constret.cpp

Thinking in C++ 2nd edition source code which are all the cores of the book Thinking in C++ second e

//: C08:Constret.cpp
// From Thinking in C++, 2nd Edition
// at http://www.BruceEckel.com
// (c) Bruce Eckel 1999
// Copyright notice in Copyright.txt
// Constant return by value
// Result cannot be used as an lvalue

class X {
  int i;
public:
  X(int I = 0) { i = I; }
  void modify() { i++; }
};

X f5() {
  return X();
}

const X f6() {
  return X();
}

void f7(X& x) { // Pass by non-const reference
  x.modify();
}

int main() {
  f5() = X(1); // OK -- non-const return value
  f5().modify(); // OK
// Causes compile-time errors:
//!  f7(f5());
//!  f6() = X(1);
//!  f6().modify();
//!  f7(f6());
} ///:~