#include <string>
#include <iostream>
#include <vector>

template<typename T>
class stack {
public:
  auto push(T const&) -> void;
  auto pop() -> void;

  friend auto operator<<(std::ostream& os, stack<T> const& s) -> std::ostream& {
    return os << "My top item is " << s.stack_.back() << "\n";
  }

private:
  std::vector<T> stack_;
};

template<typename T>
auto stack<T>::push(T const& t) -> void {
  stack_.push_back(t);
}

auto main() -> int {
  stack<std::string> ss;
  ss.push("Hello");
  std::cout << ss << "\n";

  stack<int> is;
  is.push(5);
  std::cout << is << "\n";
}