#include <utility>
#include <string>
#include <iostream>

template <typename T>
int count();

template <typename T>
class Tracker : public T
{
public:

  template <typename... Args>
  Tracker(Args&&... args)
    : T(std::forward<Args>(args)...)
  {
    ++counter;
  }

  ~Tracker()
  {
    --counter;
  }
  
  Tracker(Tracker<T> const& other)
    : T{other}
  {
    ++counter;
  }

  Tracker(Tracker<T>&&) = default;

  Tracker<T>& operator=(Tracker<T> const& other)
  {
    Tracker<T> tmp{other};
    return *this = std::move(tmp);
  }
  
private:
  static int counter;
  
  friend int count<T>();
  
};

template <typename T>
int Tracker<T>::counter{0};

template <typename T>
int count()
{
  return Tracker<T>::counter;
}

struct Hello_Worlder
{
  std::string get()
  {
    return "hello world!";
  }
};

/* The output should be:

0
str1 str2
hello world!
++++++++++
3
1
2

*/

int main()
{
  using std::cout;
  using std::endl;
  using std::string;

  cout << count<string>() << endl;
  
  Tracker<string> str1{};
  str1 += "str1";
  for (char c : str1)
  {
    cout << c;
  }
  Tracker<string> str2{"str2"};
  cout << " " << str2 << endl;

  Tracker<Hello_Worlder> hw{};
  cout << hw.get() << endl;

  {
    Tracker<string> str3(10u, '+');
    cout << str3 << endl;
    cout << count<string>() << endl;
  }
  cout << count<Hello_Worlder>() << endl;
  cout << count<string>() << endl;
  
}