falcon

Rules / Correctness / hash-and-equals

hash-and-equals

lint/correctness/hash-and-equals
recommended
Same as hash_and_equals · Dart lints

Require hashCode and == to be overridden together.

Flags a class, mixin, or mixin class that overrides the == operator without also defining hashCode, or defines hashCode without overriding ==. The two are bound by a contract: any two objects that compare equal must return the same hash code. Overriding only one breaks that invariant, so the type misbehaves as a Map key or Set element — lookups miss and duplicates slip through. Override both and derive them from the same fields.

Invalid

example.dartdart
class A {
  @override bool operator ==(Object other) => identical(this, other);
}

class B {
  @override int get hashCode => 42;
}

class C {
  @override final int hashCode = 7;
}

mixin M {
  @override bool operator ==(Object other) => true;
}

class D {
  final int value = 0;
  @override bool operator ==(Object other) => other is D;
}
Override 'hashCode' if you override the '==' operator.
1class A {
2 @override bool operator ==(Object other) => identical(this, other);
Override the '==' operator if you override 'hashCode'.
5class B {
6 @override int get hashCode => 42;
Override the '==' operator if you override 'hashCode'.
9class C {
10 @override final int hashCode = 7;
Override 'hashCode' if you override the '==' operator.
13mixin M {
14 @override bool operator ==(Object other) => true;
Override 'hashCode' if you override the '==' operator.
18 final int value = 0;
19 @override bool operator ==(Object other) => other is D;

Valid

example.dartdart
class A {
  @override
  bool operator ==(Object other) => identical(this, other);

  @override
  int get hashCode => 0;
}

class B {
  void method() {}
}

mixin M {
  @override
  bool operator ==(Object other) => true;

  @override
  int get hashCode => 1;
}

class C {
  final int value = 0;
  int get other => 0;
}

enum E { a, b }

How to configure

Set the severity of hash-and-equals in your falcon.json:

falcon.jsonjson
{
  "linter": {
    "rules": {
      "correctness": {
        "hash-and-equals": "error"
      }
    }
  }
}

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