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Vishnu C Prasad
Vishnu C Prasad

Posted on • Originally published at vishnucprasad.Medium

Understanding the Significance of the Freezed Package in Flutter


Flutter, Google’s open-source UI software development toolkit, has gained immense popularity for its ability to create natively compiled applications for mobile, web, and desktop from a single codebase. As developers dive into the Flutter ecosystem, they encounter various tools and packages that enhance productivity and code maintainability. One such package that has become increasingly popular is the Freezed package. In this article, we will explore why developers use the Freezed package in Flutter and how it contributes to more robust and efficient code.

Immutability in Dart

Dart, the programming language used in Flutter development, supports object-oriented programming and provides features like classes and inheritance. However, Dart does not have built-in support for immutable objects. Immutability is a crucial concept in software development as it helps prevent unintended side effects and makes code easier to reason about.

The Need for Immutable Objects

In Flutter applications, maintaining state is a critical aspect of the development process. Immutable objects, once created, cannot be changed. Instead of modifying existing objects, developers create new ones with the desired changes. This approach helps in managing the state of an application more effectively and reduces the chances of bugs caused by unexpected changes.

Introducing Freezed Package

The Freezed package, developed by Rémi Rousselet, provides a solution for generating immutable classes with ease. It is particularly well-suited for working with data models and value objects in Flutter applications. Freezed uses code generation to create boilerplate code for immutable classes, reducing the amount of manual coding required from developers.

Key Features of Freezed

1. freezed Annotation

Developers can annotate their Dart classes with @freezed to instruct the Freezed package to generate the necessary code for immutability.

abstract class User with _$User {
  const factory User({
    required String id,
    required String name,
    required int age,
  }) = _User;
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2. Immutable Classes:

The @freezed annotation generates immutable classes automatically. These classes include methods for equality comparisons (== and hashCode), making them suitable for use in collections and comparisons.

3. Union Classes:

Freezed supports union classes, allowing developers to define a closed set of possible states for a class. This can be especially beneficial in managing application state.

abstract class AppState with _$AppState {
  const factory AppState.initial() = _Initial;
  const factory AppState.loading() = _Loading;
  const factory AppState.loaded(List<User> users) = _Loaded;
  const factory AppState.error(String message) = _Error;
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4. Pattern Matching:

Freezed generates pattern-matching methods for union classes, making it easy to handle different states without the need for boilerplate code.

void handleAppState(AppState state) {
    initial: () => print('Initial state'),
    loading: () => print('Loading state'),
    loaded: (users) => print('Loaded state with ${users.length} users'),
    error: (message) => print('Error state: $message'),
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5. CopyWith Method

Freezed generates a copyWith method for each class, making it convenient to create copies of objects with modified properties. This is particularly useful when updating the state of an object without changing its original instance.

// Creating an instance of the User class
final user = User(id: '1', name: 'John Doe', age: 25);

// Using copyWith to create a new instance with updated properties
final updatedUser = user.copyWith(name: 'Jane Doe', age: 26);
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Advantages of Using Freezed

1. Reduced Boilerplate Code:

Freezed significantly reduces the amount of boilerplate code developers need to write for immutable classes. This leads to cleaner and more maintainable code.

2. Type Safety:

The generated code by Freezed ensures type safety, reducing the possibility of runtime errors related to state changes.

3. Improved Developer Productivity:

With less manual coding and automatic generation of necessary methods, developers can focus more on application logic and features, enhancing overall productivity.


The Freezed package in Flutter addresses the need for immutability in Dart, providing developers with a powerful tool for creating robust and efficient code. By automating the generation of boilerplate code for immutable classes and supporting union classes, Freezed enhances code maintainability and reduces the possibility of bugs related to state management. As Flutter continues to evolve, tools like Freezed contribute to a more streamlined and enjoyable development experience, making it a valuable addition to the toolkit of Flutter developers.

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