boost::variant recursive trouble

问题

is there any way to make this work? I hope you'll get the idea, I'm trying to create a list by means of recursive pairs

#include <boost/variant.hpp>
#include <utility>

struct nil {};
typedef boost::make_recursive_variant<nil, std::pair<int, boost::recursive_variant_ >>::type list_t;

int main() {
  list_t list = { 1, (list_t){ 2, (list_t){ 3, nil() } } };
  return 0;
}

回答1:

No. The point of a boost::variant is that it has a fixed size, and does not do dynamic allocation. In this way it's similar to a union. A recursive boost::variant would have to have infinite size in order to contain its largest possible value - clearly impossible.

You could, however, do this by passing it through a pointer. For example:

struct nil { };

typedef boost::make_recursive_variant<nil, 
    std::pair<int, boost::scoped_ptr<boost::recursive_variant_> > >
        variant_list_int;

来源：https://stackoverflow.com/questions/4932208/boostvariant-recursive-trouble