// B6.cpp - describe all of the resulting operations

#include <iostream>
using namespace std;

class X { 
  public:
////// compiler generated void and copy work correctly ///////
//  X() { cout << "\n  constructing void base object"; }
//  X(const X &x) { cout << "\n  copying base object"; }
    virtual void mf() { cout << "\n  X::mf()"; } 
}; 

class Y : public X { 
  public: 
////// compiler generated void and copy work correctly ///////
//  Y() : X() { cout << "\n  derived void construction"; }
//  Y(const Y &y) : X(y) { cout << "\n  derived copy operation"; }
    virtual void mf() { cout << "\n  Y::mf()"; }
};
 
X aFunction(X &x) { x.mf(); return x; }

// Describe everything that happens when the following code is executed?  
// Please be as complete as possible in describing what happens to the 
// objects x and y, below.

void main() {
 
/////////////////////////////////////////////////////////////////////////////
// In statement below:
// - void compiler generated constructor for Y is called to initialize y;
// - It calls, as its first act, compiler generated void constructor, X(), 
//   for its base part.
  
  Y y; 

////////////////////////////////////////////////////////////////////////////
// In the statement below:
// - y is passed by reference to aFunction, so no constructor is called here.
// - x.mf() inside aFunction results in a call to Y::mf().
// - x, a reference to the derived object y, is returned by value, so a copy
//   is made using the compiler generated base class copy constructor 
//   X(const X &s);
// - A new X object, x, is created with a call to the X class copy constructor
// - temporary X object is destroyed with X::~X().
// Note that compiler optimization will probably result in only one call to
// the X copy constructor begin made for the return and creation of x.

  X x = aFunction(y);

  cout << "\n\n";
}