#include <iostream>
#include <vector>

using namespace std;

int main() {
  bool guard = false;
  //-------------------------------------------------------------
  // the capture list [&] means "capture all in scope variables as
  // references.  (The list [=] means capture all as values.)
  // (The list [=,&guard] means capture all as values, except capture
  // guard as a reference.)
  //-------------------------------------------------------------
  auto f = [&](const vector<int> &lhs, const vector<int> &rhs) -> bool {
             return guard && lhs.size() < rhs.size();
           };
  auto g = f;
  cout << "guard = " << guard << endl;
  cout << f({1},{2}) << endl;
  cout << g({1},{1,2}) << endl;

  guard = true;
  cout << "guard = " << guard << endl;
  cout << f({1},{2}) << endl;
  cout << g({1},{1,2}) << endl;

  return 0;
}