constructors_demo.cpp

#include <iostream>

void copy_mem(const int *from, int *to, int n) {
  std::cout << "copy memory from " << from << " into " << to << std::endl;
  for (int i = 0; i < n; i++) {
    to[i] = from[i];
  }
}

class Box {

 public:
  int n_;
  int *arr_;

  explicit Box(int n) : n_(n), arr_(new int[n]) {
    std::cout << "New Box(" << n << ") at" << this << std::endl;
  }

  Box(const Box &box) : n_(box.n_), arr_(new int[box.n_]) {
    std::cout << "Copy Box(" << box.n_ << ") from " << &box << " into " << this << std::endl;
    copy_mem(box.arr_, arr_, box.n_);
  }

  Box(Box &&box) noexcept : n_(box.n_), arr_(box.arr_) {
    std::cout << "Move from " << &box << " into " << this << std::endl;
    box.arr_ = nullptr;
    box.n_ = 0;
  }

  Box &operator=(const Box &box) {
    if (this == &box) return *this; // self assignment check
    std::cout << "Assignment operator " << this << "=" << &box << std::endl;
    delete [] arr_;
    arr_ = new int[box.n_];
    copy_mem(box.arr_, arr_, box.n_);
    n_ = box.n_;
    return *this;
  }

  ~Box() {
    std::cout << "Delete ~Box(" << n_ << ") " << this << std::endl;
    delete [] arr_;
  }
};

int main() {
  {
    std::cout << "==========EXAMPLE 1=========" << std::endl;
    // Copy constructor example
    Box b(100);
    Box b2 = b;
  }
  {
    std::cout << "==========EXAMPLE 2=========" << std::endl;
    // Assignment operator example
    Box a(100);
    Box a2(42);
    a2 = a;
  }
  {
    std::cout << "==========EXAMPLE 3=========" << std::endl;
    // Self Assignment
    Box c(13);
    c = c;// wtf
  }
  {
    std::cout << "==========EXAMPLE 4=========" << std::endl;
    Box d(17);
    assert(d.n_ == 17);
    Box d2(std::move(d));
    assert(d.n_ == 0);
    assert(d.arr_ == nullptr);
    assert(d2.n_ == 17);
  }

  std::cout << "FINISH" << std::endl;
  return 0;
}