Header-only C++20 simple and fast event bus

Description

• EventManager is a singleton.

• All events must inherit the EventBase class. Due to this, a mechanism is provided to stop notifying the remaining receivers.

• All event receivers must inherit the EventReceiver class. When the event receiver is destroyed, he automatically unsubscribes from all events.

• The event receiver subscribes to the event by passing a reference to itself and a pointer to the method that handles the event, or the corresponding lambda expression.

• Unsubscribing occurs by passing the event type and a pointer to the event receiver; it is also possible to unsubscribe from all events at once.

• You can schedule an urgent action which is a one-time callback for the next (any) event or an event action which is a one-time callback for a specific type of event.

Example

#define self *this

class App
{
public:
    class E_Update : public el::EventBase
    {
    public:
        explicit E_Update() = default;
    }

    class E_PreTick : public el::EventBase
    {
    public:
        float deltaTime;

        explicit E_PreTick(float theDeltaTime) :
            deltaTime(theDeltaTime) { }
    }

    class E_Tick : public el::EventBase
    {
    public:
        float deltaTime;

        explicit E_Tick(float theDeltaTime) :
            deltaTime(theDeltaTime) { }
    }

    void run()
    {
        EVENT_MANAGET_GET(); // auto& EM = el::EventManager::get();

        // ...

        EM.publish(E_Update());

        // ...

        EM.publish(E_PreTick(dt));

        EM.publish(E_Tick(dt));

        // ...
    }
}

class MyReceiver : el::EventReceiver
{
public:
    virtual ~MyReceiver() = default;

protected:
    MyReceiver()
    {
        // EM is inherited
        EM.subscribe(self, &MyReceiver::onUpdate);
    }

    virtual void onUpdate(App::E_Update const& e)
    {
        // ...
    }
};

class Actor : public MyReceiver
{
public:
    Actor()
    {
        EM.subscribe(self, &Actor::onTick);

        EM.subscribe<App::E_PreTick>(
            [this](App::E_PreTick const& e)
            {
                // ...
            }
        );

        EM.unsubscribe<App::E_Tick>(self);
    }
    
    void doSomething()
    {
        EM.schedule<App::E_Update>( // a one-time callback
            [this]
            {
                // ...
            }
        );

        EM.schedule(                // an urgent action
            [this]
            {
                // ...
            }
        );
    }

private:
    void onTick(App::E_Tick const& e)
    {
        // ...

        if (/* requires stopping informing other receivers */)
            e.handled = true; // handled is mutable
    }
};

License

This project is under MIT License.

Copyright (c) 2025 3lyrion

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.