settingvalue.h

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/*
 * Bittorrent Client using Qt and libtorrent.
 * Copyright (C) 2016  Vladimir Golovnev <[email protected]>
 *
 * 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.
 */
 
#pragma once
 
#include <QString>
 
#include "settingsstorage.h"
 
// This is a thin/handy wrapper over `SettingsStorage`. Use it when store/load value
// rarely occurs, otherwise use `CachedSettingValue`.
template <typename T>
class SettingValue
{
public:
    explicit SettingValue(const char *keyName)
        : m_keyName {QLatin1String {keyName}}
    {
    }
 
    T get(const T &defaultValue = {}) const
    {
        return SettingsStorage::instance()->loadValue(m_keyName, defaultValue);
    }
 
    operator T() const
    {
        return get();
    }
 
    SettingValue<T> &operator=(const T &value)
    {
        SettingsStorage::instance()->storeValue(m_keyName, value);
        return *this;
    }
 
private:
    const QString m_keyName;
};
 
template <typename T>
class CachedSettingValue
{
public:
    explicit CachedSettingValue(const char *keyName, const T &defaultValue = {})
        : m_setting {keyName}
        , m_cache {m_setting.get(defaultValue)}
    {
    }
 
    // The signature of the ProxyFunc should be equivalent to the following:
    // T proxyFunc(const T &a);
    template <typename ProxyFunc>
    explicit CachedSettingValue(const char *keyName, const T &defaultValue, ProxyFunc &&proxyFunc)
        : m_setting {keyName}
        , m_cache {proxyFunc(m_setting.get(defaultValue))}
    {
    }
 
    T get() const
    {
        return m_cache;
    }
 
    operator T() const
    {
        return get();
    }
 
    CachedSettingValue<T> &operator=(const T &value)
    {
        if (m_cache == value)
            return *this;
 
        m_setting = value;
        m_cache = value;
        return *this;
    }
 
private:
    SettingValue<T> m_setting;
    T m_cache;
};