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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.

2025-12-20

1472. odr-use of reference variables

[Moved to DR at the April, 2013 meeting.]

We have a special case in 6.3 [basic.def.odr] paragraph 2 thatvariables which satisfy the requirements for appearing in a constantexpression are not odr-used if the lvalue-to-rvalue conversion isimmediately applied. This special case only applies to objects, andthus does not apply to variables of reference type. Thisinconsistency seems strange, and there is implementation divergence:

  int n;  void f() {   constexpr int &r = n;   [] { return r; }; // error:r is odr-used but not captured  }

This code is accepted by g++ but rejected by clang. Shouldr beodr-used here?

Proposed resolution (October, 2012):

Change 6.3 [basic.def.odr] paragraph 3 as follows:

A variablex whose name appears as a potentially-evaluatedexpressionex isodr-used unlessxis anobject that satisfies the requirements for appearing in aconstant expression (7.7 [expr.const]) and, ifx is an object,ex is an element of the set ofpotential results of an expressione, where either thelvalue-to-rvalue conversion (7.3.2 [conv.lval]) is applied toe, ore is a discarded-value expression (Clause 7 [expr]).this is odr-used...