mobile bluesky app made with flutter
lazurite.stormlightlabs.org/
mobile
bluesky
flutter
feat: nullable copyWith pattern for state management
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-63
+40
docs/copywith.md
+40
docs/copywith.md
···
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# Nullable `copyWith` Rule
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## Problem
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A common state bug occurs when `copyWith` uses `field ?? this.field` for nullable fields.
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That pattern cannot distinguish:
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- "keep current value"
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- "set this field to null"
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This breaks flows where `null` is meaningful (for example clearing cursors, `likeUri`, `repostUri`, or `errorMessage`).
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## Required Pattern
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For nullable fields in immutable state objects, use a sentinel parameter default:
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```dart
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static const Object _unset = Object();
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State copyWith({
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Object? nullableField = _unset,
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}) {
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return State(
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nullableField: identical(nullableField, _unset)
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? this.nullableField
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: nullableField as String?,
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);
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}
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```
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## Where Applied
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- `SearchState.copyWith` (cursor and nullable metadata fields)
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- `FeedState.copyWith` (cursor and error fields)
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- `PostActionState.copyWith` (`likeUri`, `repostUri`, `error`)
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## Review Checklist
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- If a field is nullable and needs to be clearable, do not use `??` in `copyWith`.
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- Add/keep tests that assert nullable fields can be explicitly cleared to `null`.
+15
-15
lib/features/feed/bloc/feed_state.dart
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lib/features/feed/bloc/feed_state.dart
···
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const FeedState.error(String message) : this._(status: FeedStatus.error, errorMessage: message);
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static const Object _unset = Object();
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final FeedStatus status;
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final String? actor;
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final List<FeedViewPost> posts;
···
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FeedStatus? status,
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String? actor,
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List<FeedViewPost>? posts,
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String? cursor,
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String? errorMessage,
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Object? cursor = _unset,
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Object? errorMessage = _unset,
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FeedFilter? filter,
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bool? hasMore,
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bool? isLoadingMore,
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bool? isRefreshing,
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}) {
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return FeedState._(
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status: status ?? this.status,
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actor: actor ?? this.actor,
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posts: posts ?? this.posts,
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cursor: cursor ?? this.cursor,
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errorMessage: errorMessage ?? this.errorMessage,
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filter: filter ?? this.filter,
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hasMore: hasMore ?? this.hasMore,
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isLoadingMore: isLoadingMore ?? this.isLoadingMore,
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isRefreshing: isRefreshing ?? this.isRefreshing,
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);
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}
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}) => FeedState._(
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status: status ?? this.status,
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actor: actor ?? this.actor,
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posts: posts ?? this.posts,
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cursor: identical(cursor, _unset) ? this.cursor : cursor as String?,
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errorMessage: identical(errorMessage, _unset) ? this.errorMessage : errorMessage as String?,
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filter: filter ?? this.filter,
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hasMore: hasMore ?? this.hasMore,
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isLoadingMore: isLoadingMore ?? this.isLoadingMore,
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isRefreshing: isRefreshing ?? this.isRefreshing,
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);
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@override
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List<Object?> get props => [status, actor, posts, cursor, errorMessage, filter, hasMore, isLoadingMore, isRefreshing];
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lib/features/feed/cubit/post_action_cubit.dart
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lib/features/feed/cubit/post_action_cubit.dart
···
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this.isDeleted = false,
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this.error,
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});
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// Sentinel used by copyWith to distinguish "keep existing value"
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// from an explicit null assignment for nullable fields.
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static const Object _unset = Object();
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final String postUri;
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final bool isLiked;
···
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bool? isReposted,
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int? likeCount,
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int? repostCount,
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String? likeUri,
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String? repostUri,
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Object? likeUri = _unset,
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Object? repostUri = _unset,
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bool? isLoadingLike,
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bool? isLoadingRepost,
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bool? isDeleted,
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String? error,
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}) {
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return PostActionState(
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postUri: postUri,
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isLiked: isLiked ?? this.isLiked,
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isReposted: isReposted ?? this.isReposted,
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likeCount: likeCount ?? this.likeCount,
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repostCount: repostCount ?? this.repostCount,
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likeUri: likeUri ?? this.likeUri,
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repostUri: repostUri ?? this.repostUri,
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isLoadingLike: isLoadingLike ?? this.isLoadingLike,
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isLoadingRepost: isLoadingRepost ?? this.isLoadingRepost,
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isDeleted: isDeleted ?? this.isDeleted,
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error: error ?? this.error,
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);
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}
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Object? error = _unset,
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}) => PostActionState(
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postUri: postUri,
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isLiked: isLiked ?? this.isLiked,
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isReposted: isReposted ?? this.isReposted,
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likeCount: likeCount ?? this.likeCount,
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repostCount: repostCount ?? this.repostCount,
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likeUri: identical(likeUri, _unset) ? this.likeUri : likeUri as String?,
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repostUri: identical(repostUri, _unset) ? this.repostUri : repostUri as String?,
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isLoadingLike: isLoadingLike ?? this.isLoadingLike,
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isLoadingRepost: isLoadingRepost ?? this.isLoadingRepost,
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isDeleted: isDeleted ?? this.isDeleted,
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error: identical(error, _unset) ? this.error : error as String?,
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);
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@override
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List<Object?> get props => [
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-1
lib/features/feed/presentation/post_thread_screen.dart
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-1
lib/features/feed/presentation/post_thread_screen.dart
···
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import 'package:go_router/go_router.dart';
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import 'package:intl/intl.dart';
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import 'package:lazurite/core/logging/app_logger.dart';
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import 'package:lazurite/features/compose/presentation/compose_route_args.dart';
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import 'package:lazurite/features/connectivity/cubit/connectivity_cubit.dart';
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import 'package:lazurite/features/compose/presentation/compose_route_args.dart';
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import 'package:lazurite/features/feed/cubit/post_action_cache.dart';
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import 'package:lazurite/features/feed/cubit/post_action_cubit.dart';
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import 'package:lazurite/features/feed/cubit/post_thread_cubit.dart';
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import 'package:lazurite/features/feed/cubit/saved_posts_cubit.dart';
···
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repostCount: post.repostCount ?? 0,
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likeUri: viewer?.like?.toString(),
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repostUri: viewer?.repost?.toString(),
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cache: context.read<PostActionCache>(),
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),
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child: BlocListener<PostActionCubit, PostActionState>(
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listenWhen: (previous, current) => previous.error != current.error && current.error != null,
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lib/features/search/bloc/search_state.dart
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lib/features/search/bloc/search_state.dart
···
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top,
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latest;
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factory SearchSort.fromString(String value) {
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return switch (value) {
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'top' => SearchSort.top,
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_ => SearchSort.latest,
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};
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}
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factory SearchSort.fromString(String value) => switch (value) {
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'top' => SearchSort.top,
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_ => SearchSort.latest,
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};
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}
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extension SearchSortLabel on SearchSort {
···
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const SearchState.error({required String query, required String message})
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: this._(status: SearchStatus.error, query: query, errorMessage: message);
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static const Object _unset = Object();
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final SearchStatus status;
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final String query;
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final SearchTab currentTab;
···
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List<ProfileView>? actors,
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List<GeneratorView>? feeds,
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List<StarterPackViewBasic>? starterPacks,
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String? cursor,
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String? starterPacksCursor,
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int? hitsTotal,
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String? errorMessage,
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Object? cursor = _unset,
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Object? starterPacksCursor = _unset,
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Object? hitsTotal = _unset,
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Object? errorMessage = _unset,
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bool? isLoadingMore,
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List<ProfileViewBasic>? typeaheadActors,
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List<SearchHistoryEntry>? searchHistory,
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}) {
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return SearchState._(
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status: status ?? this.status,
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query: query ?? this.query,
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currentTab: currentTab ?? this.currentTab,
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currentSort: currentSort ?? this.currentSort,
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posts: posts ?? this.posts,
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actors: actors ?? this.actors,
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feeds: feeds ?? this.feeds,
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starterPacks: starterPacks ?? this.starterPacks,
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cursor: cursor ?? this.cursor,
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starterPacksCursor: starterPacksCursor ?? this.starterPacksCursor,
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hitsTotal: hitsTotal ?? this.hitsTotal,
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errorMessage: errorMessage ?? this.errorMessage,
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isLoadingMore: isLoadingMore ?? this.isLoadingMore,
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typeaheadActors: typeaheadActors ?? this.typeaheadActors,
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searchHistory: searchHistory ?? this.searchHistory,
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);
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}
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}) => SearchState._(
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status: status ?? this.status,
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query: query ?? this.query,
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currentTab: currentTab ?? this.currentTab,
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currentSort: currentSort ?? this.currentSort,
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posts: posts ?? this.posts,
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actors: actors ?? this.actors,
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feeds: feeds ?? this.feeds,
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starterPacks: starterPacks ?? this.starterPacks,
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cursor: identical(cursor, _unset) ? this.cursor : cursor as String?,
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starterPacksCursor: identical(starterPacksCursor, _unset) ? this.starterPacksCursor : starterPacksCursor as String?,
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hitsTotal: identical(hitsTotal, _unset) ? this.hitsTotal : hitsTotal as int?,
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errorMessage: identical(errorMessage, _unset) ? this.errorMessage : errorMessage as String?,
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isLoadingMore: isLoadingMore ?? this.isLoadingMore,
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typeaheadActors: typeaheadActors ?? this.typeaheadActors,
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searchHistory: searchHistory ?? this.searchHistory,
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);
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@override
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List<Object?> get props => [
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test/features/feed/cubit/post_action_cubit_test.dart
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test/features/feed/cubit/post_action_cubit_test.dart
···
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isA<PostActionState>()
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.having((s) => s.isLiked, 'isLiked', isFalse)
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.having((s) => s.likeCount, 'likeCount', 4)
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.having((s) => s.likeUri, 'likeUri', isNull)
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.having((s) => s.isLoadingLike, 'isLoadingLike', isFalse),
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],
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);
···
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isA<PostActionState>()
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.having((s) => s.isReposted, 'isReposted', isFalse)
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.having((s) => s.repostCount, 'repostCount', 2)
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.having((s) => s.repostUri, 'repostUri', isNull)
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.having((s) => s.isLoadingRepost, 'isLoadingRepost', isFalse),
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],
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);
···
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expect(copied.isLiked, isTrue);
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expect(copied.likeCount, 1);
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expect(copied.postUri, testPostUri);
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});
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test('copyWith can explicitly clear nullable fields', () {
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const state = PostActionState(
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postUri: testPostUri,
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likeUri: testLikeUri,
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repostUri: testRepostUri,
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error: 'oops',
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);
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final copied = state.copyWith(likeUri: null, repostUri: null, error: null);
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expect(copied.likeUri, isNull);
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expect(copied.repostUri, isNull);
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expect(copied.error, isNull);
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});
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});
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}