falcon

Rules / Style / prefer-is-not-operator

prefer-is-not-operator

lint/style/prefer-is-not-operator
recommended
Same as prefer_is_not_operator · Dart lints

Flags a negated type test !(x is T) that should use the is! operator.

Dart provides the is! operator precisely so negated type checks read directly as x is! T instead of wrapping the test in parentheses and negating it, which is easier to misread and to accidentally mis-parenthesize. The rule fires on a logical-not applied to a non-negated is expression; a test that already uses is! produces no negation to flag.

Invalid

example.dartdart
void f(Object x) {
  if (!(x is int)) {}
  var a = !(x is String);
  final b = !(x is List<int>);
  final c = !(x is double);
  print(!(x is bool));
  print('$a $b $c');
}
Prefer using the 'is!' operator.
1void f(Object x) {
2 if (!(x is int)) {}
Prefer using the 'is!' operator.
2 if (!(x is int)) {}
3 var a = !(x is String);
Prefer using the 'is!' operator.
3 var a = !(x is String);
4 final b = !(x is List<int>);
Prefer using the 'is!' operator.
4 final b = !(x is List<int>);
5 final c = !(x is double);
Prefer using the 'is!' operator.
5 final c = !(x is double);
6 print(!(x is bool));

Valid

example.dartdart
void f(Object x) {
  if (x is! int) {}
  var a = x is String;
  final b = !(x is! double);
  var c = !someBool(x);
  print(x is bool);
  print('$a $b $c');
}

bool someBool(Object x) => true;

How to configure

Set the severity of prefer-is-not-operator in your falcon.json:

falcon.jsonjson
{
  "linter": {
    "rules": {
      "style": {
        "prefer-is-not-operator": "error"
      }
    }
  }
}

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