What is equatable in flutter ?

Overview

Equatable is a Dart package that simplifies value equality by automatically implementing

==

hashCode

The Problem Without Equatable

Dart uses referential equality by default (compares memory addresses, not values).

dartCopy
class User {
  final String name;
  final int age;

  User(this.name, this.age);
}

void main() {
  final user1 = User('Alice', 25);
  final user2 = User('Alice', 25);

  print(user1 == user2); // false ❌ (different instances)

  // Without overriding ==, BLoC can't detect identical states
  if (previousState == currentState) { /* Never enters! */ }
}

Solution: Equatable Package

Add to

pubspec.yaml

yamlCopy
dependencies:
  equatable: ^2.0.5

Usage:

dartCopy
import 'package:equatable/equatable.dart';

class User extends Equatable {
  final String name;
  final int age;

  const User(this.name, this.age);

  @override
  List<Object?> get props => [name, age]; // Define which fields matter
}

void main() {
  final user1 = User('Alice', 25);
  final user2 = User('Alice', 25);

  print(user1 == user2); // true ✅ (same values)
}

How It Works

Equatable overrides

==

hashCode

dartCopy
// What Equatable does internally (simplified):
@override
bool operator ==(Object other) {
  if (identical(this, other)) return true;
  return other is User &&
         other.name == name &&
         other.age == age;
}

@override
int get hashCode => name.hashCode ^ age.hashCode;

With BLoC State Management

Equatable prevents unnecessary widget rebuilds.

dartCopy
// ❌ Without Equatable
class CounterState {
  final int count;
  CounterState(this.count);
}

// BLoC emits new state
emit(CounterState(5));
emit(CounterState(5)); // ❌ Rebuilds widget even though count is same!

// ✅ With Equatable
class CounterState extends Equatable {
  final int count;
  const CounterState(this.count);

  @override
  List<Object?> get props => [count];
}

emit(CounterState(5));
emit(CounterState(5)); // ✅ No rebuild (Equatable detects same value)

Advanced Features

Ignore Specific Fields

dartCopy
class User extends Equatable {
  final String id;
  final String name;
  final DateTime lastLogin; // Don't compare this

  const User(this.id, this.name, this.lastLogin);

  @override
  List<Object?> get props => [id, name]; // lastLogin not included
}

Nullable Fields

dartCopy
class Profile extends Equatable {
  final String username;
  final String? bio; // Nullable

  const Profile(this.username, this.bio);

  @override
  List<Object?> get props => [username, bio]; // Handles nulls
}

Stringify (Debugging)

dartCopy
class User extends Equatable {
  final String name;
  final int age;

  const User(this.name, this.age);

  @override
  List<Object?> get props => [name, age];

  @override
  bool get stringify => true; // Auto-generate toString()
}

print(User('Alice', 25)); // User(Alice, 25) ✅

With Collections

dartCopy
class TaskList extends Equatable {
  final List<String> tasks;

  const TaskList(this.tasks);

  @override
  List<Object?> get props => [tasks];
}

final list1 = TaskList(['a', 'b']);
final list2 = TaskList(['a', 'b']);
print(list1 == list2); // true ✅ (deep equality)

Comparison Table

==

props

hashCode

Best Practices

dartCopy
// ✅ Use const constructors with Equatable
class User extends Equatable {
  final String name;
  const User(this.name); // const = compile-time constant

  @override
  List<Object?> get props => [name];
}

// ✅ Include all relevant fields in props
@override
List<Object?> get props => [id, name, email]; // All important fields

// ❌ Don't include derived/computed fields
class User extends Equatable {
  final String firstName;
  final String lastName;
  String get fullName => '$firstName $lastName'; // Don't add to props

  @override
  List<Object?> get props => [firstName, lastName]; // Only stored fields
}

When to Use

• ✅ BLoC states/events — Prevents duplicate state emissions
• ✅ Riverpod providers — Correctly detects state changes
• ✅ Data models — User, Product, etc. (value objects)
• ✅ Testing — Compare expected vs actual results

Learn more: Equatable Package