Don't use Preferences in BitTorrent::Session

src/base/settingvalue.h

@@ -0,0 +1,73 @@
+/*
+ * Bittorrent Client using Qt and libtorrent.
+ * Copyright (C) 2016  Vladimir Golovnev <glassez@yandex.ru>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ *
+ * In addition, as a special exception, the copyright holders give permission to
+ * link this program with the OpenSSL project's "OpenSSL" library (or with
+ * modified versions of it that use the same license as the "OpenSSL" library),
+ * and distribute the linked executables. You must obey the GNU General Public
+ * License in all respects for all of the code used other than "OpenSSL".  If you
+ * modify file(s), you may extend this exception to your version of the file(s),
+ * but you are not obligated to do so. If you do not wish to do so, delete this
+ * exception statement from your version.
+ */
+
+#ifndef SETTINGVALUE_H
+#define SETTINGVALUE_H
+
+#include <functional>
+#include <QString>
+
+#include "settingsstorage.h"
+
+template <typename T>
+class CachedSettingValue
+{
+    using ProxyFunc = std::function<T (const T&)>;
+
+public:
+    explicit CachedSettingValue(const char *keyName, const T &defaultValue = T()
+            , ProxyFunc proxyFunc = [](const T &value) { return value; })
+        : m_keyName(QLatin1String(keyName))
+        , m_value(proxyFunc(SettingsStorage::instance()->loadValue(
+                                m_keyName, defaultValue).template value<T>()))
+    {
+    }
+
+    T value() const
+    {
+        return m_value;
+    }
+
+    CachedSettingValue<T> &operator=(const T &newValue)
+    {
+        m_value = newValue;
+        SettingsStorage::instance()->storeValue(m_keyName, m_value);
+        return *this;
+    }
+
+    operator T() const
+    {
+        return value();
+    }
+
+private:
+    const QString m_keyName;
+    T m_value;
+};
+
+#endif // SETTINGVALUE_H