/*
How is a data structure like vector defined?
*/
#include<iostream>
#include<vector>
using namespace std;

template<typename T>
struct myvector{
  T* V;
  int len;
  myvector(int n) {len=n; V = new T[n];}
  myvector(initializer_list<T> M) {
    len = M.size();
    V = new T[len];
    int i=0;
    for (T x:M) V[i++] = x;
  }
  ~myvector() { if (V) delete[] V; }    // destructor
  T& operator [] (int i) {return V[i];}
  int size() { return len; }

  // the default copy semantics copies just the pointer when a copy
  // occurs (a = b).  This is not a good idea because when the
  // destructors of the two copies of myvector are called, the same
  // data is deleted twice.

  // define custom copy semantics
  myvector(const myvector<T>& other) {  // copy constructor
    len = other.len;
    V = new T[len]; // recreate another array on heap
    for(int i=0;i<len;i++) V[i] = other.V[i];
  }
  myvector<T>& operator =(const myvector<T>& other) {  // copy = operator
    len = other.len;
    V = new T[len]; // recreate another array on heap
    for(int i=0;i<len;i++) V[i] = other.V[i];
    return other;
  }

  // define custom MOVE SEMANTICS
  myvector(myvector<T>&& other) {  // MOVE constructor
    len = other.len;
    if (V) delete[] V;
    V = other.V;
    other.V = nullptr;
    other.len = 0;
  }
  void operator =(myvector<T>&& other) {  // MOVE = operator
    len = other.len;
    if (V) delete[] V;
    V = other.V;
    other.V = nullptr;
    other.len = 0;
  }  
  
  // push_back requires reallocating the vector..
};

int main() {
  vector<int> v1{2,4,6,8};
  vector<int> v2 = v1; // is the data copied, or just a pointer copied?
  v2[3] = 9;
  cout << v1[3] << " and " << v2[3] << endl;

  myvector<int> m1{1,3,5,7};
  myvector<int> m2 = m1;
  m2[3] = 9;
  cout << m2[3] << endl;  
  cout << m1[3] << endl;
  return 0;
}

// program illustrating custom copy semantics in traditional C++