Pass non-trivial/large function args by reference

Fixes a bunch of `-Wclazy-function-args-by-ref` warnings. See
https://github.com/KDE/clazy/blob/master/docs/checks/README-function-args-by-ref.md
for details.

Most of these changes are automated, using the clazy fixit by setting
the `CLAZY_EXPORT_FIXES` before compilation and then running:

    $ mkdir /tmp/patch
    $ find ../src -iname "*.yaml" -exec mv {} /tmp/patch \;
    $ clang-apply-replacements /tmp/patch

44 files changed, 261 insertions, 257 deletions

diff --git a/src/engine/cachingreader/cachingreader.cpp b/src/engine/cachingreader/cachingreader.cpp
index d7332eb27c..592371a686 100644
--- a/src/engine/cachingreader/cachingreader.cpp
+++ b/src/engine/cachingreader/cachingreader.cpp
@@ -40,7 +40,7 @@ const SINT kNumberOfCachedChunksInMemory = 80;
 
 } // anonymous namespace
 
-CachingReader::CachingReader(QString group,
+CachingReader::CachingReader(const QString& group,
         UserSettingsPointer config)
         : m_pConfig(config),
           // Limit the number of in-flight requests to the worker. This should
diff --git a/src/engine/cachingreader/cachingreader.h b/src/engine/cachingreader/cachingreader.h
index 24b039f11e..01529342ea 100644
--- a/src/engine/cachingreader/cachingreader.h
+++ b/src/engine/cachingreader/cachingreader.h
@@ -75,8 +75,8 @@ class CachingReader : public QObject {
 
   public:
     // Construct a CachingReader with the given group.
-    CachingReader(QString group,
-                  UserSettingsPointer _config);
+    CachingReader(const QString& group,
+            UserSettingsPointer _config);
     ~CachingReader() override;
 
     void process();
@@ -115,7 +115,7 @@ class CachingReader : public QObject {
     // Emitted once a new track is loaded and ready to be read from.
     void trackLoading();
     void trackLoaded(TrackPointer pTrack, int iSampleRate, int iNumSamples);
-    void trackLoadFailed(TrackPointer pTrack, QString reason);
+    void trackLoadFailed(TrackPointer pTrack, const QString& reason);
 
   private:
     const UserSettingsPointer m_pConfig;
diff --git a/src/engine/cachingreader/cachingreaderworker.cpp b/src/engine/cachingreader/cachingreaderworker.cpp
index ae5b9d8256..aefd482d04 100644
--- a/src/engine/cachingreader/cachingreaderworker.cpp
+++ b/src/engine/cachingreader/cachingreaderworker.cpp
@@ -18,7 +18,7 @@ mixxx::Logger kLogger("CachingReaderWorker");
 } // anonymous namespace
 
 CachingReaderWorker::CachingReaderWorker(
-        QString group,
+        const QString& group,
         FIFO<CachingReaderChunkReadRequest>* pChunkReadRequestFIFO,
         FIFO<ReaderStatusUpdate>* pReaderStatusFIFO)
         : m_group(group),
diff --git a/src/engine/cachingreader/cachingreaderworker.h b/src/engine/cachingreader/cachingreaderworker.h
index eb0f68081c..6118c58c94 100644
--- a/src/engine/cachingreader/cachingreaderworker.h
+++ b/src/engine/cachingreader/cachingreaderworker.h
@@ -97,7 +97,7 @@ class CachingReaderWorker : public EngineWorker {
 
   public:
     // Construct a CachingReader with the given group.
-    CachingReaderWorker(QString group,
+    CachingReaderWorker(const QString& group,
             FIFO<CachingReaderChunkReadRequest>* pChunkReadRequestFIFO,
             FIFO<ReaderStatusUpdate>* pReaderStatusFIFO);
     ~CachingReaderWorker() override = default;
@@ -115,7 +115,7 @@ class CachingReaderWorker : public EngineWorker {
     // Emitted once a new track is loaded and ready to be read from.
     void trackLoading();
     void trackLoaded(TrackPointer pTrack, int iSampleRate, int iNumSamples);
-    void trackLoadFailed(TrackPointer pTrack, QString reason);
+    void trackLoadFailed(TrackPointer pTrack, const QString& reason);
 
   private:
     const QString m_group;
diff --git a/src/engine/channels/engineaux.cpp b/src/engine/channels/engineaux.cpp
index eaaef154ae..9f75ec6d68 100644
--- a/src/engine/channels/engineaux.cpp
+++ b/src/engine/channels/engineaux.cpp
@@ -46,7 +46,7 @@ bool EngineAux::isActive() {
     return m_wasActive;
 }
 
-void EngineAux::onInputConfigured(AudioInput input) {
+void EngineAux::onInputConfigured(const AudioInput& input) {
     if (input.getType() != AudioPath::AUXILIARY) {
         // This is an error!
         qDebug() << "WARNING: EngineAux connected to AudioInput for a non-auxiliary type!";
@@ -56,7 +56,7 @@ void EngineAux::onInputConfigured(AudioInput input) {
     m_pInputConfigured->forceSet(1.0);
 }
 
-void EngineAux::onInputUnconfigured(AudioInput input) {
+void EngineAux::onInputUnconfigured(const AudioInput& input) {
     if (input.getType() != AudioPath::AUXILIARY) {
         // This is an error!
         qDebug() << "WARNING: EngineAux connected to AudioInput for a non-auxiliary type!";
@@ -66,8 +66,8 @@ void EngineAux::onInputUnconfigured(AudioInput input) {
     m_pInputConfigured->forceSet(0.0);
 }
 
-void EngineAux::receiveBuffer(AudioInput input, const CSAMPLE* pBuffer,
-                              unsigned int nFrames) {
+void EngineAux::receiveBuffer(
+        const AudioInput& input, const CSAMPLE* pBuffer, unsigned int nFrames) {
     Q_UNUSED(input);
     Q_UNUSED(nFrames);
     m_sampleBuffer = pBuffer;
diff --git a/src/engine/channels/engineaux.h b/src/engine/channels/engineaux.h
index cf01a5aad3..d12f65ad8b 100644
--- a/src/engine/channels/engineaux.h
+++ b/src/engine/channels/engineaux.h
@@ -35,16 +35,17 @@ class EngineAux : public EngineChannel, public AudioDestination {
     // the soundcard this AudioDestination was registered for! Beware, in the
     // case of multiple soundcards, this method is not re-entrant but it may be
     // concurrent with EngineMaster processing.
-    virtual void receiveBuffer(AudioInput input, const CSAMPLE* pBuffer,
-                               unsigned int nFrames);
+    virtual void receiveBuffer(const AudioInput& input,
+            const CSAMPLE* pBuffer,
+            unsigned int nFrames);
 
     // Called by SoundManager whenever the aux input is connected to a
     // soundcard input.
-    virtual void onInputConfigured(AudioInput input);
+    virtual void onInputConfigured(const AudioInput& input);
 
     // Called by SoundManager whenever the aux input is disconnected from
     // a soundcard input.
-    virtual void onInputUnconfigured(AudioInput input);
+    virtual void onInputUnconfigured(const AudioInput& input);
 
   private:
     QScopedPointer<ControlObject> m_pInputConfigured;
diff --git a/src/engine/channels/enginedeck.cpp b/src/engine/channels/enginedeck.cpp
index 27431078c6..8eeb3d1bad 100644
--- a/src/engine/channels/enginedeck.cpp
+++ b/src/engine/channels/enginedeck.cpp
@@ -131,7 +131,8 @@ bool EngineDeck::isActive() {
     return active;
 }
 
-void EngineDeck::receiveBuffer(AudioInput input, const CSAMPLE* pBuffer, unsigned int nFrames) {
+void EngineDeck::receiveBuffer(
+        const AudioInput& input, const CSAMPLE* pBuffer, unsigned int nFrames) {
     Q_UNUSED(input);
     Q_UNUSED(nFrames);
     // Skip receiving audio input if passthrough is not active
@@ -143,7 +144,7 @@ void EngineDeck::receiveBuffer(AudioInput input, const CSAMPLE* pBuffer, unsigne
     }
 }
 
-void EngineDeck::onInputConfigured(AudioInput input) {
+void EngineDeck::onInputConfigured(const AudioInput& input) {
     if (input.getType() != AudioPath::VINYLCONTROL) {
         // This is an error!
         qDebug() << "WARNING: EngineDeck connected to AudioInput for a non-vinylcontrol type!";
@@ -153,7 +154,7 @@ void EngineDeck::onInputConfigured(AudioInput input) {
     m_sampleBuffer =  NULL;
 }
 
-void EngineDeck::onInputUnconfigured(AudioInput input) {
+void EngineDeck::onInputUnconfigured(const AudioInput& input) {
     if (input.getType() != AudioPath::VINYLCONTROL) {
         // This is an error!
         qDebug() << "WARNING: EngineDeck connected to AudioInput for a non-vinylcontrol type!";
diff --git a/src/engine/channels/enginedeck.h b/src/engine/channels/enginedeck.h
index f571dadb38..cc0006c9c7 100644
--- a/src/engine/channels/enginedeck.h
+++ b/src/engine/channels/enginedeck.h
@@ -62,16 +62,17 @@ class EngineDeck : public EngineChannel, public AudioDestination {
     // the soundcard this AudioDestination was registered for! Beware, in the
     // case of multiple soundcards, this method is not re-entrant but it may be
     // concurrent with EngineMaster processing.
-    virtual void receiveBuffer(AudioInput input, const CSAMPLE* pBuffer,
-                               unsigned int nFrames);
+    virtual void receiveBuffer(const AudioInput& input,
+            const CSAMPLE* pBuffer,
+            unsigned int nFrames);
 
     // Called by SoundManager whenever the passthrough input is connected to a
     // soundcard input.
-    virtual void onInputConfigured(AudioInput input);
+    virtual void onInputConfigured(const AudioInput& input);
 
     // Called by SoundManager whenever the passthrough input is disconnected
     // from a soundcard input.
-    virtual void onInputUnconfigured(AudioInput input);
+    virtual void onInputUnconfigured(const AudioInput& input);
 
     // Return whether or not passthrough is active
     bool isPassthroughActive() const;
diff --git a/src/engine/channels/enginemicrophone.cpp b/src/engine/channels/enginemicrophone.cpp
index be6e8c4174..ceefe6f5b1 100644
--- a/src/engine/channels/enginemicrophone.cpp
+++ b/src/engine/channels/enginemicrophone.cpp
@@ -43,7 +43,7 @@ bool EngineMicrophone::isActive() {
     return m_wasActive;
 }
 
-void EngineMicrophone::onInputConfigured(AudioInput input) {
+void EngineMicrophone::onInputConfigured(const AudioInput& input) {
     if (input.getType() != AudioPath::MICROPHONE) {
         // This is an error!
         qWarning() << "EngineMicrophone connected to AudioInput for a non-Microphone type!";
@@ -53,7 +53,7 @@ void EngineMicrophone::onInputConfigured(AudioInput input) {
     m_pInputConfigured->forceSet(1.0);
 }
 
-void EngineMicrophone::onInputUnconfigured(AudioInput input) {
+void EngineMicrophone::onInputUnconfigured(const AudioInput& input) {
     if (input.getType() != AudioPath::MICROPHONE) {
         // This is an error!
         qWarning() << "EngineMicrophone connected to AudioInput for a non-Microphone type!";
@@ -63,8 +63,8 @@ void EngineMicrophone::onInputUnconfigured(AudioInput input) {
     m_pInputConfigured->forceSet(0.0);
 }
 
-void EngineMicrophone::receiveBuffer(AudioInput input, const CSAMPLE* pBuffer,
-                                     unsigned int nFrames) {
+void EngineMicrophone::receiveBuffer(
+        const AudioInput& input, const CSAMPLE* pBuffer, unsigned int nFrames) {
     Q_UNUSED(input);
     Q_UNUSED(nFrames);
     m_sampleBuffer = pBuffer;
diff --git a/src/engine/channels/enginemicrophone.h b/src/engine/channels/enginemicrophone.h
index f3ac6f0b3e..0cca9c294c 100644
--- a/src/engine/channels/enginemicrophone.h
+++ b/src/engine/channels/enginemicrophone.h
@@ -38,16 +38,17 @@ class EngineMicrophone : public EngineChannel, public AudioDestination {
     // the soundcard this AudioDestination was registered for! Beware, in the
     // case of multiple soundcards, this method is not re-entrant but it may be
     // concurrent with EngineMaster processing.
-    virtual void receiveBuffer(AudioInput input, const CSAMPLE* pBuffer,
-                               unsigned int iNumSamples);
+    virtual void receiveBuffer(const AudioInput& input,
+            const CSAMPLE* pBuffer,
+            unsigned int iNumSamples);
 
     // Called by SoundManager whenever the microphone input is connected to a
     // soundcard input.
-    virtual void onInputConfigured(AudioInput input);
+    virtual void onInputConfigured(const AudioInput& input);
 
     // Called by SoundManager whenever the microphone input is disconnected from
     // a soundcard input.
-    virtual void onInputUnconfigured(AudioInput input);
+    virtual void onInputUnconfigured(const AudioInput& input);
 
     bool isSolo();
     double getSoloDamping();
diff --git a/src/engine/controls/bpmcontrol.cpp b/src/engine/controls/bpmcontrol.cpp
index 20285ca89f..52370da16d 100644
--- a/src/engine/controls/bpmcontrol.cpp
+++ b/src/engine/controls/bpmcontrol.cpp
@@ -40,7 +40,7 @@ constexpr int kLocalBpmSpan = 4;
 constexpr SINT kSamplesPerFrame = 2;
 }
 
-BpmControl::BpmControl(QString group,
+BpmControl::BpmControl(const QString& group,
         UserSettingsPointer pConfig)
         : EngineControl(group, pConfig),
           m_tapFilter(this, kBpmTapFilterLength, kBpmTapMaxInterval),
diff --git a/src/engine/controls/bpmcontrol.h b/src/engine/controls/bpmcontrol.h
index c23716dd1a..fc753a2e80 100644
--- a/src/engine/controls/bpmcontrol.h
+++ b/src/engine/controls/bpmcontrol.h
@@ -23,7 +23,7 @@ class BpmControl : public EngineControl {
     Q_OBJECT
 
   public:
-    BpmControl(QString group, UserSettingsPointer pConfig);
+    BpmControl(const QString& group, UserSettingsPointer pConfig);
     ~BpmControl() override;
 
     double getBpm() const;
diff --git a/src/engine/controls/clockcontrol.cpp b/src/engine/controls/clockcontrol.cpp
index 2a374aa1b4..f48660bb4c 100644
--- a/src/engine/controls/clockcontrol.cpp
+++ b/src/engine/controls/clockcontrol.cpp
@@ -6,7 +6,7 @@
 #include "preferences/usersettings.h"
 #include "track/track.h"
 
-ClockControl::ClockControl(QString group, UserSettingsPointer pConfig)
+ClockControl::ClockControl(const QString& group, UserSettingsPointer pConfig)
         : EngineControl(group, pConfig) {
     m_pCOBeatActive = new ControlObject(ConfigKey(group, "beat_active"));
     m_pCOBeatActive->set(0.0);
diff --git a/src/engine/controls/clockcontrol.h b/src/engine/controls/clockcontrol.h
index 719a13bd5d..5076a5cd9b 100644
--- a/src/engine/controls/clockcontrol.h
+++ b/src/engine/controls/clockcontrol.h
@@ -12,8 +12,8 @@ class ControlObject;
 class ClockControl: public EngineControl {
     Q_OBJECT
   public:
-    ClockControl(QString group,
-                 UserSettingsPointer pConfig);
+    ClockControl(const QString& group,
+            UserSettingsPointer pConfig);
 
     ~ClockControl() override;
 
diff --git a/src/engine/controls/cuecontrol.cpp b/src/engine/controls/cuecontrol.cpp
index ab53d49e46..22a1ef74f9 100644
--- a/src/engine/controls/cuecontrol.cpp
+++ b/src/engine/controls/cuecontrol.cpp
@@ -46,7 +46,7 @@ inline mixxx::RgbColor::optional_t doubleToRgbColor(double value) {
 
 } // namespace
 
-CueControl::CueControl(QString group,
+CueControl::CueControl(const QString& group,
         UserSettingsPointer pConfig)
         : EngineControl(group, pConfig),
           m_pConfig(pConfig),
@@ -316,7 +316,7 @@ void CueControl::createControls() {
     }
 }
 
-void CueControl::attachCue(CuePointer pCue, HotcueControl* pControl) {
+void CueControl::attachCue(const CuePointer& pCue, HotcueControl* pControl) {
     VERIFY_OR_DEBUG_ASSERT(pControl) {
         return;
     }
@@ -1825,7 +1825,7 @@ ConfigKey HotcueControl::keyForControl(int hotcue, const char* name) {
     return key;
 }
 
-HotcueControl::HotcueControl(QString group, int i)
+HotcueControl::HotcueControl(const QString& group, int i)
         : m_group(group),
           m_iHotcueNumber(i),
           m_pCue(NULL),
@@ -1960,7 +1960,7 @@ double HotcueControl::getPosition() const {
     return m_hotcuePosition->get();
 }
 
-void HotcueControl::setCue(CuePointer pCue) {
+void HotcueControl::setCue(const CuePointer& pCue) {
     setPosition(pCue->getPosition());
     setColor(pCue->getColor());
     // set pCue only if all other data is in place
diff --git a/src/engine/controls/cuecontrol.h b/src/engine/controls/cuecontrol.h
index ee17926cf3..e954b82cda 100644
--- a/src/engine/controls/cuecontrol.h
+++ b/src/engine/controls/cuecontrol.h
@@ -43,13 +43,13 @@ inline SeekOnLoadMode seekOnLoadModeFromDouble(double value) {
 class HotcueControl : public QObject {
     Q_OBJECT
   public:
-    HotcueControl(QString group, int hotcueNumber);
+    HotcueControl(const QString& group, int hotcueNumber);
     ~HotcueControl() override;
 
     inline int getHotcueNumber() { return m_iHotcueNumber; }
     inline CuePointer getCue() { return m_pCue; }
     double getPosition() const;
-    void setCue(CuePointer pCue);
+    void setCue(const CuePointer& pCue);
     void resetCue();
     void setPosition(double position);
     void setColor(mixxx::RgbColor::optional_t newColor);
@@ -120,8 +120,8 @@ class HotcueControl : public QObject {
 class CueControl : public EngineControl {
     Q_OBJECT
   public:
-    CueControl(QString group,
-               UserSettingsPointer pConfig);
+    CueControl(const QString& group,
+            UserSettingsPointer pConfig);
     ~CueControl() override;
 
     void hintReader(HintVector* pHintList) override;
@@ -188,7 +188,7 @@ class CueControl : public EngineControl {
 
     // These methods are not thread safe, only call them when the lock is held.
     void createControls();
-    void attachCue(CuePointer pCue, HotcueControl* pControl);
+    void attachCue(const CuePointer& pCue, HotcueControl* pControl);
     void detachCue(HotcueControl* pControl);
     void loadCuesFromTrack();
     double quantizeCuePoint(double position);
diff --git a/src/engine/controls/enginecontrol.cpp b/src/engine/controls/enginecontrol.cpp
index a5d0a0555f..22eaa2ab01 100644
--- a/src/engine/controls/enginecontrol.cpp
+++ b/src/engine/controls/enginecontrol.cpp
@@ -7,8 +7,8 @@
 #include "engine/sync/enginesync.h"
 #include "mixer/playermanager.h"
 
-EngineControl::EngineControl(QString group,
-                             UserSettingsPointer pConfig)
+EngineControl::EngineControl(const QString& group,
+        UserSettingsPointer pConfig)
         : m_group(group),
           m_pConfig(pConfig),
           m_pEngineMaster(nullptr),
diff --git a/src/engine/controls/enginecontrol.h b/src/engine/controls/enginecontrol.h
index d8c4de38b1..e4e00f8b35 100644
--- a/src/engine/controls/enginecontrol.h
+++ b/src/engine/controls/enginecontrol.h
@@ -38,8 +38,8 @@ const int kNoTrigger = -1;
 class EngineControl : public QObject {
     Q_OBJECT
   public:
-    EngineControl(QString group,
-                  UserSettingsPointer pConfig);
+    EngineControl(const QString& group,
+            UserSettingsPointer pConfig);
     ~EngineControl() override;
 
     // Called by EngineBuffer::process every latency period. See the above
diff --git a/src/engine/controls/keycontrol.cpp b/src/engine/controls/keycontrol.cpp
index cc32cbcfac..8fac74c1fd 100644
--- a/src/engine/controls/keycontrol.cpp
+++ b/src/engine/controls/keycontrol.cpp
@@ -14,8 +14,8 @@
 static const double kLockCurrentKey = 1;
 static const double kKeepUnlockedKey = 1;
 
-KeyControl::KeyControl(QString group,
-                       UserSettingsPointer pConfig)
+KeyControl::KeyControl(const QString& group,
+        UserSettingsPointer pConfig)
         : EngineControl(group, pConfig) {
     m_pitchRateInfo.pitchRatio = 1.0;
     m_pitchRateInfo.tempoRatio = 1.0;
diff --git a/src/engine/controls/keycontrol.h b/src/engine/controls/keycontrol.h
index 622ae59f96..7835ce3033 100644
--- a/src/engine/controls/keycontrol.h
+++ b/src/engine/controls/keycontrol.h
@@ -26,7 +26,7 @@ class KeyControl : public EngineControl {
         bool keylock;
     };
 
-    KeyControl(QString group, UserSettingsPointer pConfig);
+    KeyControl(const QString& group, UserSettingsPointer pConfig);
     ~KeyControl() override;
 
     // Returns a struct, with the results of the last pitch and tempo calculations
diff --git a/src/engine/controls/loopingcontrol.cpp b/src/engine/controls/loopingcontrol.cpp
index 0f3619d0e3..6888b821b3 100644
--- a/src/engine/controls/loopingcontrol.cpp
+++ b/src/engine/controls/loopingcontrol.cpp
@@ -21,7 +21,7 @@ double LoopingControl::s_dBeatSizes[] = { 0.03125, 0.0625, 0.125, 0.25, 0.5,
 
 // Used to generate the beatloop_%SIZE, beatjump_%SIZE, and loop_move_%SIZE CO
 // ConfigKeys.
-ConfigKey keyForControl(QString group, QString ctrlName, double num) {
+ConfigKey keyForControl(const QString& group, const QString& ctrlName, double num) {
     ConfigKey key;
     key.group = group;
     key.item = ctrlName.arg(num);
@@ -37,8 +37,8 @@ QList<double> LoopingControl::getBeatSizes() {
     return result;
 }
 
-LoopingControl::LoopingControl(QString group,
-                               UserSettingsPointer pConfig)
+LoopingControl::LoopingControl(const QString& group,
+        UserSettingsPointer pConfig)
         : EngineControl(group, pConfig),
           m_bLoopingEnabled(false),
           m_bLoopRollActive(false),
@@ -1305,7 +1305,7 @@ double LoopingControl::seekInsideAdjustedLoop(
     }
 }
 
-BeatJumpControl::BeatJumpControl(QString group, double size)
+BeatJumpControl::BeatJumpControl(const QString& group, double size)
         : m_dBeatJumpSize(size) {
     m_pJumpForward = new ControlPushButton(
             keyForControl(group, "beatjump_%1_forward", size));
@@ -1336,7 +1336,7 @@ void BeatJumpControl::slotJumpForward(double pressed) {
     }
 }
 
-LoopMoveControl::LoopMoveControl(QString group, double size)
+LoopMoveControl::LoopMoveControl(const QString& group, double size)
         : m_dLoopMoveSize(size) {
     m_pMoveForward = new ControlPushButton(
             keyForControl(group, "loop_move_%1_forward", size));
@@ -1367,7 +1367,7 @@ void LoopMoveControl::slotMoveForward(double v) {
     }
 }
 
-BeatLoopingControl::BeatLoopingControl(QString group, double size)
+BeatLoopingControl::BeatLoopingControl(const QString& group, double size)
         : m_dBeatLoopSize(size),
           m_bActive(false) {
     // This is the original beatloop control which is now deprecated. Its value
diff --git a/src/engine/controls/loopingcontrol.h b/src/engine/controls/loopingcontrol.h
index 3faaea34ea..45b20bc052 100644
--- a/src/engine/controls/loopingcontrol.h
+++ b/src/engine/controls/loopingcontrol.h
@@ -29,7 +29,7 @@ class LoopingControl : public EngineControl {
   public:
     static QList<double> getBeatSizes();
 
-    LoopingControl(QString group, UserSettingsPointer pConfig);
+    LoopingControl(const QString& group, UserSettingsPointer pConfig);
     ~LoopingControl() override;
 
     // process() updates the internal state of the LoopingControl to reflect the
@@ -179,7 +179,7 @@ class LoopingControl : public EngineControl {
 class LoopMoveControl : public QObject {
     Q_OBJECT
   public:
-    LoopMoveControl(QString group, double size);
+    LoopMoveControl(const QString& group, double size);
     virtual ~LoopMoveControl();
 
   signals:
@@ -200,7 +200,7 @@ class LoopMoveControl : public QObject {
 class BeatJumpControl : public QObject {
     Q_OBJECT
   public:
-    BeatJumpControl(QString group, double size);
+    BeatJumpControl(const QString& group, double size);
     virtual ~BeatJumpControl();
 
   signals:
@@ -221,7 +221,7 @@ class BeatJumpControl : public QObject {
 class BeatLoopingControl : public QObject {
     Q_OBJECT
   public:
-    BeatLoopingControl(QString group, double size);
+    BeatLoopingControl(const QString& gro