boost :: variant递归麻烦 [英] boost::variant recursive trouble

问题描述

有没有办法让这项工作？我希望你会得到的想法，我想通过递归对创建一个列表

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;
}

推荐答案

boost :: variant的一点是它有固定的大小，不做动态分配。这样，它就像一个联合。递归boost ::变体必须具有无限大小，以便包含其最大可能的值 - 显然是不可能的。

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.

然而，你可以通过传递它指针。例如：

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;

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