Add const/references to all signal parameters

src/analyzer/analyzercontainer.h

@@ -53,7 +53,7 @@ class AnalyzerContainer : public QWidget {
   static const char *kSettingsFramerate;
 
  signals:
-  void WheelEvent(int delta);
+  void WheelEvent(const int delta);
 
  protected:
   void mouseReleaseEvent(QMouseEvent*) override;

src/collection/collection.h

@@ -81,7 +81,7 @@ class SCollection : public QObject {
   void SongsRatingChanged(const SongList &songs, const bool save_tags = false);
 
  signals:
-  void Error(QString);
+  void Error(const QString &error);
   void ExitFinished();
 
  private:

src/collection/collectionbackend.h

@@ -254,23 +254,23 @@ class CollectionBackend : public CollectionBackendInterface {
   void ExpireSongs(const int directory_id, const int expire_unavailable_songs_days);
 
  signals:
-  void DirectoryDiscovered(CollectionDirectory, CollectionSubdirectoryList);
-  void DirectoryDeleted(CollectionDirectory);
+  void DirectoryDiscovered(const CollectionDirectory &dir, const CollectionSubdirectoryList &subdir);
+  void DirectoryDeleted(const CollectionDirectory &dir);
 
-  void SongsDiscovered(SongList);
-  void SongsDeleted(SongList);
-  void SongsStatisticsChanged(SongList, bool = false);
+  void SongsDiscovered(const SongList &songs);
+  void SongsDeleted(const SongList &songs);
+  void SongsStatisticsChanged(const SongList &songs, const bool save_tags = false);
 
   void DatabaseReset();
 
-  void TotalSongCountUpdated(int);
-  void TotalArtistCountUpdated(int);
-  void TotalAlbumCountUpdated(int);
-  void SongsRatingChanged(SongList, bool);
+  void TotalSongCountUpdated(const int count);
+  void TotalArtistCountUpdated(const int count);
+  void TotalAlbumCountUpdated(const int count);
+  void SongsRatingChanged(const SongList &songs, const bool save_tags);
 
   void ExitFinished();
 
-  void Error(QString);
+  void Error(const QString &error);
 
  private:
   struct CompilationInfo {

src/collection/collectionfilterwidget.h

@@ -96,7 +96,7 @@ class CollectionFilterWidget : public QWidget {
   void UpPressed();
   void DownPressed();
   void ReturnPressed();
-  void Filter(QString text);
+  void Filter(const QString &text);
 
  protected:
   void keyReleaseEvent(QKeyEvent *e) override;

src/collection/collectionmodel.h

@@ -199,10 +199,10 @@ class CollectionModel : public SimpleTreeModel<CollectionItem> {
   static QString ContainerKey(const GroupBy group_by, const bool separate_albums_by_grouping, const Song &song);
 
  signals:
-  void TotalSongCountUpdated(int count);
-  void TotalArtistCountUpdated(int count);
-  void TotalAlbumCountUpdated(int count);
-  void GroupingChanged(CollectionModel::Grouping g, bool separate_albums_by_grouping);
+  void TotalSongCountUpdated(const int count);
+  void TotalArtistCountUpdated(const int count);
+  void TotalAlbumCountUpdated(const int count);
+  void GroupingChanged(const CollectionModel::Grouping g, const bool separate_albums_by_grouping);
 
  public slots:
   void SetFilterMode(CollectionFilterOptions::FilterMode filter_mode);

src/collection/collectionview.h

@@ -89,7 +89,7 @@ class CollectionView : public AutoExpandingTreeView {
   void TotalSongCountUpdated_();
   void TotalArtistCountUpdated_();
   void TotalAlbumCountUpdated_();
-  void Error(QString);
+  void Error(const QString &error);
 
  protected:
   // QWidget

src/collection/collectionwatcher.h

@@ -70,18 +70,18 @@ class CollectionWatcher : public QObject {
   void RescanSongsAsync(const SongList &songs);
 
  signals:
-  void NewOrUpdatedSongs(SongList);
-  void SongsMTimeUpdated(SongList);
-  void SongsDeleted(SongList);
-  void SongsUnavailable(SongList songs, bool unavailable = true);
-  void SongsReadded(SongList songs, bool unavailable = false);
-  void SubdirsDiscovered(CollectionSubdirectoryList subdirs);
-  void SubdirsMTimeUpdated(CollectionSubdirectoryList subdirs);
+  void NewOrUpdatedSongs(const SongList &songs);
+  void SongsMTimeUpdated(const SongList &songs);
+  void SongsDeleted(const SongList &songs);
+  void SongsUnavailable(const SongList &songs, const bool unavailable = true);
+  void SongsReadded(const SongList &songs, const bool unavailable = false);
+  void SubdirsDiscovered(const CollectionSubdirectoryList &subdirs);
+  void SubdirsMTimeUpdated(const CollectionSubdirectoryList &subdirs);
   void CompilationsNeedUpdating();
-  void UpdateLastSeen(int directory_id, int expire_unavailable_songs_days);
+  void UpdateLastSeen(const int directory_id, const int expire_unavailable_songs_days);
   void ExitFinished();
 
-  void ScanStarted(int task_id);
+  void ScanStarted(const int task_id);
 
  public slots:
   void AddDirectory(const CollectionDirectory &dir, const CollectionSubdirectoryList &subdirs);

src/collection/groupbydialog.h

@@ -49,7 +49,7 @@ class GroupByDialog : public QDialog {
   void accept() override;
 
  signals:
-  void Accepted(CollectionModel::Grouping g, bool separate_albums_by_grouping);
+  void Accepted(const CollectionModel::Grouping g, const bool separate_albums_by_grouping);
 
  private slots:
   void Reset();

src/core/application.h

@@ -118,9 +118,9 @@ class Application : public QObject {
   void OpenSettingsDialogAtPage(SettingsDialog::Page page);
 
  signals:
-  void ErrorAdded(QString message);
+  void ErrorAdded(const QString &message);
   void SettingsChanged();
-  void SettingsDialogRequested(SettingsDialog::Page page);
+  void SettingsDialogRequested(const SettingsDialog::Page page);
   void ExitFinished();
   void ClearPixmapDiskCache();
 

src/core/database.h

@@ -88,8 +88,8 @@ class Database : public QObject {
 
  signals:
   void ExitFinished();
-  void Error(QString error);
-  void Errors(QStringList errors);
+  void Error(const QString &error);
+  void Errors(const QStringList &errors);
 
  private slots:
   void Exit();

src/core/deletefiles.h

@@ -48,7 +48,7 @@ class DeleteFiles : public QObject {
   void Start(const QStringList &filenames);
 
  signals:
-  void Finished(SongList songs_with_errors);
+  void Finished(const SongList &songs_with_errors);
 
  private slots:
   void ProcessSomeFiles();

src/core/filesystemwatcherinterface.h

@@ -40,7 +40,7 @@ class FileSystemWatcherInterface : public QObject {
   static FileSystemWatcherInterface *Create(QObject *parent = nullptr);
 
  signals:
-  void PathChanged(QString path);
+  void PathChanged(const QString &path);
 };
 
 #endif

src/core/macfslistener.h

@@ -45,7 +45,7 @@ class MacFSListener : public FileSystemWatcherInterface {
   void Clear();
 
  signals:
-  void PathChanged(QString path);
+  void PathChanged(const QString &path);
 
  private slots:
   void UpdateStream();

src/core/macsystemtrayicon.h

@@ -76,7 +76,7 @@ class SystemTrayIcon : public QObject {
   void ActionChanged();
 
  signals:
-  void ChangeVolume(int delta);
+  void ChangeVolume(const int delta);
   void SeekForward();
   void SeekBackward();
   void NextTrack();

src/core/mainwindow.h

@@ -132,12 +132,12 @@ class MainWindow : public QMainWindow, public PlatformInterface {
   bool LoadUrl(const QString &url) override;
 
  signals:
-  void AlbumCoverReady(Song song, QImage image);
+  void AlbumCoverReady(const Song &song, const QImage &image);
   void SearchCoverInProgress();
   // Signals that stop playing after track was toggled.
-  void StopAfterToggled(bool stop);
+  void StopAfterToggled(const bool stop);
 
-  void AuthorizationUrlReceived(QUrl url);
+  void AuthorizationUrlReceived(const QUrl &url);
 
  private slots:
   void FilePathChanged(const QString &path);

src/core/mergedproxymodel.h

@@ -85,7 +85,7 @@ class MergedProxyModel : public QAbstractProxyModel {
   QModelIndexList mapToSource(const QModelIndexList &proxy_indexes) const;
 
  signals:
-  void SubModelReset(QModelIndex root, QAbstractItemModel *model);
+  void SubModelReset(const QModelIndex root, QAbstractItemModel *model);
 
  private slots:
   void SourceModelReset();

src/core/mpris2.h

@@ -188,18 +188,18 @@ class Mpris2 : public QObject {
 
  signals:
   // Player
-  void Seeked(qint64 position);
+  void Seeked(const qint64 position);
 
   // TrackList
-  void TrackListReplaced(Track_Ids Tracks, QDBusObjectPath CurrentTrack);
-  void TrackAdded(TrackMetadata Metadata, QDBusObjectPath AfterTrack);
-  void TrackRemoved(QDBusObjectPath trackId);
-  void TrackMetadataChanged(QDBusObjectPath trackId, TrackMetadata metadata);
+  void TrackListReplaced(const Track_Ids &tracks, const QDBusObjectPath &current_track);
+  void TrackAdded(const TrackMetadata &metadata, const QDBusObjectPath &after_track);
+  void TrackRemoved(const QDBusObjectPath &track_id);
+  void TrackMetadataChanged(const QDBusObjectPath &track_id, const TrackMetadata &metadata);
 
   void RaiseMainWindow();
 
   // Playlist
-  void PlaylistChanged(MprisPlaylist playlist);
+  void PlaylistChanged(const MprisPlaylist &playlist);
 
  private slots:
   void AlbumCoverLoaded(const Song &song, AlbumCoverLoaderResultPtr result = AlbumCoverLoaderResultPtr());

src/core/player.h

@@ -111,20 +111,20 @@ class PlayerInterface : public QObject {
   // Emitted only when playback is manually resumed
   void Resumed();
   void Stopped();
-  void Error(QString message = QString());
+  void Error(const QString &message = QString());
   void PlaylistFinished();
-  void VolumeEnabled(bool);
-  void VolumeChanged(uint volume);
+  void VolumeEnabled(const bool volume_enabled);
+  void VolumeChanged(const uint volume);
   void TrackSkipped(PlaylistItemPtr old_track);
   // Emitted when there's a manual change to the current's track position.
-  void Seeked(qint64 microseconds);
+  void Seeked(const qint64 microseconds);
 
   // Emitted when Player has processed a request to play another song.
   // This contains the URL of the song and a flag saying whether it was able to play the song.
-  void SongChangeRequestProcessed(QUrl url, bool valid);
+  void SongChangeRequestProcessed(const QUrl &url, const bool valid);
 
   // The toggle parameter is true when user requests to toggle visibility for Pretty OSD
-  void ForceShowOSD(Song, bool toggle);
+  void ForceShowOSD(const Song &song, const bool toggle);
 
   void Authenticated();
 
@@ -193,7 +193,7 @@ class Player : public PlayerInterface {
   void HandleAuthentication();
 
  signals:
-  void EngineChanged(Engine::EngineType enginetype);
+  void EngineChanged(const Engine::EngineType enginetype);
 
  private slots:
   void EngineStateChanged(const Engine::State);

src/core/qtsystemtrayicon.h

@@ -69,7 +69,7 @@ class SystemTrayIcon : public QSystemTrayIcon {
   void UpdateIcon();
 
  signals:
-  void ChangeVolume(int delta);
+  void ChangeVolume(const int delta);
   void SeekForward();
   void SeekBackward();
   void NextTrack();

src/core/songloader.h

@@ -89,7 +89,7 @@ class SongLoader : public QObject {
 
  signals:
   void AudioCDTracksLoadFinished();
-  void LoadAudioCDFinished(bool success);
+  void LoadAudioCDFinished(const bool success);
   void LoadRemoteFinished();
 
  private slots:

src/core/urlhandler.h

@@ -91,7 +91,7 @@ class UrlHandler : public QObject {
   virtual LoadResult StartLoading(const QUrl &url) { return LoadResult(url); }
 
  signals:
-  void AsyncLoadComplete(UrlHandler::LoadResult result);
+  void AsyncLoadComplete(const UrlHandler::LoadResult &result);
 
 };
 

src/covermanager/albumcoverchoicecontroller.h

@@ -158,7 +158,7 @@ class AlbumCoverChoiceController : public QWidget {
   void SaveEmbeddedCoverAsyncFinished(quint64 id, const bool success, const bool cleared);
 
  signals:
-  void Error(QString);
+  void Error(const QString &error);
   void AutomaticCoverSearchDone();
 
  private:

src/covermanager/albumcoverexporter.h

@@ -49,7 +49,7 @@ class AlbumCoverExporter : public QObject {
   int request_count() { return static_cast<int>(requests_.size()); }
 
  signals:
-  void AlbumCoversExportUpdate(int exported, int skipped, int all);
+  void AlbumCoversExportUpdate(const int exported, const int skipped, const int all);
 
  private slots:
   void CoverExported();

src/covermanager/albumcoverfetcher.h

@@ -118,12 +118,12 @@ class AlbumCoverFetcher : public QObject {
   void Clear();
 
  signals:
-  void AlbumCoverFetched(quint64 request_id, AlbumCoverImageResultPtr result, CoverSearchStatistics statistics);
-  void SearchFinished(quint64 request_id, CoverProviderSearchResults results, CoverSearchStatistics statistics);
+  void AlbumCoverFetched(const quint64 request_id, AlbumCoverImageResultPtr result, const CoverSearchStatistics &statistics);
+  void SearchFinished(const quint64 request_id, const CoverProviderSearchResults &results, const CoverSearchStatistics &statistics);
 
  private slots:
-  void SingleSearchFinished(const quint64, const CoverProviderSearchResults &results);
-  void SingleCoverFetched(const quint64, AlbumCoverImageResultPtr result);
+  void SingleSearchFinished(const quint64 id, const CoverProviderSearchResults &results);
+  void SingleCoverFetched(const quint64 id, AlbumCoverImageResultPtr result);
   void StartRequests();
 
  private:

src/covermanager/albumcoverfetchersearch.h

@@ -66,10 +66,10 @@ class AlbumCoverFetcherSearch : public QObject {
 
  signals:
   // It's the end of search (when there was no fetch-me-a-cover request).
-  void SearchFinished(quint64, CoverProviderSearchResults results);
+  void SearchFinished(quint64, const CoverProviderSearchResults &results);
 
   // It's the end of search and we've fetched a cover.
-  void AlbumCoverFetched(const quint64, AlbumCoverImageResultPtr result);
+  void AlbumCoverFetched(const quint64 id, AlbumCoverImageResultPtr result);
 
  private slots:
   void ProviderSearchResults(const int id, const CoverProviderSearchResults &results);

src/covermanager/albumcoverloader.h

@@ -79,8 +79,8 @@ class AlbumCoverLoader : public QObject {
 
  signals:
   void ExitFinished();
-  void AlbumCoverLoaded(quint64 id, AlbumCoverLoaderResultPtr result);
-  void SaveEmbeddedCoverAsyncFinished(quint64 id, bool success, bool cleared);
+  void AlbumCoverLoaded(const quint64 id, AlbumCoverLoaderResultPtr result);
+  void SaveEmbeddedCoverAsyncFinished(const quint64 id, const bool success, const bool cleared);
 
  protected slots:
   void Exit();

src/covermanager/albumcovermanager.h

@@ -147,7 +147,7 @@ class AlbumCoverManager : public QMainWindow {
   bool ItemHasCover(const AlbumItem &item) const;
 
  signals:
-  void Error(QString);
+  void Error(const QString &error);
   void AddToPlaylist(QMimeData *data);
 
  private slots:

src/covermanager/coverprovider.h

@@ -68,11 +68,11 @@ class CoverProvider : public QObject {
   virtual void Error(const QString &error, const QVariant &debug = QVariant()) = 0;
 
  signals:
-  void AuthenticationComplete(bool, QStringList = QStringList());
+  void AuthenticationComplete(const bool success, const QStringList &errors = QStringList());
   void AuthenticationSuccess();
-  void AuthenticationFailure(QStringList);
-  void SearchResults(int, CoverProviderSearchResults);
-  void SearchFinished(int, CoverProviderSearchResults);
+  void AuthenticationFailure(const QStringList &errors);
+  void SearchResults(const int id, const CoverProviderSearchResults &results);
+  void SearchFinished(const int id, const CoverProviderSearchResults &results);
 
  protected:
   using Param = QPair<QString, QString>;

src/covermanager/currentalbumcoverloader.h

@@ -52,8 +52,8 @@ class CurrentAlbumCoverLoader : public QObject {
   void LoadAlbumCover(const Song &song);
 
  signals:
-  void AlbumCoverLoaded(Song song, AlbumCoverLoaderResultPtr result);
-  void ThumbnailLoaded(Song song, QUrl thumbnail_uri, const QImage &image);
+  void AlbumCoverLoaded(const Song &song, AlbumCoverLoaderResultPtr result);
+  void ThumbnailLoaded(const Song &song, const QUrl &thumbnail_uri, const QImage &image);
 
  private slots:
   void TempAlbumCoverLoaded(const quint64 id, AlbumCoverLoaderResultPtr result);

src/device/cddadevice.h

@@ -56,7 +56,7 @@ class CddaDevice : public ConnectedDevice {
   static QStringList url_schemes() { return QStringList() << "cdda"; }
 
  signals:
-  void SongsDiscovered(SongList songs);
+  void SongsDiscovered(const SongList &songs);
 
  private slots:
   void SongsLoaded(const SongList &songs);

src/device/cddasongloader.h

@@ -57,10 +57,10 @@ class CddaSongLoader : public QObject {
   QUrl GetUrlFromTrack(const int track_number) const;
 
  signals:
-  void SongsLoadError(QString error);
-  void SongsLoaded(SongList songs);
-  void SongsDurationLoaded(SongList songs, QString error = QString());
-  void SongsMetadataLoaded(SongList songs);
+  void SongsLoadError(const QString &error);
+  void SongsLoaded(const SongList &songs);
+  void SongsDurationLoaded(const SongList &songs, const QString &error = QString());
+  void SongsMetadataLoaded(const SongList &songs);
 
  private slots:
 #ifdef HAVE_MUSICBRAINZ

src/device/connecteddevice.h

@@ -75,10 +75,10 @@ class ConnectedDevice : public QObject, public virtual MusicStorage, public std:
   void BackendCloseFinished();
 
  signals:
-  void TaskStarted(int id);
-  void SongCountUpdated(int count);
-  void DeviceConnectFinished(QString id, bool success);
-  void DeviceCloseFinished(QString id);
+  void TaskStarted(const int id);
+  void SongCountUpdated(const int count);
+  void DeviceConnectFinished(const QString &id, const bool success);
+  void DeviceCloseFinished(const QString &id);
 
  protected:
   void InitBackendDirectory(const QString &mount_point, const bool first_time, const bool rewrite_path = true);

src/device/devicelister.h

@@ -82,10 +82,10 @@ class DeviceLister : public QObject {
   virtual void Exit();
 
  signals:
-  void DeviceAdded(QString id);
-  void DeviceRemoved(QString id);
-  void DeviceChanged(QString id);
-  void DeviceMounted(QString id, int request_id, bool success);
+  void DeviceAdded(const QString &id);
+  void DeviceRemoved(const QString &id);
+  void DeviceChanged(const QString &id);
+  void DeviceMounted(const QString &id, const int request_id, const bool success);
   void ExitFinished();
 
  protected:

src/device/devicemanager.h

@@ -120,8 +120,8 @@ class DeviceManager : public SimpleTreeModel<DeviceInfo> {
 
  signals:
   void ExitFinished();
-  void DeviceConnected(QModelIndex idx);
-  void DeviceDisconnected(QModelIndex idx);
+  void DeviceConnected(const QModelIndex idx);
+  void DeviceDisconnected(const QModelIndex idx);
   void DeviceCreatedFromDB(DeviceInfo *info);
 
  private slots:

src/device/gpodloader.h

@@ -53,9 +53,9 @@ class GPodLoader : public QObject {
   void LoadDatabase();
 
  signals:
-  void Error(QString message);
-  void TaskStarted(int task_id);
-  void LoadFinished(Itdb_iTunesDB *db, bool success);
+  void Error(const QString &message);
+  void TaskStarted(const int task_id);
+  void LoadFinished(Itdb_iTunesDB *db, const bool success);
 
  private:
   Itdb_iTunesDB *TryLoad();

src/device/mtploader.h

@@ -49,9 +49,9 @@ class MtpLoader : public QObject {
   void LoadDatabase();
 
  signals:
-  void Error(QString message);
-  void TaskStarted(int task_id);
-  void LoadFinished(bool success, MtpConnection*);
+  void Error(const QString &message);
+  void TaskStarted(const int task_id);
+  void LoadFinished(const bool success, MtpConnection *connection);
 
  private:
   bool TryLoad();

src/dialogs/edittagdialog.h

@@ -77,7 +77,7 @@ class EditTagDialog : public QDialog {
   void accept() override;
 
  signals:
-  void Error(QString message);
+  void Error(const QString &message);
 
  protected:
   bool eventFilter(QObject *o, QEvent *e) override;

src/dialogs/trackselectiondialog.h

@@ -54,8 +54,8 @@ class TrackSelectionDialog : public QDialog {
   void accept() override;
 
  signals:
-  void Error(QString);
-  void SongChosen(Song original_song, Song new_metadata);
+  void Error(const QString &error);
+  void SongChosen(const Song &original_song, const Song &new_metadata);
 
  private slots:
   void UpdateStack();

src/engine/enginebase.h

@@ -137,23 +137,23 @@ class Base : public QObject {
 
   void FadeoutFinishedSignal();
 
-  void StatusText(QString text);
-  void Error(QString text);
+  void StatusText(const QString &text);
+  void Error(const QString &text);
 
   // Emitted when there was a fatal error
   void FatalError();
   // Emitted when Engine was unable to play a song with the given QUrl.
-  void InvalidSongRequested(QUrl url);
+  void InvalidSongRequested(const QUrl &url);
   // Emitted when Engine successfully started playing a song with the given QUrl.
-  void ValidSongRequested(QUrl url);
+  void ValidSongRequested(const QUrl &url);
 
-  void MetaData(Engine::SimpleMetaBundle);
+  void MetaData(const Engine::SimpleMetaBundle &bundle);
 
   // Signals that the engine's state has changed (a stream was stopped for example).
   // Always use the state from event, because it's not guaranteed that immediate subsequent call to state() won't return a stale value.
-  void StateChanged(Engine::State);
+  void StateChanged(const Engine::State state);
 
-  void VolumeChanged(uint volume);
+  void VolumeChanged(const uint volume);
 
  protected:
 

src/engine/gstenginepipeline.h

@@ -126,16 +126,16 @@ class GstEnginePipeline : public QObject {
   void SetFaderVolume(const qreal volume);
 
  signals:
-  void Error(int pipeline_id, int domain, int error_code, QString message, QString debug);
+  void Error(const int pipeline_id, const int domain, const int error_code, const QString &message, const QString &debug);
 
-  void EndOfStreamReached(int pipeline_id, bool has_next_track);
-  void MetadataFound(int pipeline_id, const Engine::SimpleMetaBundle &bundle);
+  void EndOfStreamReached(const int pipeline_id, const bool has_next_track);
+  void MetadataFound(const int pipeline_id, const Engine::SimpleMetaBundle &bundle);
 
-  void VolumeChanged(uint volume);
+  void VolumeChanged(const uint volume);
   void FaderFinished();
 
   void BufferingStarted();
-  void BufferingProgress(int percent);
+  void BufferingProgress(const int percent);
   void BufferingFinished();
 
  protected:

src/equalizer/equalizer.h

@@ -67,10 +67,10 @@ class Equalizer : public QDialog {
   float stereo_balance() const;
 
  signals:
-  void StereoBalancerEnabledChanged(bool enabled);
-  void StereoBalanceChanged(float balance);
-  void EqualizerEnabledChanged(bool enabled);
-  void EqualizerParametersChanged(int preamp, QList<int> band_gains);
+  void StereoBalancerEnabledChanged(const bool enabled);
+  void StereoBalanceChanged(const float balance);
+  void EqualizerEnabledChanged(const bool enabled);
+  void EqualizerParametersChanged(const int preamp, const QList<int> &band_gains);
 
  protected:
   void closeEvent(QCloseEvent*) override;

src/equalizer/equalizerslider.cpp

@@ -56,7 +56,7 @@ EqualizerSlider::~EqualizerSlider() {
   delete ui_;
 }
 
-void EqualizerSlider::OnValueChanged(int value) {
+void EqualizerSlider::OnValueChanged(const int value) {
 
   // Converting % to dB as per GstEnginePipeline::UpdateEqualizer():
   float gain = (static_cast<int>(value) < 0) ? static_cast<float>(value) * static_cast<float>(0.24) : static_cast<float>(value) * static_cast<float>(0.12);
@@ -70,7 +70,7 @@ int EqualizerSlider::value() const {
   return ui_->slider->value();
 }
 
-void EqualizerSlider::set_value(int value) {
+void EqualizerSlider::set_value(const int value) {
   ui_->slider->setValue(value);
 }
 

src/equalizer/equalizerslider.h

@@ -38,13 +38,13 @@ class EqualizerSlider : public QWidget {
   ~EqualizerSlider() override;
 
   int value() const;
-  void set_value(int value);
+  void set_value(const int value);
 
  signals:
-  void ValueChanged(int value);
+  void ValueChanged(const int value);
 
  public slots:
-  void OnValueChanged(int value);
+  void OnValueChanged(const int value);
 
  private:
   Ui_EqualizerSlider *ui_;

src/globalshortcuts/globalshortcutsbackend.h

@@ -55,7 +55,7 @@ class GlobalShortcutsBackend : public QObject {
   bool is_active() const { return active_; }
 
  signals:
-  void RegisterFinished(bool success);
+  void RegisterFinished(const bool success);
 
  protected:
   virtual bool DoRegister() = 0;

src/internet/internetcollectionview.h

@@ -86,8 +86,8 @@ class InternetCollectionView : public AutoExpandingTreeView {
   void TotalSongCountUpdated_();
   void TotalArtistCountUpdated_();
   void TotalAlbumCountUpdated_();
-  void Error(QString);
-  void RemoveSongs(SongList songs);
+  void Error(const QString &error);
+  void RemoveSongs(const SongList &songs);
 
  protected:
   // QWidget

src/internet/internetsearchview.h

@@ -140,9 +140,9 @@ class InternetSearchView : public QWidget {
 
  signals:
   void AddToPlaylist(QMimeData*);
-  void AddArtistsSignal(SongList);
-  void AddAlbumsSignal(SongList);
-  void AddSongsSignal(SongList);
+  void AddArtistsSignal(const SongList &songs);
+  void AddAlbumsSignal(const SongList &songs);
+  void AddSongsSignal(const SongList &songs);
 
  private slots:
   void SwapModels();

src/internet/internetservice.h

@@ -85,53 +85,52 @@ class InternetService : public QObject {
   void ExitFinished();
   void RequestLogin();
   void RequestLogout();
-  void LoginWithCredentials(QString api_token, QString username, QString password);
-  void LoginWithHostname(QString hostname, int, QString username, QString password);
+  void LoginWithCredentials(const QString &api_token, const QString &username, const QString &password);
   void LoginSuccess();
-  void LoginFailure(QString failure_reason);
-  void LoginComplete(bool success, QString error = QString());
+  void LoginFailure(const QString &failure_reason);
+  void LoginComplete(const bool success, const QString &error = QString());
 
   void TestSuccess();
-  void TestFailure(QString failure_reason);
-  void TestComplete(bool success, QString error = QString());
+  void TestFailure(const QString &failure_reason);
+  void TestComplete(const bool success, const QString &error = QString());
 
-  void Error(QString error);
-  void Results(SongMap songs, QString error);
-  void UpdateStatus(QString text);
-  void ProgressSetMaximum(int max);
-  void UpdateProgress(int max);
+  void Error(const QString &error);
+  void Results(const SongMap &songs, const QString &error);
+  void UpdateStatus(const QString &text);
+  void ProgressSetMaximum(const int max);
+  void UpdateProgress(const int max);
 
-  void ArtistsResults(SongMap songs, QString error);
-  void ArtistsUpdateStatus(QString text);
-  void ArtistsProgressSetMaximum(int max);
-  void ArtistsUpdateProgress(int max);
+  void ArtistsResults(const SongMap &songs, const QString &error);
+  void ArtistsUpdateStatus(const QString &text);
+  void ArtistsProgressSetMaximum(const int max);
+  void ArtistsUpdateProgress(const int max);
 
-  void AlbumsResults(SongMap songs, QString error);
-  void AlbumsUpdateStatus(QString text);
-  void AlbumsProgressSetMaximum(int max);
-  void AlbumsUpdateProgress(int max);
+  void AlbumsResults(const SongMap &songs, const QString &error);
+  void AlbumsUpdateStatus(const QString &text);
+  void AlbumsProgressSetMaximum(const int max);
+  void AlbumsUpdateProgress(const int max);
 
-  void SongsResults(SongMap songs, QString error);
-  void SongsUpdateStatus(QString text);
-  void SongsProgressSetMaximum(int max);
-  void SongsUpdateProgress(int max);
+  void SongsResults(const SongMap &songs, const QString &error);
+  void SongsUpdateStatus(const QString &text);
+  void SongsProgressSetMaximum(const int max);
+  void SongsUpdateProgress(const int max);
 
-  void SearchResults(int id, SongMap songs, QString error);
-  void SearchUpdateStatus(int id, QString text);
-  void SearchProgressSetMaximum(int id, int max);
-  void SearchUpdateProgress(int id, int max);
+  void SearchResults(const int id, const SongMap &songs, const QString &error);
+  void SearchUpdateStatus(const int id, const QString &text);
+  void SearchProgressSetMaximum(const int id, const int max);
+  void SearchUpdateProgress(const int id, const int max);
 
-  void AddArtists(SongList songs);
-  void AddAlbums(SongList songs);
-  void AddSongs(SongList songs);
+  void AddArtists(const SongList &songs);
+  void AddAlbums(const SongList &songs);
+  void AddSongs(const SongList &songs);
 
-  void RemoveArtists(SongList songs);
-  void RemoveAlbums(SongList songs);
-  void RemoveSongsByList(SongList songs);
-  void RemoveSongsByMap(SongMap songs);
+  void RemoveArtists(const SongList &songs);
+  void RemoveAlbums(const SongList &songs);
+  void RemoveSongsByList(const SongList &songs);
+  void RemoveSongsByMap(const SongMap &songs);
 
-  void StreamURLFailure(uint id, QUrl original_url, QString error);
-  void StreamURLSuccess(uint id, QUrl original_url, QUrl stream_url, Song::FileType filetype, int samplerate, int bit_depth, qint64 duration);
+  void StreamURLFailure(const uint id, const QUrl &original_url, const QString &error);
+  void StreamURLSuccess(const uint id, const QUrl &original_url, const QUrl &stream_url, const Song::FileType filetype, const int samplerate, const int bit_depth, const qint64 duration);
 
  protected:
   Application *app_;

src/lyrics/lyricsfetcher.h

@@ -59,8 +59,8 @@ class LyricsFetcher : public QObject {
   void AddRequest(const Request &request);
 
  signals:
-  void LyricsFetched(quint64 request_id, QString provider, QString lyrics);
-  void SearchFinished(quint64 request_id, LyricsSearchResults results);
+  void LyricsFetched(const quint64 request_id, const QString &provider, const QString &lyrics);
+  void SearchFinished(const quint64 request_id, const LyricsSearchResults &results);
 
  private slots:
   void SingleSearchFinished(const quint64 request_id, const LyricsSearchResults &results);

src/lyrics/lyricsfetchersearch.h

@@ -44,8 +44,8 @@ class LyricsFetcherSearch : public QObject {
   void Cancel();
 
  signals:
-  void SearchFinished(quint64, LyricsSearchResults results);
-  void LyricsFetched(quint64, QString provider, QString lyrics);
+  void SearchFinished(const quint64 id, const LyricsSearchResults &results);
+  void LyricsFetched(const quint64 id, const QString &provider, const QString &lyrics);
 
  private slots:
   void ProviderSearchFinished(const int id, const LyricsSearchResults &results);

src/lyrics/lyricsprovider.h

@@ -60,10 +60,10 @@ class LyricsProvider : public QObject {
   QString ParseLyricsFromHTML(const QString &content, const QRegularExpression &start_tag, const QRegularExpression &end_tag, const QRegularExpression &lyrics_start, const bool multiple);
 
  signals:
-  void AuthenticationComplete(bool, QStringList = QStringList());
+  void AuthenticationComplete(const bool success, const QStringList &errors = QStringList());
   void AuthenticationSuccess();
-  void AuthenticationFailure(QStringList);
-  void SearchFinished(int id, LyricsSearchResults results = LyricsSearchResults());
+  void AuthenticationFailure(const QStringList &errors);
+  void SearchFinished(const int id, const LyricsSearchResults &results = LyricsSearchResults());
 
  protected:
   NetworkAccessManager *network_;

src/moodbar/moodbarcontroller.h

@@ -36,7 +36,7 @@ class MoodbarController : public QObject {
   void ReloadSettings();
 
  signals:
-  void CurrentMoodbarDataChanged(QByteArray data);
+  void CurrentMoodbarDataChanged(const QByteArray &data);
 
  private slots:
   void CurrentSongChanged(const Song &song);

src/moodbar/moodbarpipeline.h

@@ -47,7 +47,7 @@ class MoodbarPipeline : public QObject {
   void Start();
 
  signals:
-  void Finished(bool success);
+  void Finished(const bool success);
 
  private:
   GstElement *CreateElement(const QString &factory_name);

src/musicbrainz/acoustidclient.h

@@ -59,7 +59,7 @@ class AcoustidClient : public QObject {
   void CancelAll();
 
  signals:
-  void Finished(int id, QStringList mbid_list, QString error = QString());
+  void Finished(const int id, const QStringList &mbid_list, const QString &error = QString());
 
  private slots:
   void RequestFinished(QNetworkReply *reply, const int id);

src/musicbrainz/musicbrainzclient.h

@@ -101,9 +101,9 @@ class MusicBrainzClient : public QObject {
 
  signals:
   // Finished signal emitted when fechting songs tags
-  void Finished(int id, MusicBrainzClient::ResultList result, QString error = QString());
+  void Finished(const int id, const MusicBrainzClient::ResultList &result, const QString &error = QString());
   // Finished signal emitted when fechting album's songs tags using DiscId
-  void DiscIdFinished(QString artist, QString album, MusicBrainzClient::ResultList result, QString error = QString());
+  void DiscIdFinished(const QString &artist, const QString &album, const MusicBrainzClient::ResultList &result, const QString &error = QString());
 
  private slots:
   void FlushRequests();

src/musicbrainz/tagfetcher.h

@@ -48,8 +48,8 @@ class TagFetcher : public QObject {
   void Cancel();
 
  signals:
-  void Progress(Song original_song, QString stage);
-  void ResultAvailable(Song original_song, SongList songs_guessed, QString error = QString());
+  void Progress(const Song &original_song, const QString &stage);
+  void ResultAvailable(const Song &original_song, const SongList &songs_guessed, const QString &error = QString());
 
  private slots:
   void FingerprintFound(const int index);

src/organize/organize.h

@@ -74,9 +74,9 @@ class Organize : public QObject {
   void Start();
 
  signals:
-  void Finished(QStringList files_with_errors, QStringList);
-  void FileCopied(int database_id);
-  void SongPathChanged(Song song, QFileInfo new_file, std::optional<int> new_collection_directory_id);
+  void Finished(const QStringList &files_with_errors, const QStringList&);
+  void FileCopied(const int database_id);
+  void SongPathChanged(const Song &song, const QFileInfo &new_file, const std::optional<int> new_collection_directory_id);
 
  protected:
   void timerEvent(QTimerEvent *e) override;

src/organize/organizedialog.h

@@ -87,7 +87,7 @@ class OrganizeDialog : public QDialog {
   void SetLoadingSongs(const bool loading);
 
  signals:
-  void FileCopied(int);
+  void FileCopied(const int);
 
  public slots:
   void accept() override;

src/playlist/playlist.h

@@ -325,11 +325,11 @@ class Playlist : public QAbstractListModel {
  signals:
   void RestoreFinished();
   void PlaylistLoaded();
-  void CurrentSongChanged(Song metadata);
-  void SongMetadataChanged(Song metadata);
-  void EditingFinished(const int playlist_id, QModelIndex idx);
-  void PlayRequested(QModelIndex idx, Playlist::AutoScroll autoscroll);
-  void MaybeAutoscroll(Playlist::AutoScroll autoscroll);
+  void CurrentSongChanged(const Song &metadata);
+  void SongMetadataChanged(const Song &metadata);
+  void EditingFinished(const int playlist_id, const QModelIndex idx);
+  void PlayRequested(const QModelIndex idx, const Playlist::AutoScroll autoscroll);
+  void MaybeAutoscroll(const Playlist::AutoScroll autoscroll);
 
   // Signals that the underlying list of items was changed, meaning that something was added to it, removed from it or the ordering changed.
   void PlaylistChanged();

src/playlist/playlistcontainer.h

@@ -65,8 +65,8 @@ class PlaylistContainer : public QWidget {
   bool eventFilter(QObject *objectWatched, QEvent *event) override;
 
  signals:
-  void TabChanged(int id);
-  void Rename(int id, QString new_name);
+  void TabChanged(const int id);
+  void Rename(const int id, const QString &new_name);
 
   void UndoRedoActionsChanged(QAction *undo, QAction *redo);
   void ViewSelectionModelChanged();

src/playlist/playlistheader.h

@@ -53,9 +53,9 @@ class PlaylistHeader : public StretchHeaderView {
 #endif
 
  signals:
-  void SectionVisibilityChanged(int logical, bool visible);
+  void SectionVisibilityChanged(const int logical, const bool visible);
   void MouseEntered();
-  void SectionRatingLockStatusChanged(bool);
+  void SectionRatingLockStatusChanged(const bool);
 
  private slots:
   void HideCurrent();

src/playlist/playlistlistmodel.h

@@ -81,8 +81,8 @@ class PlaylistListModel : public QStandardItemModel {
   bool setData(const QModelIndex &idx, const QVariant &value, int role) override;
 
  signals:
-  void PlaylistPathChanged(int id, QString new_path);
-  void PlaylistRenamed(int id, QString new_name);
+  void PlaylistPathChanged(const int id, const QString &new_path);
+  void PlaylistRenamed(const int id, const QString &new_name);
 
  private slots:
   void RowsChanged(const QModelIndex &begin, const QModelIndex &end);

src/playlist/playlistlistview.h

@@ -41,7 +41,7 @@ class PlaylistListView : public AutoExpandingTreeView {
   bool ItemsSelected() const;
 
  signals:
-  void ItemsSelectedChanged(bool);
+  void ItemsSelectedChanged(const bool);
 
  protected:
   // QWidget

src/playlist/playlistmanager.h

@@ -117,25 +117,25 @@ class PlaylistManagerInterface : public QObject {
   void PlaylistManagerInitialized();
   void AllPlaylistsLoaded();
 
-  void PlaylistAdded(int id, QString name, bool favorite);
-  void PlaylistDeleted(int id);
-  void PlaylistClosed(int id);
-  void PlaylistRenamed(int id, QString new_name);
-  void PlaylistFavorited(int id, bool favorite);
-  void CurrentChanged(Playlist *new_playlist, int scroll_position = 0);
+  void PlaylistAdded(const int id, const QString &name, const bool favorite);
+  void PlaylistDeleted(const int id);
+  void PlaylistClosed(const int id);
+  void PlaylistRenamed(const int id, const QString &new_name);
+  void PlaylistFavorited(const int id, const bool favorite);
+  void CurrentChanged(Playlist *new_playlist, const int scroll_position = 0);
   void ActiveChanged(Playlist *new_playlist);
 
-  void Error(QString message);
-  void SummaryTextChanged(QString summary);
+  void Error(const QString &message);
+  void SummaryTextChanged(const QString &summary);
 
   // Forwarded from individual playlists
-  void CurrentSongChanged(Song song);
-  void SongMetadataChanged(Song song);
+  void CurrentSongChanged(const Song &song);
+  void SongMetadataChanged(const Song &song);
 
   // Signals that one of manager's playlists has changed (new items, new ordering etc.) - the argument shows which.
   void PlaylistChanged(Playlist *playlist);
-  void EditingFinished(int playlist_id, QModelIndex idx);
-  void PlayRequested(QModelIndex idx, Playlist::AutoScroll autoscroll);
+  void EditingFinished(const int playlist_id, const QModelIndex idx);
+  void PlayRequested(const QModelIndex idx, const Playlist::AutoScroll autoscroll);
 };
 
 class PlaylistManager : public PlaylistManagerInterface {

src/playlist/playlistsequence.h

@@ -77,8 +77,8 @@ class PlaylistSequence : public QWidget {
   void CycleRepeatMode();
 
  signals:
-  void RepeatModeChanged(PlaylistSequence::RepeatMode mode);
-  void ShuffleModeChanged(PlaylistSequence::ShuffleMode mode);
+  void RepeatModeChanged(const PlaylistSequence::RepeatMode mode);
+  void ShuffleModeChanged(const PlaylistSequence::ShuffleMode mode);
 
  private slots:
   void RepeatActionTriggered(QAction *action);

src/playlist/playlisttabbar.h

@@ -72,12 +72,12 @@ class PlaylistTabBar : public QTabBar {
   void InsertTab(const int id, const int index, const QString &text, const bool favorite);
 
  signals:
-  void CurrentIdChanged(int id);
-  void Rename(int id, QString name);
-  void Close(int id);
-  void Save(int id);
-  void PlaylistOrderChanged(QList<int> ids);
-  void PlaylistFavorited(int id, bool favorite);
+  void CurrentIdChanged(const int id);
+  void Rename(const int id, const QString &name);
+  void Close(const int id);
+  void Save(const int id);
+  void PlaylistOrderChanged(const QList<int> &ids);
+  void PlaylistFavorited(const int id, const bool favorite);
 
  protected:
   void contextMenuEvent(QContextMenuEvent *e) override;

src/playlist/playlistview.h

@@ -127,14 +127,14 @@ class PlaylistView : public QTreeView {
   void edit(const QModelIndex &idx) { QAbstractItemView::edit(idx); }
 
  signals:
-  void PlayItem(QModelIndex idx, Playlist::AutoScroll autoscroll);
-  void PlayPause(const quint64 offset_nanosec = 0, Playlist::AutoScroll autoscroll = Playlist::AutoScroll::Never);
-  void RightClicked(QPoint global_pos, QModelIndex idx);
+  void PlayItem(const QModelIndex idx, const Playlist::AutoScroll autoscroll);
+  void PlayPause(const quint64 offset_nanosec = 0, const Playlist::AutoScroll autoscroll = Playlist::AutoScroll::Never);
+  void RightClicked(const QPoint global_pos, const QModelIndex idx);
   void SeekForward();
   void SeekBackward();
   void FocusOnFilterSignal(QKeyEvent *event);
   void BackgroundPropertyChanged();
-  void ColumnAlignmentChanged(ColumnAlignmentMap alignment);
+  void ColumnAlignmentChanged(const ColumnAlignmentMap alignment);
 
  protected:
   // QWidget

src/playlist/songloaderinserter.h

@@ -48,9 +48,9 @@ class SongLoaderInserter : public QObject {
   void LoadAudioCD(Playlist *destination, int row, bool play_now, bool enqueue, bool enqueue_next);
 
  signals:
-  void Error(QString message);
+  void Error(const QString &message);
   void PreloadFinished();
-  void EffectiveLoadFinished(SongList songs);
+  void EffectiveLoadFinished(const SongList &songs);
 
  private slots:
   void DestinationDestroyed();

src/qobuz/qobuzfavoriterequest.h

@@ -49,12 +49,12 @@ class QobuzFavoriteRequest : public QobuzBaseRequest {
   };
 
  signals:
-  void ArtistsAdded(SongList);
-  void AlbumsAdded(SongList);
-  void SongsAdded(SongList);
-  void ArtistsRemoved(SongList);
-  void AlbumsRemoved(SongList);
-  void SongsRemoved(SongList);
+  void ArtistsAdded(const SongList &songs);
+  void AlbumsAdded(const SongList &songs);
+  void SongsAdded(const SongList &songs);
+  void ArtistsRemoved(const SongList &songs);
+  void AlbumsRemoved(const SongList &songs);
+  void SongsRemoved(const SongList &songs);
 
  private slots:
   void AddFavoritesReply(QNetworkReply *reply, const QobuzFavoriteRequest::FavoriteType type, const SongList &songs);

src/qobuz/qobuzrequest.h

@@ -99,11 +99,11 @@ class QobuzRequest : public QobuzBaseRequest {
 
  signals:
   void LoginSuccess();
-  void LoginFailure(QString failure_reason);
-  void Results(int id, SongMap songs, QString error);
-  void UpdateStatus(int id, QString text);
-  void UpdateProgress(int id, int max);
-  void StreamURLFinished(QUrl original_url, QUrl url, Song::FileType, QString error = QString());
+  void LoginFailure(const QString &failure_reason);
+  void Results(const int id, const SongMap &songs, const QString &error);
+  void UpdateStatus(const int id, const QString &text);
+  void UpdateProgress(const int id, const int max);
+  void StreamURLFinished(const QUrl &original_url, const QUrl &url, const Song::FileType filetype, const QString &error = QString());
 
  private slots:
   void ArtistsReplyReceived(QNetworkReply *reply, const int limit_requested, const int offset_requested);

src/qobuz/qobuzstreamurlrequest.h

@@ -54,8 +54,8 @@ class QobuzStreamURLRequest : public QobuzBaseRequest {
 
  signals:
   void TryLogin();
-  void StreamURLFailure(uint id, QUrl original_url, QString error);
-  void StreamURLSuccess(uint id, QUrl original_url, QUrl stream_url, Song::FileType filetype, int samplerate, int bit_depth, qint64 duration);
+  void StreamURLFailure(const uint id, const QUrl &original_url, const QString &error);
+  void StreamURLSuccess(const uint id, const QUrl &original_url, const QUrl &stream_url, const Song::FileType filetype, const int samplerate, const int bit_depth, const qint64 duration);
 
  private slots:
   void StreamURLReceived();

src/queue/queue.h

@@ -83,9 +83,9 @@ class Queue : public QAbstractProxyModel {
   void UpdateSummaryText();
 
  signals:
-  void TotalLengthChanged(quint64 length);
-  void ItemCountChanged(int count);
-  void SummaryTextChanged(QString message);
+  void TotalLengthChanged(const quint64 length);
+  void ItemCountChanged(const int count);
+  void SummaryTextChanged(const QString &message);
 
  private slots:
   void SourceDataChanged(const QModelIndex &top_left, const QModelIndex &bottom_right);

src/radios/radiobackend.h

@@ -46,7 +46,7 @@ class RadioBackend : public QObject {
   void DeleteChannels();
 
  signals:
-  void NewChannels(RadioChannelList);
+  void NewChannels(const RadioChannelList &channels);
   void ExitFinished();
 
  private slots:

src/radios/radioservice.h

@@ -52,7 +52,7 @@ class RadioService : public QObject {
   virtual QUrl Donate() = 0;
 
  signals:
-  void NewChannels(RadioChannelList channels = RadioChannelList());
+  void NewChannels(const RadioChannelList &channels = RadioChannelList());
 
  public slots:
   virtual void GetChannels() = 0;

src/scrobbler/audioscrobbler.h

@@ -71,11 +71,11 @@ class AudioScrobbler : public QObject {
   void ErrorReceived(const QString &error);
 
  signals:
-  void ErrorMessage(QString);
-  void ScrobblingEnabledChanged(bool value);
-  void ScrobblingOfflineChanged(bool value);
-  void ScrobbleButtonVisibilityChanged(bool value);
-  void LoveButtonVisibilityChanged(bool value);
+  void ErrorMessage(const QString &error);
+  void ScrobblingEnabledChanged(const bool value);
+  void ScrobblingOfflineChanged(const bool value);
+  void ScrobbleButtonVisibilityChanged(const bool value);
+  void LoveButtonVisibilityChanged(const bool value);
 
  private:
   Application *app_;

src/scrobbler/lastfmimport.h

@@ -79,12 +79,12 @@ class LastFMImport : public QObject {
   void FinishCheck();
 
  signals:
-  void UpdatePlayCount(QString, QString, int, bool = false);
-  void UpdateLastPlayed(QString, QString, QString, qint64);
-  void UpdateTotal(int, int);
-  void UpdateProgress(int, int);
+  void UpdatePlayCount(const QString&, const QString&, const int, const bool = false);
+  void UpdateLastPlayed(const QString&, const QString&, const QString&, const qint64);
+  void UpdateTotal(const int, const int);
+  void UpdateProgress(const int, const int);
   void Finished();
-  void FinishedWithError(QString);
+  void FinishedWithError(const QString&);
 
  private slots:
   void FlushRequests();

src/scrobbler/listenbrainzscrobbler.h

@@ -72,7 +72,7 @@ class ListenBrainzScrobbler : public ScrobblerService {
   void Love() override;
 
  signals:
-  void AuthenticationComplete(bool success, QString error = QString());
+  void AuthenticationComplete(const bool success, const QString &error = QString());
 
  public slots:
   void WriteCache() override { cache_->WriteCache(); }

src/scrobbler/scrobblerservice.h

@@ -72,7 +72,7 @@ class ScrobblerService : public QObject {
   virtual void WriteCache() = 0;
 
  signals:
-  void ErrorMessage(QString);
+  void ErrorMessage(const QString &error);
 
  private:
   QString name_;

src/scrobbler/scrobblingapi20.h

@@ -70,7 +70,7 @@ class ScrobblingAPI20 : public ScrobblerService {
   void Love() override;
 
  signals:
-  void AuthenticationComplete(bool success, QString error = QString());
+  void AuthenticationComplete(const bool success, const QString &error = QString());
 
  public slots:
   void WriteCache() override { cache_->WriteCache(); }

src/settings/qobuzsettingspage.h

@@ -45,7 +45,7 @@ class QobuzSettingsPage : public SettingsPage {
   bool eventFilter(QObject *object, QEvent *event) override;
 
  signals:
-  void Login(QString username, QString password, QString token);
+  void Login(const QString &username, const QString &password, const QString &token);
 
  private slots:
   void LoginClicked();

src/settings/settingsdialog.h

@@ -139,7 +139,7 @@ class SettingsDialog : public QDialog {
 
  signals:
   void ReloadSettings();
-  void NotificationPreview(OSDBase::Behaviour, QString, QString);
+  void NotificationPreview(const OSDBase::Behaviour, const QString&, const QString&);
 
  private slots:
   void CurrentItemChanged(QTreeWidgetItem *item);

src/settings/settingspage.h

@@ -76,7 +76,7 @@ class SettingsPage : public QWidget {
   virtual void Cancel() {}
 
  signals:
-  void NotificationPreview(OSDBase::Behaviour, QString, QString);
+  void NotificationPreview(const OSDBase::Behaviour, const QString&, const QString&);
 
  private:
   SettingsDialog *dialog_;

src/settings/subsonicsettingspage.h

@@ -53,7 +53,7 @@ class SubsonicSettingsPage : public SettingsPage {
   bool eventFilter(QObject *object, QEvent *event) override;
 
  signals:
-  void Test(QUrl url, QString username, QString password, SubsonicSettingsPage::AuthMethod auth_method, bool redirect = false);
+  void Test(const QUrl &url, const QString &username, const QString &password, const SubsonicSettingsPage::AuthMethod auth_method, const bool redirect = false);
 
  private slots:
   void TestClicked();

src/settings/tidalsettingspage.h

@@ -53,8 +53,8 @@ class TidalSettingsPage : public SettingsPage {
   bool eventFilter(QObject *object, QEvent *event) override;
 
  signals:
-  void Authorize(QString client_id);
-  void Login(QString api_token, QString username, QString password);
+  void Authorize(const QString &client_id);
+  void Login(const QString &api_token, const QString &username, const QString &password);
 
  private slots:
   void OAuthClicked(const bool enabled);

src/smartplaylists/playlistgenerator.h

@@ -85,7 +85,7 @@ class PlaylistGenerator : public QObject, public std::enable_shared_from_this<Pl
   virtual int GetDynamicFuture() { return kDefaultDynamicFuture; }
 
  signals:
-  void Error(QString message);
+  void Error(const QString &message);
 
  protected:
   CollectionBackend *backend_;

src/smartplaylists/playlistgeneratorinserter.h

@@ -47,8 +47,8 @@ class PlaylistGeneratorInserter : public QObject {
   static PlaylistItemPtrList Generate(PlaylistGeneratorPtr generator, const int dynamic_count);
 
  signals:
-  void Error(QString message);
-  void PlayRequested(QModelIndex idx, Playlist::AutoScroll autoscroll);
+  void Error(const QString &message);
+  void PlayRequested(const QModelIndex idx, const Playlist::AutoScroll autoscroll);
 
  private slots:
   void Finished();

src/smartplaylists/smartplaylistsview.h

@@ -40,7 +40,7 @@ class SmartPlaylistsView : public QListView {
 
  signals:
   void ItemsSelectedChanged();
-  void RightClicked(QPoint global_pos, QModelIndex idx);
+  void RightClicked(const QPoint global_pos, const QModelIndex idx);
 
 };
 

src/subsonic/subsonicrequest.h

@@ -78,10 +78,10 @@ class SubsonicRequest : public SubsonicBaseRequest {
   };
 
  signals:
-  void Results(SongMap songs, QString error);
-  void UpdateStatus(QString text);
-  void ProgressSetMaximum(int max);
-  void UpdateProgress(int max);
+  void Results(const SongMap &songs, const QString &error);
+  void UpdateStatus(const QString &text);
+  void ProgressSetMaximum(const int max);
+  void UpdateProgress(const int progress);
 
  private slots:
   void AlbumsReplyReceived(QNetworkReply *reply, const int offset_requested, const int size_requested);

src/tidal/tidalfavoriterequest.h

@@ -52,12 +52,12 @@ class TidalFavoriteRequest : public TidalBaseRequest {
   };
 
  signals:
-  void ArtistsAdded(SongList);
-  void AlbumsAdded(SongList);
-  void SongsAdded(SongList);
-  void ArtistsRemoved(SongList);
-  void AlbumsRemoved(SongList);
-  void SongsRemoved(SongList);
+  void ArtistsAdded(const SongList &songs);
+  void AlbumsAdded(const SongList &songs);
+  void SongsAdded(const SongList &songs);
+  void ArtistsRemoved(const SongList &songs);
+  void AlbumsRemoved(const SongList &songs);
+  void SongsRemoved(const SongList &songs);
 
  private slots:
   void AddFavoritesReply(QNetworkReply *reply, const TidalFavoriteRequest::FavoriteType type, const SongList &songs);

src/tidal/tidalrequest.h

@@ -99,11 +99,11 @@ class TidalRequest : public TidalBaseRequest {
 
  signals:
   void LoginSuccess();
-  void LoginFailure(QString failure_reason);
-  void Results(int id, SongMap songs = SongMap(), QString error = QString());
-  void UpdateStatus(int id, QString text);
-  void UpdateProgress(int id, int max);
-  void StreamURLFinished(QUrl original_url, QUrl url, Song::FileType, QString error = QString());
+  void LoginFailure(const QString &failure_reason);
+  void Results(const int id, const SongMap &songs = SongMap(), const QString &error = QString());
+  void UpdateStatus(const int id, const QString &text);
+  void UpdateProgress(const int id, const int max);
+  void StreamURLFinished(const QUrl &original_url, const QUrl &url, const Song::FileType filetype, const QString &error = QString());
 
  private slots:
   void ArtistsReplyReceived(QNetworkReply *reply, const int limit_requested, const int offset_requested);

src/tidal/tidalstreamurlrequest.h

@@ -58,8 +58,8 @@ class TidalStreamURLRequest : public TidalBaseRequest {
 
  signals:
   void TryLogin();
-  void StreamURLFailure(uint id, QUrl original_url, QString error);
-  void StreamURLSuccess(uint id, QUrl original_url, QUrl stream_url, Song::FileType filetype, int samplerate = -1, int bit_depth = -1, qint64 duration = -1);
+  void StreamURLFailure(const uint id, const QUrl &original_url, const QString &error);
+  void StreamURLSuccess(const uint id, const QUrl &original_url, const QUrl &stream_url, const Song::FileType filetype, const int samplerate = -1, const int bit_depth = -1, const qint64 duration = -1);
 
  private slots:
   void StreamURLReceived();

src/transcoder/transcoder.h

@@ -75,8 +75,8 @@ class Transcoder : public QObject {
   void Cancel();
 
  signals:
-  void JobComplete(QString input, QString output, bool success);
-  void LogLine(QString message);
+  void JobComplete(const QString &input, const QString &output, const bool success);
+  void LogLine(const QString &message);
   void AllJobsComplete();
 
  protected:

src/widgets/fancytabwidget.h

@@ -78,8 +78,8 @@ class FancyTabWidget : public QTabWidget {
   int iconsize_largesidebar() const { return iconsize_largesidebar_; }
 
  signals:
-  void ModeChanged(FancyTabWidget::Mode mode);
-  void CurrentChanged(int);
+  void ModeChanged(const FancyTabWidget::Mode mode);
+  void CurrentChanged(const int);
 
  public slots:
   void setCurrentIndex(int idx);

src/widgets/favoritewidget.h

@@ -44,7 +44,7 @@ class FavoriteWidget : public QWidget {
   QSize sizeHint() const override;
 
  signals:
-  void FavoriteStateChanged(int, bool);
+  void FavoriteStateChanged(const int, const bool);
 
  protected:
   void paintEvent(QPaintEvent *e) override;

src/widgets/fileview.h

@@ -64,13 +64,13 @@ class FileView : public QWidget {
   void keyPressEvent(QKeyEvent *e) override;
 
  signals:
-  void PathChanged(QString path);
+  void PathChanged(const QString &path);
 
   void AddToPlaylist(QMimeData *data);
-  void CopyToCollection(QList<QUrl> urls);
-  void MoveToCollection(QList<QUrl> urls);
-  void CopyToDevice(QList<QUrl> urls);
-  void EditTags(QList<QUrl> urls);
+  void CopyToCollection(const QList<QUrl> &urls);
+  void MoveToCollection(const QList<QUrl> &urls);
+  void CopyToDevice(const QList<QUrl> &urls);
+  void EditTags(const QList<QUrl> &urls);
 
  private slots:
   void FileUp();

src/widgets/fileviewlist.h

@@ -47,11 +47,11 @@ class FileViewList : public QListView {
 
  signals:
   void AddToPlaylist(QMimeData *data);
-  void CopyToCollection(QList<QUrl> urls);
-  void MoveToCollection(QList<QUrl> urls);
-  void CopyToDevice(QList<QUrl> urls);
-  void Delete(QStringList filenames);
-  void EditTags(QList<QUrl> urls);
+  void CopyToCollection(const QList<QUrl> &urls);
+  void MoveToCollection(const QList<QUrl> &urls);
+  void CopyToDevice(const QList<QUrl> &urls);
+  void Delete(const QStringList &filenames);
+  void EditTags(const QList<QUrl> &urls);
   void Back();
   void Forward();
 

src/widgets/multiloadingindicator.h

@@ -46,7 +46,7 @@ class MultiLoadingIndicator : public QWidget {
   QSize sizeHint() const override;
 
  signals:
-  void TaskCountChange(int tasks);
+  void TaskCountChange(const int tasks);
 
  protected:
   void paintEvent(QPaintEvent*) override;

src/widgets/playingwidget.h

@@ -68,7 +68,7 @@ class PlayingWidget : public QWidget {
   bool show_above_status_bar() const { return above_statusbar_action_->isChecked(); }
 
  signals:
-  void ShowAboveStatusBarChanged(bool above);
+  void ShowAboveStatusBarChanged(const bool above);
 
  public slots:
   void Playing();

src/widgets/qsearchfield.h

@@ -36,7 +36,7 @@ class QSearchField : public QWidget {
   void setFocus();
 
  signals:
-  void textChanged(QString text);
+  void textChanged(const QString &text);
   void editingFinished();
   void returnPressed();
 

src/widgets/ratingwidget.h

@@ -55,7 +55,7 @@ class RatingWidget : public QWidget {
   void set_rating(const float rating);
 
  signals:
-  void RatingChanged(float);
+  void RatingChanged(const float rating);
 
  protected:
   void paintEvent(QPaintEvent*) override;

src/widgets/sliderslider.h

@@ -42,7 +42,7 @@ class SliderSlider : public QSlider {
 
  signals:
   // We emit this when the user has specifically changed the slider so connect to it if valueChanged() is too generic Qt also emits valueChanged(int)
-  void SliderReleased(int);
+  void SliderReleased(const int);
 
  protected:
   virtual void slideEvent(QMouseEvent*);