public static IEnumerable <MessageAbstraction> AttachMessage(this IEnumerable <MessageAbstraction> messages, MessageAbstraction otherMessage) => messages.Append(otherMessage);
public static IEnumerable <MessageAbstraction> AttachMessage(this MessageAbstraction message, MessageAbstraction otherMessage) => new[] { message, otherMessage };
public static IEnumerable <MessageAbstraction> AttachMessages(this MessageAbstraction message, IEnumerable <MessageAbstraction> otherMessages) => new[] { message }.AttachMessages(otherMessages);