This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 117b. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.
2025-08-11
2865. Regression on result of conditional operatorSection: 7.6.16 [expr.cond] Status: DRWP Submitter: Christof Meerwald Date: 2024-01-14[Accepted as a DR at the June, 2024 meeting.]
Consider:
#include <concepts>
template <class T> T get();
template <class T>
using X = decltype(true ? get<T const&>() : get<T>());
struct C { };
static_assert(std::same_as<X<int>, int>);
static_assert(std::same_as<X<C>, C const>); // #1
Before Issue 1895, #1 was well-formed. With the reformulation based on conversion sequences, #1 is now ill-formed because both conversion sequences can be formed.
Proposed resolution (approved by CWG 2024-05-03):
Change in 7.6.16 [expr.cond] bullet 4.3 as follows:
- ...
- If E2 is a prvalue or if neither of the conversion sequences above can be formed and at least one of the operands has (possibly cv-qualified) class type:
- if T1 and T2 are the same class type (ignoring cv-qualification) :
- and if T2 is at least as cv-qualified as T1, the target type is T2,
- otherwise, no conversion sequence is formed for this operand;
- otherwise, if T2 is a base class of T1, the target type is cv1 T2, where cv1 denotes the cv-qualifiers of T1 , ;
- otherwise, the target type is the type that E2 would have after applying the lvalue-to-rvalue (7.3.2 [conv.lval]), array-to-pointer (7.3.3 [conv.array]), and function-to-pointer (7.3.4 [conv.func]) standard conversions.
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