Is it possible to generate class methods?

[guilhermearaujo]

Today we use freezed to generate some class methods like this:

import 'package:freezed_annotation/freezed_annotation.dart';

part 'something_state.freezed.dart';

@freezed
class SomethingState with _$SomethingState {
  const factory SomethingState.initial() = _Initial;
  const factory SomethingState.loading() = _Loading;
  const factory SomethingState.invalid(String errorMessage) = _Invalid;
}

and freezed outputs:

// coverage:ignore-file
// GENERATED CODE - DO NOT MODIFY BY HAND
// ignore_for_file: type=lint
// ignore_for_file: unused_element, deprecated_member_use, deprecated_member_use_from_same_package, use_function_type_syntax_for_parameters, unnecessary_const, avoid_init_to_null, invalid_override_different_default_values_named, prefer_expression_function_bodies, annotate_overrides, invalid_annotation_target, unnecessary_question_mark

part of 'something_state.dart';

// **************************************************************************
// FreezedGenerator
// **************************************************************************

T _$identity<T>(T value) => value;

final _privateConstructorUsedError = UnsupportedError(
    'It seems like you constructed your class using `MyClass._()`. This constructor is only meant to be used by freezed and you are not supposed to need it nor use it.\nPlease check the documentation here for more information: https://github.com/rrousselGit/freezed#custom-getters-and-methods');

/// @nodoc
mixin _$SomethingState {
  @optionalTypeArgs
  TResult when<TResult extends Object?>({
    required TResult Function() initial,
    required TResult Function() loading,
    required TResult Function(String errorMessage) invalid,
  }) =>
      throw _privateConstructorUsedError;
  @optionalTypeArgs
  TResult? whenOrNull<TResult extends Object?>({
    TResult? Function()? initial,
    TResult? Function()? loading,
    TResult? Function(String errorMessage)? invalid,
  }) =>
      throw _privateConstructorUsedError;
  @optionalTypeArgs
  TResult maybeWhen<TResult extends Object?>({
    TResult Function()? initial,
    TResult Function()? loading,
    TResult Function(String errorMessage)? invalid,
    required TResult orElse(),
  }) =>
      throw _privateConstructorUsedError;
  @optionalTypeArgs
  TResult map<TResult extends Object?>({
    required TResult Function(_Initial value) initial,
    required TResult Function(_Loading value) loading,
    required TResult Function(_Invalid value) invalid,
  }) =>
      throw _privateConstructorUsedError;
  @optionalTypeArgs
  TResult? mapOrNull<TResult extends Object?>({
    TResult? Function(_Initial value)? initial,
    TResult? Function(_Loading value)? loading,
    TResult? Function(_Invalid value)? invalid,
  }) =>
      throw _privateConstructorUsedError;
  @optionalTypeArgs
  TResult maybeMap<TResult extends Object?>({
    TResult Function(_Initial value)? initial,
    TResult Function(_Loading value)? loading,
    TResult Function(_Invalid value)? invalid,
    required TResult orElse(),
  }) =>
      throw _privateConstructorUsedError;
}

/// @nodoc
abstract class $SomethingStateCopyWith<$Res> {
  factory $SomethingStateCopyWith(
          SomethingState value, $Res Function(SomethingState) then) =
      _$SomethingStateCopyWithImpl<$Res, SomethingState>;
}

/// @nodoc
class _$SomethingStateCopyWithImpl<$Res, $Val extends SomethingState>
    implements $SomethingStateCopyWith<$Res> {
  _$SomethingStateCopyWithImpl(this._value, this._then);

  // ignore: unused_field
  final $Val _value;
  // ignore: unused_field
  final $Res Function($Val) _then;
}

/// @nodoc
abstract class _$$InitialImplCopyWith<$Res> {
  factory _$$InitialImplCopyWith(
          _$InitialImpl value, $Res Function(_$InitialImpl) then) =
      __$$InitialImplCopyWithImpl<$Res>;
}

/// @nodoc
class __$$InitialImplCopyWithImpl<$Res>
    extends _$SomethingStateCopyWithImpl<$Res, _$InitialImpl>
    implements _$$InitialImplCopyWith<$Res> {
  __$$InitialImplCopyWithImpl(
      _$InitialImpl _value, $Res Function(_$InitialImpl) _then)
      : super(_value, _then);
}

/// @nodoc

class _$InitialImpl implements _Initial {
  const _$InitialImpl();

  @override
  String toString() {
    return 'SomethingState.initial()';
  }

  @override
  bool operator ==(Object other) {
    return identical(this, other) ||
        (other.runtimeType == runtimeType && other is _$InitialImpl);
  }

  @override
  int get hashCode => runtimeType.hashCode;

  @override
  @optionalTypeArgs
  TResult when<TResult extends Object?>({
    required TResult Function() initial,
    required TResult Function() loading,
    required TResult Function(String errorMessage) invalid,
  }) {
    return initial();
  }

  @override
  @optionalTypeArgs
  TResult? whenOrNull<TResult extends Object?>({
    TResult? Function()? initial,
    TResult? Function()? loading,
    TResult? Function(String errorMessage)? invalid,
  }) {
    return initial?.call();
  }

  @override
  @optionalTypeArgs
  TResult maybeWhen<TResult extends Object?>({
    TResult Function()? initial,
    TResult Function()? loading,
    TResult Function(String errorMessage)? invalid,
    required TResult orElse(),
  }) {
    if (initial != null) {
      return initial();
    }
    return orElse();
  }

  @override
  @optionalTypeArgs
  TResult map<TResult extends Object?>({
    required TResult Function(_Initial value) initial,
    required TResult Function(_Loading value) loading,
    required TResult Function(_Invalid value) invalid,
  }) {
    return initial(this);
  }

  @override
  @optionalTypeArgs
  TResult? mapOrNull<TResult extends Object?>({
    TResult? Function(_Initial value)? initial,
    TResult? Function(_Loading value)? loading,
    TResult? Function(_Invalid value)? invalid,
  }) {
    return initial?.call(this);
  }

  @override
  @optionalTypeArgs
  TResult maybeMap<TResult extends Object?>({
    TResult Function(_Initial value)? initial,
    TResult Function(_Loading value)? loading,
    TResult Function(_Invalid value)? invalid,
    required TResult orElse(),
  }) {
    if (initial != null) {
      return initial(this);
    }
    return orElse();
  }
}

abstract class _Initial implements SomethingState {
  const factory _Initial() = _$InitialImpl;
}

/// @nodoc
abstract class _$$LoadingImplCopyWith<$Res> {
  factory _$$LoadingImplCopyWith(
          _$LoadingImpl value, $Res Function(_$LoadingImpl) then) =
      __$$LoadingImplCopyWithImpl<$Res>;
}

/// @nodoc
class __$$LoadingImplCopyWithImpl<$Res>
    extends _$SomethingStateCopyWithImpl<$Res, _$LoadingImpl>
    implements _$$LoadingImplCopyWith<$Res> {
  __$$LoadingImplCopyWithImpl(
      _$LoadingImpl _value, $Res Function(_$LoadingImpl) _then)
      : super(_value, _then);
}

/// @nodoc

class _$LoadingImpl implements _Loading {
  const _$LoadingImpl();

  @override
  String toString() {
    return 'SomethingState.loading()';
  }

  @override
  bool operator ==(Object other) {
    return identical(this, other) ||
        (other.runtimeType == runtimeType && other is _$LoadingImpl);
  }

  @override
  int get hashCode => runtimeType.hashCode;

  @override
  @optionalTypeArgs
  TResult when<TResult extends Object?>({
    required TResult Function() initial,
    required TResult Function() loading,
    required TResult Function(String errorMessage) invalid,
  }) {
    return loading();
  }

  @override
  @optionalTypeArgs
  TResult? whenOrNull<TResult extends Object?>({
    TResult? Function()? initial,
    TResult? Function()? loading,
    TResult? Function(String errorMessage)? invalid,
  }) {
    return loading?.call();
  }

  @override
  @optionalTypeArgs
  TResult maybeWhen<TResult extends Object?>({
    TResult Function()? initial,
    TResult Function()? loading,
    TResult Function(String errorMessage)? invalid,
    required TResult orElse(),
  }) {
    if (loading != null) {
      return loading();
    }
    return orElse();
  }

  @override
  @optionalTypeArgs
  TResult map<TResult extends Object?>({
    required TResult Function(_Initial value) initial,
    required TResult Function(_Loading value) loading,
    required TResult Function(_Invalid value) invalid,
  }) {
    return loading(this);
  }

  @override
  @optionalTypeArgs
  TResult? mapOrNull<TResult extends Object?>({
    TResult? Function(_Initial value)? initial,
    TResult? Function(_Loading value)? loading,
    TResult? Function(_Invalid value)? invalid,
  }) {
    return loading?.call(this);
  }

  @override
  @optionalTypeArgs
  TResult maybeMap<TResult extends Object?>({
    TResult Function(_Initial value)? initial,
    TResult Function(_Loading value)? loading,
    TResult Function(_Invalid value)? invalid,
    required TResult orElse(),
  }) {
    if (loading != null) {
      return loading(this);
    }
    return orElse();
  }
}

abstract class _Loading implements SomethingState {
  const factory _Loading() = _$LoadingImpl;
}

/// @nodoc
abstract class _$$InvalidImplCopyWith<$Res> {
  factory _$$InvalidImplCopyWith(
          _$InvalidImpl value, $Res Function(_$InvalidImpl) then) =
      __$$InvalidImplCopyWithImpl<$Res>;
  @useResult
  $Res call({String errorMessage});
}

/// @nodoc
class __$$InvalidImplCopyWithImpl<$Res>
    extends _$SomethingStateCopyWithImpl<$Res, _$InvalidImpl>
    implements _$$InvalidImplCopyWith<$Res> {
  __$$InvalidImplCopyWithImpl(
      _$InvalidImpl _value, $Res Function(_$InvalidImpl) _then)
      : super(_value, _then);

  @pragma('vm:prefer-inline')
  @override
  $Res call({
    Object? errorMessage = null,
  }) {
    return _then(_$InvalidImpl(
      null == errorMessage
          ? _value.errorMessage
          : errorMessage // ignore: cast_nullable_to_non_nullable
              as String,
    ));
  }
}

/// @nodoc

class _$InvalidImpl implements _Invalid {
  const _$InvalidImpl(this.errorMessage);

  @override
  final String errorMessage;

  @override
  String toString() {
    return 'SomethingState.invalid(errorMessage: $errorMessage)';
  }

  @override
  bool operator ==(Object other) {
    return identical(this, other) ||
        (other.runtimeType == runtimeType &&
            other is _$InvalidImpl &&
            (identical(other.errorMessage, errorMessage) ||
                other.errorMessage == errorMessage));
  }

  @override
  int get hashCode => Object.hash(runtimeType, errorMessage);

  @JsonKey(ignore: true)
  @override
  @pragma('vm:prefer-inline')
  _$$InvalidImplCopyWith<_$InvalidImpl> get copyWith =>
      __$$InvalidImplCopyWithImpl<_$InvalidImpl>(this, _$identity);

  @override
  @optionalTypeArgs
  TResult when<TResult extends Object?>({
    required TResult Function() initial,
    required TResult Function() loading,
    required TResult Function(String errorMessage) invalid,
  }) {
    return invalid(errorMessage);
  }

  @override
  @optionalTypeArgs
  TResult? whenOrNull<TResult extends Object?>({
    TResult? Function()? initial,
    TResult? Function()? loading,
    TResult? Function(String errorMessage)? invalid,
  }) {
    return invalid?.call(errorMessage);
  }

  @override
  @optionalTypeArgs
  TResult maybeWhen<TResult extends Object?>({
    TResult Function()? initial,
    TResult Function()? loading,
    TResult Function(String errorMessage)? invalid,
    required TResult orElse(),
  }) {
    if (invalid != null) {
      return invalid(errorMessage);
    }
    return orElse();
  }

  @override
  @optionalTypeArgs
  TResult map<TResult extends Object?>({
    required TResult Function(_Initial value) initial,
    required TResult Function(_Loading value) loading,
    required TResult Function(_Invalid value) invalid,
  }) {
    return invalid(this);
  }

  @override
  @optionalTypeArgs
  TResult? mapOrNull<TResult extends Object?>({
    TResult? Function(_Initial value)? initial,
    TResult? Function(_Loading value)? loading,
    TResult? Function(_Invalid value)? invalid,
  }) {
    return invalid?.call(this);
  }

  @override
  @optionalTypeArgs
  TResult maybeMap<TResult extends Object?>({
    TResult Function(_Initial value)? initial,
    TResult Function(_Loading value)? loading,
    TResult Function(_Invalid value)? invalid,
    required TResult orElse(),
  }) {
    if (invalid != null) {
      return invalid(this);
    }
    return orElse();
  }
}

abstract class _Invalid implements SomethingState {
  const factory _Invalid(final String errorMessage) = _$InvalidImpl;

  String get errorMessage;
  @JsonKey(ignore: true)
  _$$InvalidImplCopyWith<_$InvalidImpl> get copyWith =>
      throw _privateConstructorUsedError;
}

Is it possible to use genq to do the same?

[jankuss]

It is not possible as of now.

I'm a bit torn on this feature - I think the syntactic sugar would be a very nice addition, as the alternative for sealed classes is quite verbose.

I'm not sure though if we should generate the map, maybeMap etc. As of Dart 3.0, the necessity for these methods is questionable, as pattern matching & sealed classes exists now. If we include it, it will definetly be an opt in feature.

[BWhiteApps]

I personally don't see a need for map, maybeMap, maybeWhen... freezed is already going away from those. But being able to generate sealed classes and unions with the freezed syntax would be huge.

[guilhermearaujo]

That example is from an older project I started working on recently, I honestly don't even know if all that generated code is really necessary or if just a piece of it should be enough.

Interesting, I was not familiar with sealed classes. That may actually work, but I need to test it.