prefer_equatable_mixin

v0.4.0 Warning Fix Type Annotations

Flags a class that extends Equatable from package:equatable instead of mixing in EquatableMixin. Both give the same value equality; only one leaves the extends slot free.

Don’t

Dart allows a single superclass. Spending it on Equatable means the day this model needs a real base class, the equality has to be reworked first:

import 'package:equatable/equatable.dart';

class CartItem extends Equatable {
  const CartItem(this.sku, this.quantity);

  final String sku;
  final int quantity;

  @override
  List<Object?> get props => [sku, quantity];
}

Do

import 'package:equatable/equatable.dart';

class CartItem with EquatableMixin {
  CartItem(this.sku, this.quantity);

  final String sku;
  final int quantity;

  @override
  List<Object?> get props => [sku, quantity];
}

The point: `extends` stays available

With the mixin, the same model can join a hierarchy without giving up equality:

import 'package:equatable/equatable.dart';

abstract class DomainEntity {
  const DomainEntity(this.id);

  final String id;
}

class CartItem extends DomainEntity with EquatableMixin {
  CartItem(super.id, this.sku, this.quantity);

  final String sku;
  final int quantity;

  @override
  List<Object?> get props => [id, sku, quantity];
}

Abstract bases too

An abstract class that extends Equatable passes the same constraint on to every subclass:

import 'package:equatable/equatable.dart';

// Don't — every subclass now has its `extends` slot spent.
abstract class BaseEntity extends Equatable {
  const BaseEntity();
}

// Do
abstract class BaseEntity with EquatableMixin {
  const BaseEntity();
}

Not reported

Only extends Equatable is reported. A class that already uses the mixin, and a class extending something else entirely, are left alone.

See also: equatable package

Configuration

This rule is in no preset, so it is off unless you enable it by name:

rules:
  prefer_equatable_mixin: true

To turn it off again:

rules:
  prefer_equatable_mixin: false

To keep the rule on but skip certain paths, use per-rule exclude.

list_all_equatable_fields — Ensure all fields are listed in Equatable props.
avoid_collection_equality_checks — Avoid comparing collections with == or != as it checks reference equality, not contents.
prefer_overriding_parent_equality — Override == and hashCode when the parent class overrides them.
prefer_async_callback — Use ‘AsyncCallback’ instead of ‘Future<void> Function()’.