/// <summary>
/// Iterates throw the exception (considering inner exceptions, aggregate exceptions)
/// </summary>
/// <param name="ex"></param>
/// <returns></returns>
public static IEnumerable <Exception> Flatten(this Exception ex) =>
TreeIterator <Exception> .New().Flatten(ex, e =>
(e as AggregateException).IfExists(aggregate => aggregate.InnerExceptions)
?? e.InnerException.IfExists(inner => inner.Once())
?? Enumerable.Empty <Exception>());
