copy-cons.cpp

#include <iostream>
using namespace std;

class X {
    public:
        int i;
        
        // ordinary cons X y(5):
        X(int x) : i(x) { cout << "constructor " << i; }
        
        // default cons X x:
        X() { cout << "default constructor set i=99 "; i = 99; }
        
        // copy cons X z(y):
        //X(const X&) {
        X(const X& a) {
            i = a.i * 2;
            cout << "copy constructor " << i << " " << a.i << " ";
        }
        
        // move cons X c(std::move(x))
        X(X&& x) {
            cout << "move constructor " << x.i << " ";
        }
        
        // copy assignment y = x
        X& operator=(const X& x) {
            i = x.i+1;
            cout << "copy assignment(+1) " << x.i << " ";
        }
        
        // move assignment
        X& operator=(X&& x) {
            cout << "move assignment " << x.i << " ";
        }
};

// return copy elision
X& f() {
    X x;
    int i;
    int* ip = new int;
    cout << "f: x.i " << x.i << " &x " << &x << " &i " << &i << " ip " << ip << " ";
    return x;
}

int* return_intptr() {
    int i;
    cout << "return_intptr &i " << &i << " ";
    return &i;
}

int main() {
    int i;
	cout << __LINE__ << " ";    X y(5); cout << endl;
	cout << __LINE__ << " ";    X x; cout << x.i << endl;
	cout << __LINE__ << " ";    y = x; cout << y.i << endl;
	cout << __LINE__ << " ";    X z(y); cout << z.i << endl;
	cout << __LINE__ << " ";    x.i = 77; cout << endl;
	cout << __LINE__ << " ";    y = std::move(x); cout << endl;
	cout << __LINE__ << " ";    X& a = f(); cout << "&a.i " << &a.i << " &i " << &i << endl;
	cout << __LINE__ << " ";    X mc(f()); cout << endl;
	cout << __LINE__ << " ";    cout << y.i << endl;
	cout << __LINE__ << " ";    int* ip = return_intptr(); cout << "&ip " << ip << endl;
	return 0;
}