https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121521
Bug ID: 121521
Summary: elements of std::array in constexpr structured binding
is not a constant expression
Product: gcc
Version: 16.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: cooky.ykooc922 at gmail dot com
Target Milestone: ---
#include <array>
struct Point {
int x, y, z;
};
int main() {
constexpr int arr[] {1, 2, 3};
constexpr auto [a, b, c] = arr;
constexpr std::array std_arr {4, 5, 6};
constexpr auto [d, e, f] = std_arr; // error
constexpr auto [g, h, i] = std::array{42, 91, 72}; // error
constexpr auto [x, y, z] = Point {9, 0, -4};
}
>From the snippet of code above, constexpr structured bindings have no problems
with native arrays and aggregate types. But with std::array (has a member array
and uses the tuple protocol), the compiler rejects two lines:
<source>:12:32: error: '<structured bindings>.std::array<int, 3>::_M_elems[0]'
is not a constant expression
12 | constexpr auto [d, e, f] = std_arr; // error
| ^~~~~~~
<source>:12:32: error: '<structured bindings>.std::array<int, 3>::_M_elems[1]'
is not a constant expression
<source>:12:32: error: '<structured bindings>.std::array<int, 3>::_M_elems[2]'
is not a constant expression
<source>:13:53: error: '<structured bindings>.std::array<int, 3>::_M_elems[0]'
is not a constant expression
13 | constexpr auto [g, h, i] = std::array{42, 91, 72}; // error
| ^
<source>:13:53: error: '<structured bindings>.std::array<int, 3>::_M_elems[1]'
is not a constant expression
<source>:13:53: error: '<structured bindings>.std::array<int, 3>::_M_elems[2]'
is not a constant expression
