sum_types and sum_types_generator packages together define a code generator enabling sum-types in Dart.

NOTE: v0.2.0 is a major update with backward-incompatible changes.

In example/lib/src/ you can find a few sum-type declarations and the code generated for them.

This one models the natural numbers (with zero):

import 'package:meta/meta.dart';
import 'package:sum_types/sum_types.dart';

@SumType()
class Nat extends _$Nat {
  const Nat.zero() : super(zero: const Unit());
  const Nat.next(Nat value) : super(next: value);

  Nat operator +(Nat other) => this.iswitch(
        zero: () => other,
        next: (next) => Nat.next(next + other),
      );

  int toInt() => this.iswitch(
        zero: () => 0,
        next: (next) => 1 + next.toInt(),
      );
}

Core:

• Const case-constructors (const Nat.zero())
• Extensible sum-types (Nat.toInt())
• Nested sum-types
• Recursive sum-types (Case<_Nat>(name: "next") → Nat.next(Nat.zero()))
• Generic sum-types (Either<Left, Right>)
• Exhaustive in-line iswitch
• Inexhaustive in-line iswitcho (with otherwise: case)

Sugar:

• No-payload cases (Case<void>(name: "zero") → Nat.zero())
• Default case-names (Case<String>() → JSON.string("some"))

Trivia:

• Equality test
• Hash function
• To string conversion

Serialization-deserialization support through product-types interoperability:

• Deserialization support (NatRecord<Self>, Nat.load<T extends NatRecord<T>>(T rec))
• Serialization support (Nat.dump<T>(T Function({Unit zero, T next} make)))

Find the upcoming development plans in the project planner.