This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 119a. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2026-01-08

3147. Modules, exposures: odr-use determination too simple

Section: 6.7  [basic.link]     Status: open     Submitter: Hubert Tong     Date: 2025-12-18

Consider:

  export module M;

  static int x;             // OK, TU-local
  static int &rx = x;       // OK, TU-local

  export inline int &f() {
    return rx;              // OK(!), not an odr-use
  }

The declaration of f is not an exposure because the reference to rx is not an odr-use (6.7 [basic.link] bullet 14.4), but it is impossible with current implementation technology to simulate naming x in importing translation units.

For a related example:

  export module M;

  static int x;               // OK, TU-local
  extern "C++" int &rx = x;   // OK, not an exposure (not constexpr)

  export inline int &f() {
    return rx;                // OK(!), not an odr-use
  }

In importing translation units, rx is not usable in constant expressions.

Finally:

  export module M;

  extern "C++" int x = 0;
  static int &rx = x;

  export constexpr inline int &f() {
    return rx;                // OK, not an odr-use
  }

Suggested resolution:

Change in 6.3 [basic.def.odr] paragraph 5 as follows:

A variable is named by an expression if the expression is an id-expression or splice-expression (7.5.9 [expr.prim.splice]) that designates it. A variable x that is named by a potentially-evaluated expression N that appears at a point P is odr-used by N unless