') >= 0;

∙

Use `contains` instead of comparing the result of `indexOf`.

61bool startArguments(String text, String value) {

62 if (text.indexOf(value, 0) >= 0) return true;

∙

Use `contains` instead of comparing the result of `indexOf`.

62 if (text.indexOf(value, 0) >= 0) return true;

63 if (text.indexOf(value, zero) >= 0) return true;

∙

Use `contains` instead of comparing the result of `indexOf`.

63 if (text.indexOf(value, zero) >= 0) return true;

64 return text.indexOf('x', 1, 2) >= 0;

∙

Use `contains` instead of comparing the result of `indexOf`.

67bool constants(List<int> values, String text, List<int>? maybe, Object other) {

68 if (values.indexOf(1) == minusOne) return true;

∙

Use `contains` instead of comparing the result of `indexOf`.

68 if (values.indexOf(1) == minusOne) return true;

69 if (text.indexOf('x') >= zero) return true;

∙

Use `contains` instead of comparing the result of `indexOf`.

69 if (text.indexOf('x') >= zero) return true;

70 if (maybe?.indexOf(1) == -1) return true;

∙

Use `contains` instead of comparing the result of `indexOf`.

70 if (maybe?.indexOf(1) == -1) return true;

71 if ((other as List<int>).indexOf(1) == -1) return true;

∙

Use `contains` instead of comparing the result of `indexOf`.

71 if ((other as List<int>).indexOf(1) == -1) return true;

72 return 0 > values.indexOf(1);

∙

This comparison of `indexOf` is always false.

75bool alwaysTrueOrFalse(String text) {

76 if (text.indexOf('x') < -1) return true;

∙

This comparison of `indexOf` is always true.

76 if (text.indexOf('x') < -1) return true;

77 if (text.indexOf('x') >= -1) return true;

∙

This comparison of `indexOf` is always false.

77 if (text.indexOf('x') >= -1) return true;

78 if (text.indexOf('x') == -2) return true;

∙

This comparison of `indexOf` is always true.

78 if (text.indexOf('x') == -2) return true;

79 return text.indexOf('x') != -2;

∙

Valid

example.dartdart

bool present(List<String> values, String value) => values.contains(value);
class Search { int indexOf(Object value) => 0; }
bool custom(Search value) => value.indexOf('x') == -1;
bool listStart(List<String> values, String value) => values.indexOf(value, 1) >= 0;
bool stringNonzeroStart(String text, String value) => text.indexOf(value, 2) >= 0;

const minusOneDouble = -1.0;
bool doubleConstant(String text) => text.indexOf('x') == minusOneDouble;
bool assigned(String text) {
  int index;
  return (index = text.indexOf('x')) != -1;
}
bool positive(String text) => text.indexOf('x') > 0;

class List<E> {
  int indexOf(E value) => 0;
}
bool ambiguousList(List<String> values, String value) => values.indexOf(value) >= 0;

Configure prefer-contains

Set its severity in falcon.json. See the configuration guide.

falcon.jsonjson

{
  "linter": {
    "rules": {
      "performance": {
        "prefer-contains": "error"
      }
    }
  }
}

Or silence one occurrence with a suppression comment; the reason is required.

example.dartdart

// falcon-ignore lint/performance/prefer-contains: <reason>

prefer-correct-edge-insets-constructorprefer-correct-edge-insets-constructorrecommendedflutter
Flags an EdgeInsets.only(...) that a more specific constructor expresses better.
prefer-declaring-const-constructorprefer_declaring_const_constructorflutter
Flags a generative constructor that is legally eligible to be const.
prefer-foreachprefer_foreach
Prefers forEach to a for-in loop that only passes each element to a function.
prefer-return-await
Await returned SDK Futures inside a try body protected by a catch clause.
prefer-single-setstateflutter
Merge consecutive Flutter State.setState statements in the same block.
prefer-use-callbackflutter_hooks
Prefer useCallback for synchronous memoized function literals.
prefer-use-memoflutter_hooks
Prefer memoizing freshly allocated collection values used as hook keys.
prefer-using-list-viewflutter
Suggests considering ListView for a SingleChildScrollView containing a plain Flutter Column with at least two unconditional children in a list literal.