A pub-sub system used for coordinating loosely coupled systems.

GameEvent.cs

/// <summary>
/// This is a pubsub system used for coordinating loosely coupled systems.
/// It does some tricks with an internal class to improve the appearance 
/// of the public API.
/// </summary>
public static class GameEvent
{
    /* Public API */
    public static void Publish<T>(T ev) => _InternalGameEvent<T>.Publish(ev);

    public static void Subscribe<T>(System.Action<T> ev) => _InternalGameEvent<T>.Subscribe(ev);

    public static void Unsubscribe<T>(System.Action<T> ev) => _InternalGameEvent<T>.Unsubscribe(ev);

    public static void Clear<T>() => _InternalGameEvent<T>.Clear();

    /* Internal API */
    private static class _InternalGameEvent<T>
    {
        static List<System.Action<T>> subscribers = new List<System.Action<T>>();

        internal static void Publish(T ev)
        {
            for (int i = 0, count = subscribers.Count; i < count; i++)
                subscribers[i](ev);
        }

        internal static void Subscribe(System.Action<T> evListener) => subscribers.Add(evListener);

        internal static void Unsubscribe(System.Action<T> evListener)
        {
            var idx = subscribers.IndexOf(evListener);
            subscribers[idx] = subscribers[subscribers.Count - 1];
            subscribers.RemoveAt(subscribers.Count - 1);
        }

        internal static void Clear() => subscribers.Clear();
    }
}

/* Example Usage to avoid allocation:

/// <summary>
/// This class produces TouchGesture events.
/// </summary>
class TouchRecognizer {

    public struct TouchGesture {
        public Touch touch;
    }

    public void OnEventIsReady() {
        GameEvent.Publish(new TouchGesture() { touch = Input.GetTouch(0) });
    }
}

/// <summary>
/// This class consumes TouchGesture events.
/// </summary>
class TouchReceiver {

    System.Action<TouchRecognizer.TouchGesture> onTouchGesture;

    void OnEnable()
    {
        if(onTouchGesture == null)
            onTouchGesture = HandleOnTouchGesture;    
        GameEvent.Subscribe<TouchRecognizer.TouchGesture>(onTouchGesture);
    }

    void OnDisable()
    {
        GameEvent.Unsubscribe<TouchRecognizer.TouchGesture>(onTouchGesture);
    }

    void HandleOnTouchGesture(TouchRecognizer.TouchGesture gesture) {

    }
}

*/