https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122269
Bug ID: 122269
Summary: Error on constexpr structured binding using tuple
protocol
Product: gcc
Version: 16.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: tkaminsk at gcc dot gnu.org
Target Milestone: ---
GCC produces error `error: '<anonymous>' is not a constant expression` when
compiling following code:
```
#include <utility>
using std::size_t;
template<size_t _Num>
struct _IndexPack
{
template<size_t _Idx>
static consteval size_t
get() noexcept
{ return _Idx; }
};
template<size_t _Num>
struct std::tuple_size<_IndexPack<_Num>>
{ static constexpr size_t value = _Num; };
template<size_t _Idx, size_t _Num>
struct std::tuple_element<_Idx, _IndexPack<_Num>>
{ using type = size_t; };
template<size_t N>
void foo()
{
constexpr auto [...ids] = _IndexPack<N>();
static_assert( sizeof...(ids) == N );
}
int main() {
foo<4>();
}
```
https://godbolt.org/z/Kvv5fxjWb
