/*
   File essential.cpp                      shinnerl@ucla.edu
   Example illustrating automatic calls to 
   the essential member functions:
        1) Default constructor 
        2) Copy constructor 
        3) Destructor
        4) Assignment operator
   Note that there is no need for our class X to have 
   any data members here.
*/

#include <iostream>
using namespace std;

class X{
  public:
     X()           { cout << "Class X default constructor called!\n"; }
     X(const X& x) { cout << "Class X copy constructor called!\n"; }
     ~X()          { cout << "Class X destructor called!\n"; }
     const X& operator=(const X& ); 
};

const X& X::operator=(const X& rhs) { 
   cout << "Class X assignment operator called!\n"; 
   return *this;
}

class Y {public: X x; };  // Each instance of class Y has an instance 
                          // of class X as a member.


X foo(X x0){     // Receives an X by value and returns
  return x0;     //  it by value, causing two copy-constructor calls.
}
                
int main(){
   X x1, x2;           // Two calls to the default constructor for X.
   Y y1, y2;           // Two calls to the default constructor for Y 
                       //  (and hence, to the default constructor for X also).
   foo(x1);            // Two calls to the copy constructor for X.
   y2 = y1;            // Assignment for Y is memberwise (shallow copy); 
                       // hence, assignment for X also.
   return 0;
}                      // Four calls to the destructor for X.

/* Output:
whale.77> a.out
Class X default constructor called!
Class X default constructor called!
Class X default constructor called!
Class X default constructor called!
Class X copy constructor called!
Class X copy constructor called!
Class X destructor called!
Class X destructor called!
Class X assignment operator called!
Class X destructor called!
Class X destructor called!
Class X destructor called!
Class X destructor called!
whale.78>
*/