Value brings simple way of defining Value Objects in Dart. It uses power of Freezed package and its Union types.

The main reason to use Value is to wrap simple types like String and num into meaningful types that can be easily validated.

Some commonly used value types are provided by the library:

• EmailAddress
• Url

Getting started

Add to your pubspec.yaml:

dependencies:
  value:
    git: https://github.com/adriank/value.git

Usage

Using Value turns this code:

  final emailAddress = 'me@example.com';
  print(emailAddress.runtimeType); // String

into a meaningful EmailAddress type that can be validated:

  final emailAddress = EmailAddress('me@example.com');
  print(emailAddress.runtimeType); // String
  print(emailAddress.isValid); // true
  final otherEmailAddress = EmailAddress('example.com');
  print(invalidEmailAddress().when(
    (emailAddress) => 'Valid! $emailAddress',
    invalidEmail: (invalidEmail) => 'Not valid! $invalidEmail',
  )); // 'Not valid! example.com'

Check example directory to learn more:

• Using EmailAddress
• Creating your own value type

Additional resources

Read about making invalid state unrepresentable: Making invalid state unrepresentable by Khalil Stemmler Why we should use exhaustive checks by Nicholas Fahrenkrog