How to initialize const circular reference members

Question

For example, I have two classes

class Foo;
class Bar;

class Foo {
  const Bar &m_bar;
  ...
};

class Bar {
  const Foo &m_foo;
  ...
};

Let foo is object of Foo and bar is object of Bar. Is there any way (normal or "hacking") to create/initialize foo and bar that their members m_bar and m_foo would referenced to each other (I mean foo.m_bar is bar and bar.m_foo is 'foo')?

It is allowed to add any members to Foo and Bar, to add parents for them, to make they templates and so on.

Answer 1

What is the linkage of foo and bar? If they have external linkage, you can write something like:

extern Foo foo;
extern Bar bar;

Foo foo( bar );
Bar bar( foo );

(I'm assuming here that it is the constructors which set the reference to a parameter.)

This supposes namespace scope and static lifetime, of course (but an anonymous namespace is fine).

If they are class members, there's no problem either:

class Together
{
    Foo foo;
    Bar bar;
public:
    Together() : foo( bar ), bar( foo ) {}
};

If they're local variables (no binding), I don't think there's a solution.

EDIT:

Actually, the local variables have a simple solution: just define a local class which has them as members, and use it.