C++ thread "attempt to use a deleted function" error [duplicate]

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• std::thread pass by reference calls copy constructor 2 answers

I'm getting the error when creating a thread. I guess I'm not clear about how C++ implicitly use the "delete" function. Following is the program, I declared a struct, a function, and the main:

struct refo {
  int n;
  refo(int m):n(m) {
    auto id = this_thread::get_id();
    cout << id << ":created:" << n << endl;
  }

  ~refo() {
    auto id = this_thread::get_id();
    cout << id << ":destroyed" << n << endl;
  }
}
void testReference2(vector<refo>& v) {
  this_thread::sleep_for(chrono::seconds(3));
  cout << "v size:" << v.size() << endl;
}

int main() {
    vector<refo> v;
    std::thread t(testReference2, v); //<--- error here
    t.join();
    return 0;
}

But I'm getting a link error: /Applications/http://ift.tt/1MCHFEE: error: attempt to use a deleted function

I guess this is C++ newbie question but thanks for any help!