Features

By annotating the class, the code required for the "Value Class" is automatically generated.

Inspired by json_serializable and freezed.

Getting started

Flutter project:

flutter pub add value_annotation
flutter pub add --dev build_runner
flutter pub add --dev value_class

flutter pub get

Dart project:

dart pub add value_annotation
dart pub add --dev build_runner
dart pub add --dev value_class

dart pub get

Usage

1. Create class

import 'package:value_annotation/value_annotation.dart';

part 'example.value.dart';

@valueClass
class Example with _$Example {
  const factory Example(String value) = _Example;

  const factory Example.fromJson(String value) = _Example;
}

2. Run generator

Flutter project:

flutter pub run build_runner build

Dart project:

dart run build_runner build

Asserts

Similar to freezed, you can use @Assert to add assert(...) statement to the generated class.

Note
Unlike freezed, the first argument of @Assert is a Function instead of a String to reduce typos. Therefore, the constructor cannot be given the const modifier.

import 'package:value_annotation/value_annotation.dart';

part 'email.value.dart';

@valueClass
class Email with _$Email {
  @Assert(_checkNotEmpty, 'Email cannot be empty')
  @Assert(_checkFormat, 'Email format is invalid')
  factory Email(String value) = _Email;
}

bool _checkNotEmpty(String value) => value.isNotEmpty;
bool _checkFormat(String value) => value.contains(RegExp(r'^.+@\S+\.\S+$'));

Combination

This package supports the combination of json_serializable and freezed.

See the example directory.

import 'package:value_annotation/value_annotation.dart';

part 'email.value.dart';

@valueClass
class Email with _$Email {
  @Assert(_checkNotEmpty, 'Email cannot be empty')
  @Assert(_checkFormat, 'Email format is invalid')
  factory Email(String value) = _Email;

  factory Email.fromJson(String value) = _Email;
}

bool _checkNotEmpty(String value) => value.isNotEmpty;
bool _checkFormat(String value) => value.contains(RegExp(r'^.+@\S+\.\S+$'));

import 'package:example/model/email.dart';
import 'package:freezed_annotation/freezed_annotation.dart';

part 'person.freezed.dart';

part 'person.g.dart';

@freezed
class Person with _$Person {
  const factory Person({
    required Email email,
  }) = _Person;

  factory Person.fromJson(Map<String, Object?> json) => _$PersonFromJson(json);
}

import 'dart:convert';

import 'package:example/model/email.dart';
import 'package:example/model/person.dart';
import 'package:simple_logger/simple_logger.dart';

void main() {
  final personBefore = Person(email: Email('example@gmail.com'));
  final encoded = jsonEncode(personBefore);

  final decoded = jsonDecode(encoded) as Map<String, dynamic>;
  final personAfter = Person.fromJson(decoded);

  SimpleLogger()
    ..info('Encoded: $encoded')
    ..info('Decoded: $personAfter')
    ..info('Equals: ${personBefore == personAfter}');
}

Executing main() will output following log.

👻 INFO 2022-08-05 01:20:40.412135 [caller info not available] Encoded: {"email":"example@gmail.com"}
👻 INFO 2022-08-05 01:20:40.414220 [caller info not available] Decoded: Person(email: Email(value: example@gmail.com))
👻 INFO 2022-08-05 01:20:40.414812 [caller info not available] Equals: true

Process finished with exit code 0

Supported types

The following Types in the dart:core library are supported:

• String
• bool
• int
• double
• num

More types will be supported in the future.

Under consideration

• BigInt
• Enum
• Iterable
• List
• Map
• Set
• Uri
• DateTime
• Duration
• Object that has fromJson() and toJson()

How to contribute

You should follow our Code of Conduct.

See Contributor Guide for contributing conventions.

Contributors

blendthink