Dart + Bloc + Freezed (Unions and Map to State)

dart_bloc_freezed.dart

import 'package:bloc/bloc.dart';
import 'package:freezed_annotation/freezed_annotation.dart';

part 'counter_bloc.freezed.dart';

class CounterBloc extends Bloc<CounterEvent, CounterState> {
  CounterBloc() : super(CounterState.value(0));

  @override
  Stream<CounterState> mapEventToState(CounterEvent event) async* {
    yield* event.map<Stream<CounterState>>(
      increment: (val) async* {
        yield CounterState.value(state.value + 1);
      },
      decrement: (val) async* {
        yield CounterState.value(state.value - 1);
      },
      update: (val) async* {
        yield CounterState.value(val.value);
      },
      reset: (val) async* {
        yield CounterState.value(0);
      },
    );
  }
}

@freezed
abstract class CounterEvent with _$CounterEvent {
  const factory CounterEvent.decrement() = CounterDecrement;
  const factory CounterEvent.increment() = CounterIncrement;
  const factory CounterEvent.update(int value) = CounterUpdate;
  const factory CounterEvent.reset() = CounterReset;
}

@freezed
abstract class CounterState with _$CounterState {
  const factory CounterState.value(int value) = CounterReady;
}