This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 115g. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2024-12-16

952. Insufficient description of “naming class”

[Accepted at the November, 2020 meeting as part of paper P1787R6 and moved to DR at the February, 2021 meeting.]

The access rules in 11.8.3 [class.access.base] do not appear to handle references in nested classes and outside of nonstatic member functions correctly. For example,

    struct A {
        typedef int I;    // public
    };
    struct B: private A { };
    struct C: B {
        void f() {
            I i1;         // error: access violation
        }
        I i2;             // OK
        struct D {
            I i3;         // OK
            void g() {
                I i4;     // OK
            }
        };
    };

The reason for this discrepancy is that the naming class in the reference to I is different in these cases. According to 11.8.3 [class.access.base] paragraph 5,

The access to a member is affected by the class in which the member is named. This naming class is the class in which the member name was looked up and found.

In the case of i1, the reference to I is subject to the transformation described in 11.4.3 [class.mfct.non.static] paragraph 3:

Similarly during name lookup, when an unqualified-id (7.5 [expr.prim]) used in the definition of a member function for class X resolves to a static member, an enumerator or a nested type of class X or of a base class of X, the unqualified-id is transformed into a qualified-id (7.5 [expr.prim]) in which the nested-name-specifier names the class of the member function.

As a result, the reference to I in the declaration of i1 is transformed to C::I, so that the naming class is C, and I is inacessible in C. In the remaining cases, however, the transformation does not apply. Thus, the naming class of I in these references is A, and I is publicly accessible in A.

Presumably either the definition of “naming class” must be changed or the transformation of unqualified-ids must be broadened to include all uses within the scope of a class and not just within nonstatic member functions (and following the declarator-id in the definition of a static member, per 11.4.9 [class.static] paragraph 4).