https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115522
Bug ID: 115522
Summary: std::to_array no longer works for struct which is
trivial but not default constructible
Product: gcc
Version: 13.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: daniel.klauer at gin dot de
Target Milestone: ---
Hi,
The following example used to compile successfully with gcc 13.2 or older, but
it no longer compiles in gcc 13.3 and 14.1:
#include <array>
#include <type_traits>
struct range {
const int min, max;
};
static_assert(std::is_trivial_v<range>);
static_assert(!std::is_default_constructible_v<range>);
static_assert(std::is_copy_constructible_v<range>);
auto my_array = std::to_array<range>({{0, 0}});
Output from g++ 13.3.0 on x86_64-pc-linux-gnu, built with
"--enable-languages=c,c++ --prefix=/opt/gcc-13.3":
$ /opt/gcc-13.3/bin/g++ -std=c++20 e.cxx -c
In file included from e.cxx:1:
/opt/gcc-13.3/include/c++/13.3.0/array: In instantiation of ‘constexpr
std::array<typename std::remove_cv< <template-parameter-1-1> >::type, _Nm>
std::to_array(_Tp (&&)[_Nm]) [with _Tp = range; long unsigned int _Nm = 1;
typename remove_cv< <template-parameter-1-1> >::type = range]’:
e.cxx:9:37: required from here
/opt/gcc-13.3/include/c++/13.3.0/array:460:44: error: use of deleted function
‘std::array<range, 1>::array()’
460 | array<remove_cv_t<_Tp>, _Nm> __arr;
| ^~~~~
/opt/gcc-13.3/include/c++/13.3.0/array:94:12: note: ‘std::array<range,
1>::array()’ is implicitly deleted because the default definition would be
ill-formed:
94 | struct array
| ^~~~~
/opt/gcc-13.3/include/c++/13.3.0/array:94:12: error: use of deleted function
‘range::range()’
e.cxx:3:8: note: ‘range::range()’ is implicitly deleted because the default
definition would be ill-formed:
3 | struct range {
| ^~~~~
e.cxx:3:8: error: uninitialized const member in ‘struct range’
e.cxx:4:15: note: ‘const int range::min’ should be initialized
4 | const int min, max;
| ^~~
e.cxx:3:8: error: uninitialized const member in ‘struct range’
3 | struct range {
| ^~~~~
e.cxx:4:20: note: ‘const int range::max’ should be initialized
4 | const int min, max;
| ^~~
/opt/gcc-13.3/include/c++/13.3.0/array:465:39: error: use of deleted function
‘range& range::operator=(const range&)’
465 | __arr._M_elems[__i] = __a[__i];
| ~~~~~~~~~~~~~~~~~~~~^~~~~~
e.cxx:3:8: note: ‘range& range::operator=(const range&)’ is implicitly deleted
because the default definition would be ill-formed:
3 | struct range {
| ^~~~~
e.cxx:3:8: error: non-static const member ‘const int range::min’, cannot use
default assignment operator
e.cxx:3:8: error: non-static const member ‘const int range::max’, cannot use
default assignment operator
It's not clear to me whether it should work in the first place, though it was
my understanding that std::to_array does not necessarily require a default
constructor, since it is closer to a move/copy operation.
