Merge branch '2.3' of github.com:mixxxdj/mixxx into cleanup-headers

45 files changed, 653 insertions, 415 deletions

diff --git a/src/controllers/bulk/bulkcontroller.cpp b/src/controllers/bulk/bulkcontroller.cpp
index b81b61defa..5000e9c626 100644
--- a/src/controllers/bulk/bulkcontroller.cpp
+++ b/src/controllers/bulk/bulkcontroller.cpp
@@ -80,7 +80,7 @@ BulkController::BulkController(UserSettingsPointer pConfig,
 
     setDeviceCategory(tr("USB Controller"));
 
-    setDeviceName(QString("%1 %2").arg(product).arg(m_sUID));
+    setDeviceName(QString("%1 %2").arg(product, m_sUID));
 
     setInputDevice(true);
     setOutputDevice(true);
@@ -227,7 +227,7 @@ void BulkController::send(QList<int> data, unsigned int length) {
     send(temp);
 }
 
-void BulkController::send(QByteArray data) {
+void BulkController::send(const QByteArray& data) {
     int ret;
     int transferred;
 
diff --git a/src/controllers/bulk/bulkcontroller.h b/src/controllers/bulk/bulkcontroller.h
index 3ee2073628..a8d8f242c9 100644
--- a/src/controllers/bulk/bulkcontroller.h
+++ b/src/controllers/bulk/bulkcontroller.h
@@ -21,7 +21,7 @@ class BulkReader : public QThread {
     void stop();
 
   signals:
-    void incomingData(QByteArray data, mixxx::Duration timestamp);
+    void incomingData(const QByteArray& data, mixxx::Duration timestamp);
 
   protected:
     void run();
@@ -74,7 +74,7 @@ class BulkController : public Controller {
   private:
     // For devices which only support a single report, reportID must be set to
     // 0x0.
-    void send(QByteArray data) override;
+    void send(const QByteArray& data) override;
 
     // Returns a pointer to the currently loaded controller preset. For internal
     // use only.
diff --git a/src/controllers/colormapper.h b/src/controllers/colormapper.h
index 05e2cb9055..10157ed257 100644
--- a/src/controllers/colormapper.h
+++ b/src/controllers/colormapper.h
@@ -13,7 +13,7 @@
 class ColorMapper final {
   public:
     ColorMapper() = delete;
-    explicit ColorMapper(QMap<QRgb, QVariant> availableColors)
+    explicit ColorMapper(const QMap<QRgb, QVariant>& availableColors)
             : m_availableColors(availableColors) {
         DEBUG_ASSERT(!m_availableColors.isEmpty());
     }
diff --git a/src/controllers/colormapperjsproxy.cpp b/src/controllers/colormapperjsproxy.cpp
index c8d7cf1590..3272bd0494 100644
--- a/src/controllers/colormapperjsproxy.cpp
+++ b/src/controllers/colormapperjsproxy.cpp
@@ -2,7 +2,8 @@
 
 #include "controllers/colormapperjsproxy.h"
 
-ColorMapperJSProxy::ColorMapperJSProxy(QScriptEngine* pScriptEngine, QMap<QRgb, QVariant> availableColors)
+ColorMapperJSProxy::ColorMapperJSProxy(QScriptEngine* pScriptEngine,
+        const QMap<QRgb, QVariant>& availableColors)
         : m_pScriptEngine(pScriptEngine),
           m_colorMapper(new ColorMapper(availableColors)) {
 }
diff --git a/src/controllers/colormapperjsproxy.h b/src/controllers/colormapperjsproxy.h
index 3a08f062d5..898b5cb033 100644
--- a/src/controllers/colormapperjsproxy.h
+++ b/src/controllers/colormapperjsproxy.h
@@ -12,7 +12,7 @@ class ColorMapperJSProxy final : public QObject {
     Q_OBJECT
   public:
     ColorMapperJSProxy() = delete;
-    ColorMapperJSProxy(QScriptEngine* pScriptEngine, QMap<QRgb, QVariant> availableColors);
+    ColorMapperJSProxy(QScriptEngine* pScriptEngine, const QMap<QRgb, QVariant>& availableColors);
 
     ~ColorMapperJSProxy() override {
         delete m_colorMapper;
diff --git a/src/controllers/controller.cpp b/src/controllers/controller.cpp
index 43b0a58291..f5eb46d6a4 100644
--- a/src/controllers/controller.cpp
+++ b/src/controllers/controller.cpp
@@ -78,7 +78,7 @@ void Controller::stopLearning() {
 
 }
 
-void Controller::send(QList<int> data, unsigned int length) {
+void Controller::send(const QList<int>& data, unsigned int length) {
     // If you change this implementation, also change it in HidController (That
     // function is required due to HID devices having report IDs)
 
@@ -100,8 +100,7 @@ void Controller::triggerActivity()
         m_userActivityInhibitTimer.start();
     }
 }
-void Controller::receive(const QByteArray data, mixxx::Duration timestamp) {
-
+void Controller::receive(const QByteArray& data, mixxx::Duration timestamp) {
     if (m_pEngine == NULL) {
         //qWarning() << "Controller::receive called with no active engine!";
         // Don't complain, since this will always show after closing a device as
@@ -114,7 +113,9 @@ void Controller::receive(const QByteArray data, mixxx::Duration timestamp) {
     if (ControllerDebug::enabled()) {
         // Formatted packet display
         QString message = QString("%1: t:%2, %3 bytes:\n")
-                .arg(m_sDeviceName).arg(timestamp.formatMillisWithUnit()).arg(length);
+                                  .arg(m_sDeviceName,
+                                          timestamp.formatMillisWithUnit(),
+                                          QString::number(length));
         for(int i=0; i<length; i++) {
             QString spacer=" ";
             if ((i+1) % 4 == 0) spacer="  ";
diff --git a/src/controllers/controller.h b/src/controllers/controller.h
index 24c3f28975..92f75b1e42 100644
--- a/src/controllers/controller.h
+++ b/src/controllers/controller.h
@@ -74,7 +74,7 @@ class Controller : public QObject, ConstControllerPresetVisitor {
     // Handles packets of raw bytes and passes them to an ".incomingData" script
     // function that is assumed to exist. (Sub-classes may want to reimplement
     // this if they have an alternate way of handling such data.)
-    virtual void receive(const QByteArray data, mixxx::Duration timestamp);
+    virtual void receive(const QByteArray& data, mixxx::Duration timestamp);
 
     /// Apply the preset to the controller.
     /// Initializes both controller engine and static output mappings.
@@ -91,7 +91,7 @@ class Controller : public QObject, ConstControllerPresetVisitor {
   protected:
     // The length parameter is here for backwards compatibility for when scripts
     // were required to specify it.
-    Q_INVOKABLE void send(QList<int> data, unsigned int length = 0);
+    Q_INVOKABLE void send(const QList<int>& data, unsigned int length = 0);
 
     // To be called in sub-class' open() functions after opening the device but
     // before starting any input polling/processing.
@@ -107,10 +107,10 @@ class Controller : public QObject, ConstControllerPresetVisitor {
     inline ControllerEngine* getEngine() const {
         return m_pEngine;
     }
-    inline void setDeviceName(QString deviceName) {
+    inline void setDeviceName(const QString& deviceName) {
         m_sDeviceName = deviceName;
     }
-    inline void setDeviceCategory(QString deviceCategory) {
+    inline void setDeviceCategory(const QString& deviceCategory) {
         m_sDeviceCategory = deviceCategory;
     }
     inline void setOutputDevice(bool outputDevice) {
@@ -141,7 +141,7 @@ class Controller : public QObject, ConstControllerPresetVisitor {
   private:
     // This must be reimplemented by sub-classes desiring to send raw bytes to a
     // controller.
-    virtual void send(QByteArray data) = 0;
+    virtual void send(const QByteArray& data) = 0;
 
     // Returns a pointer to the currently loaded controller preset. For internal
     // use only.
diff --git a/src/controllers/controllerdebug.h b/src/controllers/controllerdebug.h
index f3fc5837cf..c8bc556531 100644
--- a/src/controllers/controllerdebug.h
+++ b/src/controllers/controllerdebug.h
@@ -8,7 +8,8 @@ class ControllerDebug {
   public:
     // Any debug statement starting with this prefix bypasses the --logLevel
     // command line flags.
-    static constexpr const char* kLogMessagePrefix = "CDBG";
+    static constexpr const char kLogMessagePrefix[] = "CDBG";
+    static constexpr int kLogMessagePrefixLength = sizeof(kLogMessagePrefix) - 1;
 
     static bool enabled();
 
diff --git a/src/controllers/controllerengine.cpp b/src/controllers/controllerengine.cpp
index c7f1b44c3c..7002f3cb85 100644
--- a/src/controllers/controllerengine.cpp
+++ b/src/controllers/controllerengine.cpp
@@ -84,8 +84,9 @@ Purpose: Calls the same method on a list of JS Objects
 Input:   -
 Output:  -
 -------- ------------------------------------------------------ */
-void ControllerEngine::callFunctionOnObjects(QList<QString> scriptFunctionPrefixes,
-                                             const QString& function, QScriptValueList args) {
+void ControllerEngine::callFunctionOnObjects(const QList<QString>& scriptFunctionPrefixes,
+        const QString& function,
+        const QScriptValueList& args) {
     VERIFY_OR_DEBUG_ASSERT(m_pEngine) {
         return;
     }
@@ -283,8 +284,10 @@ bool ControllerEngine::loadScriptFiles(const QList<ControllerPreset::ScriptFileI
 
     m_lastScriptFiles = scripts;
 
-    connect(&m_scriptWatcher, SIGNAL(fileChanged(QString)),
-            this, SLOT(scriptHasChanged(QString)));
+    connect(&m_scriptWatcher,
+            &QFileSystemWatcher::fileChanged,
+            this,
+            &ControllerEngine::scriptHasChanged);
 
     bool success = result && m_scriptErrors.isEmpty();
     if (!success) {
@@ -301,8 +304,10 @@ void ControllerEngine::scriptHasChanged(const QString& scriptFilename) {
     qDebug() << "ControllerEngine: Reloading Scripts";
     ControllerPresetPointer pPreset = m_pController->getPreset();
 
-    disconnect(&m_scriptWatcher, SIGNAL(fileChanged(QString)),
-               this, SLOT(scriptHasChanged(QString)));
+    disconnect(&m_scriptWatcher,
+            &QFileSystemWatcher::fileChanged,
+            this,
+            &ControllerEngine::scriptHasChanged);
 
     gracefulShutdown();
     uninitializeScriptEngine();
@@ -417,7 +422,7 @@ Input:   'this' object if applicable, Code string
 Output:  false if an exception
 -------- ------------------------------------------------------ */
 bool ControllerEngine::internalExecute(
-        QScriptValue thisObject, const QString& scriptCode) {
+        const QScriptValue& thisObject, const QString& scriptCode) {
     // A special version of safeExecute since we're evaluating strings, not actual functions
     //  (execute() would print an error that it's not a function every time a timer fires.)
     if (m_pEngine == nullptr) {
@@ -448,9 +453,9 @@ Purpose: Evaluate & run script code
 Input:   'this' object if applicable, Code string
 Output:  false if an exception
 -------- ------------------------------------------------------ */
-bool ControllerEngine::internalExecute(QScriptValue thisObject,
+bool ControllerEngine::internalExecute(const QScriptValue& thisObject,
         QScriptValue functionObject,
-        QScriptValueList args) {
+        const QScriptValueList& args) {
     if (m_pEngine == nullptr) {
         qDebug() << "ControllerEngine::execute: No script engine exists!";
         return false;
@@ -485,7 +490,7 @@ bool ControllerEngine::internalExecute(QScriptValue thisObject,
     return !checkException();
 }
 
-bool ControllerEngine::execute(QScriptValue functionObject,
+bool ControllerEngine::execute(const QScriptValue& functionObject,
         unsigned char channel,
         unsigned char control,
         unsigned char value,
@@ -505,8 +510,8 @@ bool ControllerEngine::execute(QScriptValue functionObject,
     return internalExecute(m_pEngine->globalObject(), functionObject, args);
 }
 
-bool ControllerEngine::execute(QScriptValue function,
-        const QByteArray data,
+bool ControllerEngine::execute(const QScriptValue& function,
+        const QByteArray& data,
         mixxx::Duration timestamp) {
     Q_UNUSED(timestamp);
     if (m_pEngine == nullptr) {
@@ -627,8 +632,10 @@ void ControllerEngine::scriptErrorDialog(
 
     if (ErrorDialogHandler::instance()->requestErrorDialog(props)) {
         // Enable custom handling of the dialog buttons
-        connect(ErrorDialogHandler::instance(), SIGNAL(stdButtonClicked(QString, QMessageBox::StandardButton)),
-                this, SLOT(errorDialogButton(QString, QMessageBox::StandardButton)));
+        connect(ErrorDialogHandler::instance(),
+                &ErrorDialogHandler::stdButtonClicked,
+                this,
+                &ControllerEngine::errorDialogButton);
     }
 }
 
@@ -642,9 +649,9 @@ void ControllerEngine::errorDialogButton(const QString& key, QMessageBox::Standa
 
     // Something was clicked, so disable this signal now
     disconnect(ErrorDialogHandler::instance(),
-               SIGNAL(stdButtonClicked(QString, QMessageBox::StandardButton)),
-               this,
-               SLOT(errorDialogButton(QString, QMessageBox::StandardButton)));
+            &ErrorDialogHandler::stdButtonClicked,
+            this,
+            &ControllerEngine::errorDialogButton);
 
     if (button == QMessageBox::Retry) {
         emit resetController();
@@ -680,7 +687,7 @@ ControlObjectScript* ControllerEngine::getControlObjectScript(const QString& gro
    Input:   Control group (e.g. [Channel1]), Key name (e.g. [filterHigh])
    Output:  The value
    -------- ------------------------------------------------------ */
-double ControllerEngine::getValue(QString group, QString name) {
+double ControllerEngine::getValue(const QString& group, const QString& name) {
     ControlObjectScript* coScript = getControlObjectScript(group, name);
     if (coScript == nullptr) {
         qWarning() << "ControllerEngine: Unknown control" << group << name << ", returning 0.0";
@@ -694,7 +701,7 @@ double ControllerEngine::getValue(QString group, QString name) {
    Input:   Control group, Key name, new value
    Output:  -
    -------- ------------------------------------------------------ */
-void ControllerEngine::setValue(QString group, QString name, double newValue) {
+void ControllerEngine::setValue(const QString& group, const QString& name, double newValue) {
     if (isnan(newValue)) {
         qWarning() << "ControllerEngine: script setting [" << group << "," << name
                  << "] to NotANumber, ignoring.";
@@ -717,7 +724,7 @@ void ControllerEngine::setValue(QString group, QString name, double newValue) {
    Input:   Control group (e.g. [Channel1]), Key name (e.g. [filterHigh])
    Output:  The value
    -------- ------------------------------------------------------ */
-double ControllerEngine::getParameter(QString group, QString name) {
+double ControllerEngine::getParameter(const QString& group, const QString& name) {
     ControlObjectScript* coScript = getControlObjectScript(group, name);
     if (coScript == nullptr) {
         qWarning() << "ControllerEngine: Unknown control" << group << name << ", returning 0.0";
@@ -731,7 +738,8 @@ double ControllerEngine::getParameter(QString group, QString name) {
    Input:   Control group, Key name, new value
    Output:  -
    -------- ------------------------------------------------------ */
-void ControllerEngine::setParameter(QString group, QString name, double newParameter) {
+void ControllerEngine::setParameter(
+        const QString& group, const QString& name, double newParameter) {
     if (isnan(newParameter)) {
         qWarning() << "ControllerEngine: script setting [" << group << "," << name
                  << "] to NotANumber, ignoring.";
@@ -754,7 +762,8 @@ void ControllerEngine::setParameter(QString group, QString name, double newParam
    Input:   Control group, Key name, new value
    Output:  -
    -------- ------------------------------------------------------ */
-double ControllerEngine::getParameterForValue(QString group, QString name, double value) {
+double ControllerEngine::getParameterForValue(
+        const QString& group, const QString& name, double value) {
     if (isnan(value)) {
         qWarning() << "ControllerEngine: script setting [" << group << "," << name
                  << "] to NotANumber, ignoring.";
@@ -776,7 +785,7 @@ double ControllerEngine::getParameterForValue(QString group, QString name, doubl
    Input:   Control group, Key name, new value
    Output:  -
    -------- ------------------------------------------------------ */
-void ControllerEngine::reset(QString group, QString name) {
+void ControllerEngine::reset(const QString& group, const QString& name) {
     ControlObjectScript* coScript = getControlObjectScript(group, name);
     if (coScript != nullptr) {
         coScript->reset();
@@ -788,7 +797,7 @@ void ControllerEngine::reset(QString group, QString name) {
    Input:   Control group, Key name, new value
    Output:  -
    -------- ------------------------------------------------------ */
-double ControllerEngine::getDefaultValue(QString group, QString name) {
+double ControllerEngine::getDefaultValue(const QString& group, const QString& name) {
     ControlObjectScript* coScript = getControlObjectScript(group, name);
 
     if (coScript == nullptr) {
@@ -804,7 +813,7 @@ double ControllerEngine::getDefaultValue(QString group, QString name) {
    Input:   Control group, Key name, new value
    Output:  -
    -------- ------------------------------------------------------ */
-double ControllerEngine::getDefaultParameter(QString group, QString name) {
+double ControllerEngine::getDefaultParameter(const QString& group, const QString& name) {
     ControlObjectScript* coScript = getControlObjectScript(group, name);
 
     if (coScript == nullptr) {
@@ -820,7 +829,7 @@ double ControllerEngine::getDefaultParameter(QString group, QString name) {
    Input:   String to log
    Output:  -
    -------- ------------------------------------------------------ */
-void ControllerEngine::log(QString message) {
+void ControllerEngine::log(const QString& message) {
     controllerDebug(message);
 }
 
@@ -830,8 +839,9 @@ void ControllerEngine::log(QString message) {
 //          The script should store this object to call its
 //          'disconnect' and 'trigger' methods as needed.
 //          If unsuccessful, returns undefined.
-QScriptValue ControllerEngine::makeConnection(QString group, QString name,
-                                              const QScriptValue callback) {
+QScriptValue ControllerEngine::makeConnection(const QString& group,
+        const QString& name,
+        const QScriptValue& callback) {
     VERIFY_OR_DEBUG_ASSERT(m_pEngine != nullptr) {
         qWarning() << "Tried to connect script callback, but there is no script engine!";
         return QScriptValue();
@@ -889,7 +899,7 @@ void ScriptConnection::executeCallback(double value) const {
    Purpose: (Dis)connects a ScriptConnection
    Input:   the ScriptConnection to disconnect
    -------- ------------------------------------------------------ */
-bool ControllerEngine::removeScriptConnection(const ScriptConnection connection) {
+bool ControllerEngine::removeScriptConnection(const ScriptConnection& connection) {
     ControlObjectScript* coScript = getControlObjectScript(connection.key.group,
                                                            connection.key.item);
 
@@ -911,7 +921,7 @@ bool ScriptConnectionInvokableWrapper::disconnect() {
    Purpose: Triggers the callback function of a ScriptConnection
    Input:   the ScriptConnection to trigger
    -------- ------------------------------------------------------ */
-void ControllerEngine::triggerScriptConnection(const ScriptConnection connection) {
+void ControllerEngine::triggerScriptConnection(const ScriptConnection& connection) {
     if (m_pEngine == nullptr) {
         return;
     }
@@ -937,8 +947,10 @@ void ScriptConnectionInvokableWrapper::trigger() {
 // it is disconnected.
 // WARNING: These behaviors are quirky and confusing, so if you change this function,
 // be sure to run the ControllerEngineTest suite to make sure you do not break old scripts.
-QScriptValue ControllerEngine::connectControl(
-        QString group, QString name, const QScriptValue passedCallback, bool disconnect) {
+QScriptValue ControllerEngine::connectControl(const QString& group,
+        const QString& name,
+        const QScriptValue& passedCallback,
+        bool disconnect) {
     // The passedCallback may or may not actually be a function, so when
     // the actual callback function is found, store it in this variable.
     QScriptValue actualCallbackFunction;
@@ -1044,7 +1056,7 @@ QScriptValue ControllerEngine::connectControl(
    Input:   -
    Output:  -
    -------- ------------------------------------------------------ */
-void ControllerEngine::trigger(QString group, QString name) {
+void ControllerEngine::trigger(const QString& group, const QString& name) {
     ControlObjectScript* coScript = getControlObjectScript(group, name);
     if (coScript != nullptr) {
         coScript->emitValueChanged();
@@ -1130,8 +1142,7 @@ bool ControllerEngine::hasErrors(const QString& filename) {
                 whether it should fire just once
    Output:  The timer's ID, 0 if starting it failed
    -------- ------------------------------------------------------ */
-int ControllerEngine::beginTimer(int interval, QScriptValue timerCallback,
-                                 bool oneShot) {
+int ControllerEngine::beginTimer(int interval, const QScriptValue& timerCallback, bool oneShot) {
     if (!timerCallback.isFunction() && !timerCallback.isString()) {
         qWarning() << "Invalid timer callback provided to beginTimer."
                    << "Valid callbacks are strings and functions.";
@@ -1468,7 +1479,7 @@ bool ControllerEngine::isScratching(int deck) {
                 whether to set the soft-takeover status or not
     Output:  -
     -------- ------------------------------------------------------ */
-void ControllerEngine::softTakeover(QString group, QString name, bool set) {
+void ControllerEngine::softTakeover(const QString& group, const QString& name, bool set) {
     ConfigKey key = ConfigKey(group, name);
     ControlObject* pControl = ControlObject::getControl(key, onlyAssertOnControllerDebug());
     if (!pControl) {
@@ -1493,7 +1504,7 @@ void ControllerEngine::softTakeover(QString group, QString name, bool set) {
      Output:  -
      -------- ------------------------------------------------------ */
 void ControllerEngine::softTakeoverIgnoreNextValue(
-        QString group, const QString name) {
+        const QString& group, const QString& name) {
     ConfigKey key = ConfigKey(group, name);
     ControlObject* pControl = ControlObject::getControl(key, onlyAssertOnControllerDebug());
     if (!pControl) {
diff --git a/src/controllers/controllerengine.h b/src/controllers/controllerengine.h
index dad8c785bc..9caab019b7 100644
--- a/src/controllers/controllerengine.h
+++ b/src/controllers/controllerengine.h
@@ -60,7 +60,7 @@ class ScriptConnectionInvokableWrapper : public QObject {
     //Q_PROPERTY(QScriptValue function READ function)
     Q_PROPERTY(bool isConnected READ readIsConnected)
   public:
-    ScriptConnectionInvokableWrapper(ScriptConnection conn) {
+    ScriptConnectionInvokableWrapper(const ScriptConnection& conn) {
         m_scriptConnection = conn;
         m_idString = conn.id.toString();
         m_isConnected = true;
@@ -99,36 +99,39 @@ class ControllerEngine : public QObject {
     const QList<QString>& getScriptFunctionPrefixes() { return m_scriptFunctionPrefixes; };
 
     // Disconnect a ScriptConnection
-    bool removeScriptConnection(const ScriptConnection conn);
-    void triggerScriptConnection(const ScriptConnection conn);
+    bool removeScriptConnection(const ScriptConnection& conn);
+    void triggerScriptConnection(const ScriptConnection& conn);
 
   protected:
-    Q_INVOKABLE double getValue(QString group, QString name);
-    Q_INVOKABLE void setValue(QString group, QString name, double newValue);
-    Q_INVOKABLE double getParameter(QString group, QString name);
-    Q_INVOKABLE void setParameter(QString group, QString name, double newValue);
-    Q_INVOKABLE double getParameterForValue(QString group, QString name, double value);
-    Q_INVOKABLE void reset(QString group, QString name);
-    Q_INVOKABLE double getDefaultValue(QString group, QString name);
-    Q_INVOKABLE double getDefaultParameter(QString group, QString name);
-    Q_INVOKABLE QScriptValue makeConnection(QString group, QString name,
-                                            const QScriptValue callback);
+    Q_INVOKABLE double getValue(const QString& group, const QString& name);
+    Q_INVOKABLE void setValue(const QString& group, const QString& name, double newValue);
+    Q_INVOKABLE double getParameter(const QString& group, const QString& name);
+    Q_INVOKABLE void setParameter(const QString& group, const QString& name, double newValue);
+    Q_INVOKABLE double getParameterForValue(
+            const QString& group, const QString& name, double value);
+    Q_INVOKABLE void reset(const QString& group, const QString& name);
+    Q_INVOKABLE double getDefaultValue(const QString& group, const QString& name);
+    Q_INVOKABLE double getDefaultParameter(const QString& group, const QString& name);
+    Q_INVOKABLE QScriptValue makeConnection(const QString& group,
+            const QString& name,
+            const QScriptValue& callback);
     // DEPRECATED: Use makeConnection instead.
-    Q_INVOKABLE QScriptValue connectControl(QString group, QString name,
-                                            const QScriptValue passedCallback,
-                                            bool disconnect = false);
+    Q_INVOKABLE QScriptValue connectControl(const QString& group,
+            const QString& name,
+            const QScriptValue& passedCallback,
+            bool disconnect = false);
     // Called indirectly by the objects returned by connectControl