Why can't I have std::vector<json&> testList?

[sreerajchundayil]

This works.

#include "json.h"
#include <vector>
using json = nlohmann::json;

int main()
{
  std::vector<json> testList;
}

This also works.

#include "json.h"
#include <vector>
using json = nlohmann::json;

int main()
{
  std::vector<json*> testList;
}

This doesn't. Gives compile error. Why?

#include "json.h"
#include <vector>
using json = nlohmann::json;

int main()
{
  std::vector<json&> testList;
}

[nlohmann]

This is unrelated to the library: https://stackoverflow.com/questions/8200701/vectors-of-references-to-objects