Vector class

We should implement a vector class, using std:vector from C++, which would allow adding new items to a vector with amortized constant complexity (it would solve a "dynamically extending vector" problem).

The main question is: should it be a vector of any R objects (it would be like an R list), or maybe one type of objects (more like an R vector)?

And is there any way to implement operator [], like vector[5]? Or the only way is to make a function get_element(vector, 5) and set_element(vector, 5)?