builtvalue

Built_value is a Dart library that provides immutable value types through a code-generated builder pattern. It emphasizes strong typing, value equality, and safe serialization for data models used in Flutter and Dart apps. The library also offers immutable collections via built_collection, enabling deep immutability for lists, maps, and sets.

Usage centers on declaring an abstract class that implements Built<MyClass, MyClassBuilder>, listing fields as getters, and providing a private constructor plus a factory that delegates to _$MyClass. A generated part file is required, typically named my_class.g.dart. The build system via build_runner creates the concrete implementation. The approach yields robust, type-safe models with consistent equality, hash codes, and string representations.

Creating and updating instances uses a builder. For example, you construct with MyClass((b)=> b..name='Alice'..age=30). To modify, use rebuild or toBuilder: var updated = person.rebuild((b)=> b..age = 31); or var draft = person.toBuilder(); These operations preserve immutability while offering ergonomic mutation.

Serialization is supported through Serializers and generated serializers. You typically expose a serializer for your type and register it in a central Serializers collection, enabling JSON encoding and decoding with standard hooks.

Built_value integrates with built_collection for immutable collections and can improve correctness in large state-heavy Dart apps, at the cost of an initial learning curve and an extra code-generation step.