hash_and_equals

Missing a corresponding override of '{0}'.

The analyzer produces this diagnostic when a class or mixin either overrides the definition of == but doesn't override the definition of hashCode, or conversely overrides the definition of hashCode but doesn't override the definition of ==.

Both the == operator and the hashCode property of objects must be consistent for a common hash map implementation to function properly. As a result, when overriding either method, both should be overridden.

The following code produces this diagnostic because the class C overrides the == operator but doesn't override the getter hashCode:

class C {
  final int value;
​
  C(this.value);
​
  @override
  bool operator ==(Object other) =>
      other is C &&
      other.runtimeType == runtimeType &&
      other.value == value;
}

If you need to override one of the members, then add an override of the other:

class C {
  final int value;
​
  C(this.value);
​
  @override
  bool operator ==(Object other) =>
      other is C &&
      other.runtimeType == runtimeType &&
      other.value == value;
​
  @override
  int get hashCode => value.hashCode;
}

If you don't need to override either of the members, then remove the unnecessary override:

class C {
  final int value;
​
  C(this.value);
}