signal

signal is a small header-only C++20 signal/slot library in the sg namespace. It provides ordered listener dispatch, RAII disconnection, and safe mutation during emit, including self-disconnect, disconnecting other listeners, and nested emits.

Requirements

• C++20
• Header-only
• Single-threaded use only

This version does not provide thread safety, combiners, result aggregation, slot grouping, or blocking.

Integration

CMake

find_package(signal CONFIG REQUIRED)
target_link_libraries(your_target PRIVATE sg::signal)

Direct include

Copy the headers from src/ into your include path and include:

#include <sg.hpp>

Basic usage

#include <sg.hpp>
#include <iostream>

int main() {
    sg::Signal<int> value_changed;

    sg::ScopedConnection log_connection(
        value_changed.connect([](int value) {
            std::cout << "value: " << value << '\n';
        }));

    auto oneshot = value_changed.connect([&](int value) {
        std::cout << "first and only: " << value << '\n';
    });

    value_changed.emit(7);
    oneshot.disconnect();
    value_changed(9);
}

Behavior notes

• Listeners run in registration order.
• Disconnecting the current listener or another listener during emit is safe.
• New listeners added during an emit are not invoked by that active emit; they participate in later emits.
• Nested emits are supported. Each emit observes the listener list visible when that emit begins.
• sg::Connection is move-only and disconnects on destruction.
• sg::ScopedConnection wraps a Connection and disconnects automatically unless release() transfers ownership.

Public API

• sg::Signal<Args...>
• sg::Connection
• sg::ScopedConnection

Core methods:

• connect(...)
• emit(...)
• operator()(...)
• disconnect_all()
• empty()
• size()
• listener_count()
• disconnect()
• connected()
• reset()
• release()