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

2024-11-11

2226. Xvalues vs lvalues in conditional expressions

[Accepted as a DR at the March, 2018 (Jacksonville) meeting.]

In the following example,

   const T a;
   T b;
   false ? a : std::move(b);

the most appropriate result would seem to be that the expression is an lvalue of type const T that refers to either a or b. However, because 7.6.16 [expr.cond] bullet 4.1 requires that the conversion bind directly to an lvalue, while std::move(b) is an xvalue, the result is a const T temporary copy-initialized from std::move(b).

Proposed resolution (November, 2017)

Change 7.6.16 [expr.cond] bullet 4.1 as follows:

Attempts are made to form an implicit conversion sequence from an operand expression E1 of type T1 to a target type related to the type T2 of the operand expression E2 as follows:

• If E2 is an lvalue, the target type is “lvalue reference to T2”, subject to the constraint that in the conversion the reference must bind directly (9.4.4 [dcl.init.ref]) to an lvalue a glvalue.

• ...