https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110216
Bug ID: 110216
Summary: Outdated implementation of tuple_size requirements for
structured binding
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: gnaggnoyil at gmail dot com
Target Milestone: ---
The following code is rejected with `g++ -std=c++20` as of GCC 13.1:
#include <tuple>
struct A { int x; };
namespace std
{
template<>
struct tuple_size<::A> {};
}
auto [x] = A{};
Clang 16.0 on the other hand accepts this code with `-std=c++20` flag.
Wording of N4849 (and also the latest working draft as of today) specifies the
expected behavior in [dcl.struct.bind]#4 as follows:
Otherwise, if the qualified-id std::tuple_size<E> names a complete class
type with a member named value, ...
Therefore, the above code shouldn't follow the requirements specified in
[dcl.struct.bind]#4 as tuple-like types. Instead, it should follow those in
[dcl.struct.bind]#5 and do the binding to data members.
This behavior change was introduced by CWG 2386 and corresponding wording
change can be found at
https://github.com/cplusplus/draft/commit/498092ced200140801180dcc9c2878a49350f946
