This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 116a. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2024-12-19

850. Restrictions on use of non-static data members

[Voted into WP at October, 2009 meeting.]

The resolution of issue 613, as reflected in the sixth bullet of _N4567_.5.1.1 [expr.prim.general] paragraph 10, allows an id-expression designating a non-static data member to be used

• if... it is the sole constituent of an unevaluated operand, except for optional enclosing parentheses.

The requirement that the id-expression be the “sole constituent” of the unevaluated operand seems unnecessarily strict, forbidding such plausible use cases as

    struct S {
        int ar[42];
    };
    int i = sizeof(S::ar[0]);

or the use of the member as a function argument in template metaprogramming. The more general version of the restriction seems not to be very difficult to implement and may actually represent a simplification in some implementations.

Proposed resolution (July, 2009):

Change _N4567_.5.1.1 [expr.prim.general] paragraph 10 as follows:

• ...

• if that id-expression denotes a non-static data member and it is the sole constituent of appears in an unevaluated operand, except for optional enclosing parentheses. [Example:

    struct S {
      int m;
    };
    int i = sizeof(S::m);        // OK
    int j = sizeof(S::m + 42);   // error: reference to non-static member in subexpression OK
  

  —end example]