werediver/sum_types.dart

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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.

Example

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(),
      );
}

Features

Core:

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

Sugar:

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

Trivia:

• [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)))

Development

Find the upcoming development plans in the project planner.