If x is stored in R (as it is by default), then this is no different than x2 <- x. But if it is stored as a pointer to a structure in C,
如果x是存储在R(因为它是默认情况下),那么这是没有什么不同比x2 < - X。但是,如果它被存储在C的结构作为一个指针,
值----------Value----------
a features object which can be modified independently from the
一个功能对象,可以独立修改