How to override the comparison operation for objects in Flutter?

To override the comparison operator == and hashCode, you need to implement them in the class. The equatable package is often used for this purpose.

import 'package:equatable/equatable.dart';

class MyObject extends Equatable {
  final int id;
  final String name;

  const MyObject(this.id, this.name);

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

Without equatable, the implementation would look like this:

class MyObject {
  final int id;
  final String name;

  const MyObject(this.id, this.name);

  @override
  bool operator ==(Object other) {
    if (identical(this, other)) return true;

    return other is MyObject &&
        other.id == id &&
        other.name == name;
  }

  @override
  int get hashCode => id.hashCode ^ name.hashCode;
}

When overriding ==, it is always necessary to override hashCode as well, to maintain the contract between them: if two objects are equal according to ==, their hash codes must be equal. The reverse is not necessarily true.

Usage:

final obj1 = MyObject(1, 'Test');
final obj2 = MyObject(1, 'Test');
final obj3 = MyObject(2, 'Other');

print(obj1 == obj2); // Output: true
print(obj1 == obj3); // Output: false