Re: [boost] [config] A question about BOOST_NO_NESTED_FRIENDSHIP

Subject: Re: [boost] [config] A question about BOOST_NO_NESTED_FRIENDSHIP
From: John Maddock (john_at_[hidden])
Date: 2009-03-26 15:13:55

> I've been merging my recent additions to the release branch and came
> across the BOOST_NO_NESTED_FRIENDSHIP macro, which hasn't been merged.
> Looking at its description and test, I'm not certain whether this macro
> actually flags a compiler deficiency, rather than valid behavior. Here's
> the description:
>
>   If the compiler fails to support access to private members
>   from nested classes
>
> And the test:
>
>   class A {
>      static int b;
>      class B {
>         int f() { return b; }
>      };
>   };
>
> To my understanding, 11.8 says that it shouldn't compile, as B doesn't
> have any privileged access to A::b. Am I missing something?

It was changed in TC1, and the current draft says:

11.8 Nested classes [class.access.nest]
1 A nested class is a member and as such has the same access rights as any 
other member. The members of
an enclosing class have no special access to members of a nested class; the 
usual access rules (Clause 11)
shall be obeyed. [ Example:
class E {
int x;
class B { };
class I {
B b; // OK: E::I can access E::B
int y;
void f(E* p, int i) {
p->x = i; // OK: E::I can access E::x
}
};
int g(I* p) {
return p->y; // error: I::y is private
}
};
-end example ]

However, I note that nothing making use of this macro (Borland and Codegear 
compilers define it), so I don't know what the rationale was for adding it, 
and annoyingly I can't find the Trac ticket or email that requested it now 
:-((

John.