Mediator.cs

public TResult Send<TResult>(ICommand<TResult> message)
{
    var defaultHandler = GetHandler(message);

    TResult result = defaultHandler.Handle(message);

    var eventHandlers = GetEventHandlers(message);

    foreach (var eventHandler in eventHandlers)
    {
        eventHandler.Handle(message, result);
    }

    return result;
}

public TResponse Request<TResponse>(IQuery<TResponse> query)
{
    var handler = GetHandler(query);

    return handler.Handle(query);
}