13.27.cpp

#include <string>
#include <iostream>

// Pointerlike version
class HasPtr {
public:
  HasPtr(const std::string &s = std::string())
      : ps(new std::string(s)), i(0), use(new std::size_t(1)) {}
  HasPtr(const HasPtr &ori)
      : ps(ori.ps), i(ori.i), use(ori.use) { ++*use; }
  ~HasPtr();

  HasPtr &operator=(const HasPtr &rhs);

  const std::string &get() const { return *ps; }
  void set(const std::string &s) { *ps = s; }

private:
  std::string *ps;
  int i;
  std::size_t *use;
};

HasPtr::~HasPtr() {
  if (--*use == 0) {
    delete ps;
    delete use;
  }
}

HasPtr &HasPtr::operator=(const HasPtr &rhs) {
  ++*rhs.use;
  if (--*use == 0) {
    delete ps;
    delete use;
  }
  ps = rhs.ps;
  i = rhs.i;
  use = rhs.use;
  return *this;
}

int main() {
  HasPtr hp1 = "World";
  HasPtr hp2 = hp1;
  HasPtr hp3;
  hp3 = hp1;
  hp1.set("Hello");

  std::cout << hp1.get() << std::endl;
  std::cout << hp2.get() << std::endl;
  std::cout << hp3.get() << std::endl;

  hp1 = hp1;
  std::cout << "After `hp1 = hp1`: " << hp1.get() << std::endl;

  return 0;
}