Settings class with "magic" enums (QSettings wrapper)

settings.cpp

#include "settings.h"
#include <QSettings>
#include <QMetaEnum>
#include <QRegExp>
#include <QStringList>

Settings::Settings(){
    const QMetaObject &mo = staticMetaObject;
    int idx = mo.indexOfEnumerator("Key");
    keys = mo.enumerator(idx);

    idx = mo.indexOfEnumerator("Section");
    sections = mo.enumerator(idx);
}

QVariant Settings::get(Key k, Section s){
    Settings &self = instance();
    QString key = self.keyPath(s, k);
    return self.conf.value(key, self.defaults[key]);
}

Settings::ValueRef Settings::set(Key k, Section s){
    Settings &self = instance();
    return ValueRef(self, self.keyPath(s, k));
}

void Settings::setDefaults(const QString &str){
    Settings &self = instance();

    // section/key : value;
    // section - optional
    QRegExp rxRecord("^\\s*(((\\w+)/)?(\\w+))\\s*:\\s*([^\\s].{0,})\\b\\s*$");

    auto kvs = str.split(QRegExp(";\\W*"), QString::SkipEmptyParts); //key-values
    for(auto kv : kvs){
        if(rxRecord.indexIn(kv) != -1){
            QString section = rxRecord.cap(3);
            QString key = rxRecord.cap(4);
            QString value = rxRecord.cap(5);

            int iKey = self.keys.keyToValue(key.toLocal8Bit().data());
            if(iKey != -1){
                int iSection = self.sections.keyToValue(section.toLocal8Bit().data());
                if(section.isEmpty() || iSection != -1){
                    self.defaults[rxRecord.cap(1)] = value;
                }
            }
        }
    }
}

//Settings::ValueRef-----------------------------------------------------------
Settings::ValueRef &Settings::ValueRef::operator = (const QVariant &data){
    parent.conf.setValue(keyPath, data);
    return *this;
}


//PRIVATE METHODS--------------------------------------------------------------
QString Settings::keyPath(Section s, Key k){
    auto szSection = sections.valueToKey(s);
    auto szKey = keys.valueToKey(k);
    return QString(s == General ? "%1" : "%2/%1").arg(szKey).arg(szSection);
}

Settings & Settings::instance(){
    static Settings singleton;
    return singleton;
}

settings.h

#ifndef SETTINGS_H
#define SETTINGS_H

#include <QVariant>
#include <QSettings>
#include <QMetaEnum>

/**
  @brief Configuration access singleton

  Usage:
  @code
    ...
    ...
    //must be predefined somewhere in main
    QApplication::setOrganizationName("Organization name");
    QApplication::setApplicationName("App name");
    ...
    ...
    //default values can be configured by calling (config-string can be multyline):
    Settings::setDefaults("SomeKey: value1; SomeSection/SomeKey: value2");

    //or
    QFile f(":/defaults/config");
    f.open(QIODevice::ReadOnly);
    Settings::setDefaults(f.readAll());
    ...
    ...
    void fun(){
        ...
        QVariant val1 = Settings::get(Settings::SomeKey);
        Settings::set(Settings::SomeKey) = "new val1";
        ...
        QVariant val2 = Settings::get(Settings::SomeKey, Settings::SomeSection);
        Settings::set(Settings::SomeKey, Settings::SomeSection) = "new val2";
        ...
    }
  @endcode

  Sections and keys can be modified by changing enums only! (the class itself does not need to change)
*/
class Settings{
    Q_GADGET
    Q_ENUMS(Section)
    Q_ENUMS(Key)
public:
    enum Section{
        General,       //this is default section
        SomeSection1,
        SomeSection2
    };

    enum Key{
        SomeKey1,
        SomeKey2
    };

    class ValueRef{
    public:
        ValueRef(Settings &st, const QString &kp) :
            parent(st), keyPath(kp){}
        ValueRef & operator = (const QVariant &d);
    private:
        Settings &parent;
        const QString keyPath;
    };

    static void setDefaults(const QString &str);
    static QVariant get(Key, Section /*s*/ = General);
    static ValueRef set(Key, Section /*s*/ = General);

private:
    QString keyPath(Section, Key);

    static Settings & instance();
    QMetaEnum keys;
    QMetaEnum sections;
    QMap<QString, QVariant> defaults;
    QSettings conf;

    Settings();
    Settings(const Settings &);
    Settings & operator = (const Settings &);
};

#endif // SETTINGS_H

for more details see the post