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
[Accepted as a DR at the March, 2024 meeting.]
Consider:
template<typename T> requires requires (T p[10]) { (decltype(p))nullptr; } int v = 42; auto r = v<int>; // well-formed?This example is only well-formed if the type of theparameterp is adjusted toT*, but the provisions in9.3.4.6 [dcl.fct] paragraph 5 cover function parametersonly.
One option is to specify application of the same adjustments as forfunction parameters. Another option is to specify rules that arguablyare more useful in arequires-expression.
Proposed resolution (approved by CWG 2023-11-07):
Change in 7.5.8.1 [expr.prim.req.general] paragraph 3 as follows:
Arequires-expression may introduce local parameters usingaparameter-declaration-clause(9.3.4.6 [dcl.fct]). A local parameter ofarequires-expression shall not have a default argument.The type of such a parameter is determined as specified fora function parameter in 9.3.4.6 [dcl.fct]. Theseparameters have no linkage, storage, or lifetime; they are only usedas notation for the purpose of definingrequirements. Theparameter-declaration-clause ofarequirement-parameter-list shall not terminate with anellipsis.
[Example 2:template<typename T> concept C = requires(T t, ...) { // error: terminates with an ellipsis t; }; template<typename T> concept C2 = requires(T p[2]) { (decltype(p))nullptr; // OK,p has type "pointer toT" };—end example]
CWG 2023-06-17
There are arguments in favor of both options.Forwarded to EWG withpaper issue 1582.
EWG 2023-11-07
Accept the proposed resolution and forward to CWG for inclusion in C++26.