Build Status sum_types version sum_types_generator version

sum_types and sum_types_generator

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';

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

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

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



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


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


  • x Equality test
  • x Hash function
  • x To string conversion

Serialization-deserialization support through product-types interoperability:

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


Find the upcoming development plans in the project planner.