src/base/settingvalue.h

   1 /*
   2  * Bittorrent Client using Qt and libtorrent.
   3  * Copyright (C) 2016  Vladimir Golovnev <glassez@yandex.ru>
   4  *
   5  * This program is free software; you can redistribute it and/or
   6  * modify it under the terms of the GNU General Public License
   7  * as published by the Free Software Foundation; either version 2
   8  * of the License, or (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License
  16  * along with this program; if not, write to the Free Software
  17  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
  18  *
  19  * In addition, as a special exception, the copyright holders give permission to
  20  * link this program with the OpenSSL project's "OpenSSL" library (or with
  21  * modified versions of it that use the same license as the "OpenSSL" library),
  22  * and distribute the linked executables. You must obey the GNU General Public
  23  * License in all respects for all of the code used other than "OpenSSL".  If you
  24  * modify file(s), you may extend this exception to your version of the file(s),
  25  * but you are not obligated to do so. If you do not wish to do so, delete this
  26  * exception statement from your version.
  27  */
  28
  29 #pragma once
  30
  31 #include <QString>
  32
  33 #include "settingsstorage.h"
  34
  35 // This is a thin/handy wrapper over `SettingsStorage`. Use it when store/load value
  36 // rarely occurs, otherwise use `CachedSettingValue`.
  37 template <typename T>
  38 class SettingValue
  39 {
  40 public:
  41     explicit SettingValue(const char *keyName)
  42         : m_keyName {QLatin1String {keyName}}
  43     {
  44     }
  45
  46     T get(const T &defaultValue = {}) const
  47     {
  48         return SettingsStorage::instance()->loadValue(m_keyName, defaultValue);
  49     }
  50
  51     operator T() const
  52     {
  53         return get();
  54     }
  55
  56     SettingValue<T> &operator=(const T &value)
  57     {
  58         SettingsStorage::instance()->storeValue(m_keyName, value);
  59         return *this;
  60     }
  61
  62 private:
  63     const QString m_keyName;
  64 };
  65
  66 template <typename T>
  67 class CachedSettingValue
  68 {
  69 public:
  70     explicit CachedSettingValue(const char *keyName, const T &defaultValue = {})
  71         : m_setting {keyName}
  72         , m_cache {m_setting.get(defaultValue)}
  73     {
  74     }
  75
  76     // The signature of the ProxyFunc should be equivalent to the following:
  77     // T proxyFunc(const T &a);
  78     template <typename ProxyFunc>
  79     explicit CachedSettingValue(const char *keyName, const T &defaultValue, ProxyFunc &&proxyFunc)
  80         : m_setting {keyName}
  81         , m_cache {proxyFunc(m_setting.get(defaultValue))}
  82     {
  83     }
  84
  85     T get() const
  86     {
  87         return m_cache;
  88     }
  89
  90     operator T() const
  91     {
  92         return get();
  93     }
  94
  95     CachedSettingValue<T> &operator=(const T &value)
  96     {
  97         if (m_cache == value)
  98             return *this;
  99
 100         m_setting = value;
 101         m_cache = value;
 102         return *this;
 103     }
 104
 105 private:
 106     SettingValue<T> m_setting;
 107     T m_cache;
 108 };