应该是 Law of Demeter, quote from [wikipedia](
https://en.wikipedia.org/wiki/Law_of_Demeter): an object should avoid invoking methods of a member object returned by another method. For many modern object oriented languages that use a dot as field identifier, the law can be stated simply as "use only one dot". That is, the code a.b.Method() breaks the law where a.Method() does not. As an analogy, when one wants a dog to walk, one does not command the dog's legs to walk directly; instead one commands the dog which then commands its own legs.