CObservable.h

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/* +------------------------------------------------------------------------+
   |                     Mobile Robot Programming Toolkit (MRPT)            |
   |                          https://www.mrpt.org/                         |
   |                                                                        |
   | Copyright (c) 2005-2020, Individual contributors, see AUTHORS file     |
   | See: https://www.mrpt.org/Authors - All rights reserved.               |
   | Released under BSD License. See: https://www.mrpt.org/License          |
   +------------------------------------------------------------------------+ */
#pragma once

#include <set>

namespace mrpt::system
{
class CObserver;
class mrptEvent;

/** Inherit from this class for those objects capable of being observed by a
 * CObserver class.
 *
 *  The only thing to do in your child class is to call
 * CObservable::publishEvent() whenever needed and all the
 *   observer classes will be notified.
 *
 * \note The pairs CObservable / CObserver automatically notify each other the
 * destruction of any of them, effectively ending the subscription of events.
 *
 *  \sa CObserver, mrptEvent
 * \ingroup mrpt_system_grp
 */
class CObservable
{
    friend class CObserver;

   public:
    CObservable();
    virtual ~CObservable();

   private:
    std::set<CObserver*> m_subscribers;
    void internal_observer_begin(CObserver*);
    void internal_observer_end(CObserver*);

   protected:
    /** Called when you want this object to emit an event to all the observers
     * currently subscribed to this object. */
    void publishEvent(const mrptEvent& e) const;

    /** Can be called by a derived class before preparing an event for
     * publishing with \a publishEvent to determine if there is no one
     *  subscribed, so it can save the wasted time preparing an event that will
     * be not read. */
    inline bool hasSubscribers() const { return !m_subscribers.empty(); }
};  // End of class def.

}  // namespace mrpt::system