Simple Event C++

A lightweight, header-only C++ event system with subscription lifetime management.

Features

• Header-only — drop Event.h into your project
• Type-safe — template-based event arguments with full type checking
• RAII subscriptions — EventSubscription automatically unsubscribes on destruction
• Move semantics — events and subscriptions are movable, not copyable
• Reentrancy-safe — subscribers can safely unsubscribe during event firing
• Priority-based dispatch — subscribers can specify execution order
• C++11–C++20 compatible, uses concepts when available

Usage

#include "Event.h"

#include <string_view>

class MyClassProvidingEvent {
public:
    /// Expose event Observer to subscribers!
    auto& eventTest() const noexcept { return eventTest_.observer(); }
    auto& eventWithData() const noexcept { return eventWithData_.observer(); }

    void fireEvents()
    {
        eventTest_.fire();
        eventWithData_.fire("Your answer", 42);
    }
private:
    Event<> eventTest_;
    Event<std::string_view, int> eventWithData_;
};

MyClassProvidingEvent myClass;

// Subscribe
const auto sub1 = myClass.eventTest().subscribe([]() {
    std::cout << "Simple event received" << std::endl;
});

const auto sub2 = myClass.eventWithData().subscribe([](std::string_view d1, int d2) {
    std::cout << "Event with data received: " << d1 << ", " << d2 << std::endl;
});

// Fire
myClass.fireEvents();

// Subscription auto-unsubscribes when `sub` goes out of scope

Build

cmake -G Ninja -B build
cmake --build build
./build/tests

Example CMakeLists.txt requires CMake 3.20+ and a C++20-compatible compiler.