Implement a singleton / static settingsManager

This change implements a QucsSingleton class that can be used to
make any class singleton. It also provides a new settingsManager
class which uses QucsSingleton to provide a single, static access
point to the standard QSettings functionality. A shortcut is provided
and a new method for providing a default value if the requested key
is not set.

qucs/CMakeLists.txt

@@ -122,6 +122,7 @@ SET(QUCS_SRCS
   mouseactions.cpp qucs_actions.cpp	schematic_file.cpp
   wirelabel.cpp node.cpp qucs_init.cpp
   syntax.cpp misc.cpp messagedock.cpp
+  settings.cpp
   imagewriter.cpp printerwriter.cpp projectView.cpp
   symbolwidget.cpp
 )
@@ -139,6 +140,7 @@ octave_window.h
 qucs.h
 qucsdoc.h
 schematic.h
+settings.h
 syntax.h
 symbolwidget.h
 textdoc.h

qucs/components/componentdialog.cpp

@@ -19,6 +19,7 @@
 #include "main.h"
 #include "qucs.h"
 #include "schematic.h"
+#include "settings.h"
 #include "misc.h"
 
 #include <cmath>
@@ -41,8 +42,13 @@
 ComponentDialog::ComponentDialog(Component *c, Schematic *d)
 			: QDialog(d)
 {
-  QSettings settings("qucs","qucs_s");
-  restoreGeometry(settings.value("ComponentDialog/geometry").toByteArray());
+  // qDebug() << "Restore: " << _settings::Get().value("ComponentDialog/geometry").toByteArray();
+  // qDebug() << "Settings: " << _settings::Get().organizationName() << " " << _settings::Get().applicationName();
+  // qDebug() << "Default test (found)" << _settings::Get().item<int>("Foo");
+  // qDebug() << "Default test (not found int type)" << _settings::Get().item<int>("Bar");
+  // qDebug() << "Default test (found wrong type)" << _settings::Get().item<QString>("Foo");
+  // qDebug() << "Default test (not found string type)" << _settings::Get().item<QString>("Bar");
+  restoreGeometry(_settings::Get().item<QByteArray>("ComponentDialog/geometry"));
 
   setWindowTitle(tr("Edit Component Properties"));
   Comp  = c;

qucs/qucs.cpp

@@ -53,6 +53,7 @@
 #include "schematic.h"
 #include "mouseactions.h"
 #include "messagedock.h"
+#include "settings.h"
 #include "wire.h"
 #include "module.h"
 #include "projectView.h"
@@ -101,6 +102,10 @@ QucsApp::QucsApp()
   QTextCodec::setCodecForLocale(QTextCodec::codecForName("UTF-8"));
 #endif
 
+  // Instantiate settings. It isn't necessary to do it at this point,
+  // but it is useful for testing.
+  _settings::Get();
+
   windowTitle = misc::getWindowTitle();
   setWindowTitle(windowTitle);
 

qucs/qucs.h

@@ -441,4 +441,33 @@ private:
   QString lastExportFilename;
 };
 
+/** \brief Provide a template to declare singleton classes.
+  *
+  * Classes implemented using this template will be singletons (i.e., only
+  * one instance of the class will exist per invokation). Primarily this
+  * is used to support static / access to an application-wide function, e.g.
+  * settings.
+  *
+  */
+template < typename T >
+class QucsSingleton final
+{
+public:
+  static T& Get()
+  {
+    static T instance;
+    return instance;
+  }
+
+// Prevent overriding default ctor, dtor, copying, or multiple instances.
+private:
+  QucsSingleton() = default;
+  ~QucsSingleton() = default;
+
+  QucsSingleton(const QucsSingleton&) = delete;
+  QucsSingleton& operator=(const QucsSingleton&) = delete;
+  QucsSingleton(QucsSingleton&&) = delete;
+  QucsSingleton& operator=(QucsSingleton&&) = delete;
+};
+
 #endif /* QUCS_H */

qucs/settings.cpp

@@ -0,0 +1,15 @@
+#include <settings.h>
+
+settingsManager::settingsManager()
+    :QSettings("qucs", "qucs_s")
+{
+    // qDebug() << this << " created " << organizationName() << " " << applicationName();
+
+    m_Defaults["Foo"] = 1234;
+
+}
+
+settingsManager::~settingsManager()
+{
+    // qDebug() << this << " destroyed";
+}

qucs/settings.h

@@ -0,0 +1,32 @@
+#include <map>
+#include <QDebug>
+#include <QSettings>
+#include <qucs.h>
+
+class settingsManager : public QSettings
+{ 
+    // Q_OBJECT
+
+// TODO: Make constructors private / protected so this class can only be
+// instantiated by QucsSingleton.
+public:
+  explicit settingsManager();
+  ~settingsManager();
+
+  template<class T>
+  T item(const QString& key)
+  {
+    if (contains(key)) {
+        return value(key).value<T>();
+    }
+    
+    else {
+        return m_Defaults[key].value<T>();
+    }
+  }
+
+private:
+  std::map<QString, QVariant> m_Defaults;
+};
+
+typedef QucsSingleton<settingsManager> _settings;