In flutter what is the use of hasCode , equal to operator (== operator)

Overview

hashCode

==

Default Behavior (Reference Equality)

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class Point {
  int x, y;
  Point(this.x, this.y);
}

final p1 = Point(1, 2);
final p2 = Point(1, 2);

print(p1 == p2);         // false! Different instances
print(p1.hashCode == p2.hashCode); // false! Different hashes
print(identical(p1, p2)); // false (different objects in memory)

Overriding == and hashCode

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class Point {
  final int x, y;
  const Point(this.x, this.y);

  // Override == for value equality
  @override
  bool operator ==(Object other) {
    if (identical(this, other)) return true; // Same reference
    if (other is! Point) return false;       // Different type
    return x == other.x && y == other.y;    // Compare values
  }

  // Override hashCode to match ==
  @override
  int get hashCode => Object.hash(x, y); // Combine field hashes

  @override
  String toString() => 'Point($x, $y)';
}

void main() {
  final p1 = Point(1, 2);
  final p2 = Point(1, 2);
  final p3 = Point(3, 4);

  print(p1 == p2);        // true ✅
  print(p1 == p3);        // false ✅
  print({p1, p2}.length); // 1 — Set deduplication works!

  // Works in Maps too
  final map = {p1: 'origin'};
  print(map[p2]); // 'origin' — p2 equals p1, finds the key
}

Rules for == and hashCode

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RULE 1: If a == b, then a.hashCode == b.hashCode (MUST)
RULE 2: If a.hashCode == b.hashCode, a == b is NOT guaranteed (hash collision)
RULE 3: hashCode should be consistent during object's lifetime
RULE 4: Override BOTH together — never just one

Using Equatable (Flutter Best Practice)

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import 'package:equatable/equatable.dart';

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

  const User({required this.id, required this.name});

  @override
  List<Object> get props => [id, name]; // Fields for equality
}

// Works automatically
User(id: 1, name: 'Alice') == User(id: 1, name: 'Alice'); // true

Use Cases

{user1, user2}

map[user]

expect(result, expected)

Golden Rule: If you override

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==

, you MUST override

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hashCode

. If two objects are equal (

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a == b

), they must have the same hash code — otherwise

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Set

and

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Map

will break.