falcon

Rules / Complexity / avoid-inverted-boolean-expressions

avoid-inverted-boolean-expressions

lint/complexity/avoid-inverted-boolean-expressions
recommended
Same as avoid_inverted_boolean_expressions · Pyramid Lint

Flags a doubly-negated boolean expression such as !!x.

Two ! operators cancel out, so !!x is just x, and a longer run of leading bangs reduces to x or !x by parity. The redundant negation adds no meaning and obscures the value. The rule flags a ! whose operand is itself a !, reporting once at the outer negation and skipping the inner bangs. Despite the rule's name, it targets only stacked negations — it does not rewrite !(a == b) into a != b.

Invalid

example.dartdart
class BooleanExpressions {
  void examples() {
    bool isValid = true;
    bool condition = false;

    /// Double negation with double bang
    if (!!isValid) {
      print('valid');
    }

    /// Nested negation
    if (!(!condition)) {
      print('condition met');
    }

    /// Double negation in assignment
    final result = !!isValid;
    print(result);

    /// Double negation in variable declaration
    var flag = !!condition;

    /// Negation of negation in return
    if (!(!isValid)) {
      return;
    }

    /// Triple negation (still bad)
    bool x = !!!isValid;
  }
}
Avoid inverted boolean expressions. Simplify the double negation.
6 /// Double negation with double bang
7 if (!!isValid) {
Avoid inverted boolean expressions. Simplify the double negation.
11 /// Nested negation
12 if (!(!condition)) {
Avoid inverted boolean expressions. Simplify the double negation.
16 /// Double negation in assignment
17 final result = !!isValid;
Avoid inverted boolean expressions. Simplify the double negation.
20 /// Double negation in variable declaration
21 var flag = !!condition;
Avoid inverted boolean expressions. Simplify the double negation.
23 /// Negation of negation in return
24 if (!(!isValid)) {
Avoid inverted boolean expressions. Simplify the double negation.
28 /// Triple negation (still bad)
29 bool x = !!!isValid;

Valid

example.dartdart
class BooleanExpressions {
  void examples() {
    bool isValid = true;
    bool condition = false;

    /// Direct boolean check
    if (isValid) {
      print('valid');
    }

    /// Single negation
    if (!condition) {
      print('condition met');
    }

    /// Direct assignment
    final result = isValid;
    print(result);

    /// Single negation in assignment
    var flag = !condition;

    /// Single negation in return
    if (isValid) {
      return;
    }

    /// Simple negation
    bool x = !isValid;
  }
}

How to configure

Set the severity of avoid-inverted-boolean-expressions in your falcon.json:

falcon.jsonjson
{
  "linter": {
    "rules": {
      "complexity": {
        "avoid-inverted-boolean-expressions": "error"
      }
    }
  }
}

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