TITLE: assignment and classes with references


PROBLEM: floyd@whitelight.com (Floyd McWilliams)

Suppose I have a class Foo that contains a reference to Bar:

class Foo {
public:
  ...
  Foo & operator=(const Foo & rhs);

private:
  Bar &_bar;
  int _intVal;
};

But I can't for the life of me figure out how to write op=:


RESPONSE: clamage@Eng.Sun.COM (Steve Clamage), 19 Jan 96

You are probably thinking that you would like to redirect _bar to
refer to what rhs._bar refers to. That isn't allowed in C++. As a
consequence, a class containing reference members is likely to have
inconsistent assignment semantics. Suppose you assign different Foo objects
	f1 = f2;

Either f1._bar continues to refer to the same thing, which would violate
the equality semantics of assignment (f1==f2 would be false after the
assignment), or the thing f1._bar refers to would get the value of the
thing f2._bar refers to. That preserves the equality semantics of
assignment, but might not be appropriate for the assigment operator to do.

You might want to consider not using a reference in class Foo, or
disallowing assignment of Foo objects.