Access to static protected member from friends of derived classes.

Clang Frontend
1

Hi,

A few years ago, I was trying to fix the bug 6840 [1] that relates to access to
static protected member from friends of derived classes.

I made a patch that fixes it at the time, but it was rejected because this was
considered as a drafting error in the standard [2].

Recently, I attended a talk by a Debian dev who tried to compile all debian
packages with clang. And that bug was one frequent cause of compilation error.
[3]

I was wondering if it was not time to revisit the decision, and consider that
this issue should be fixed after all.

The problem is the following:

class N { protected: static int m; };
class P : public N { friend class R; };
class R {
  int foo() {
     return N::m; // should work because the access is given via P.
    // but clang gives an error:
    // error: 'm' is a protected member of 'N'
  }
};

C++11 §11.4 explicitly states this is permitted, with an example. And gcc
supports that fine.

Opinions?

2

More a defect than a drafting error, really. I acknowledge that there's an
explicit example in the standard. I just think that the standard is mistaken
to permit this, for the reasons already enumerated and some new ones.

Notable among the new ones is that the implicit dependence on a totally
unrelated declaration would be a major burden on any serious modules
proposal.

John.

3

Is there a workaround? I have code compiling on g++ that relies upon this
behavior and I'm trying to get it to work on Clang.