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* [Bug c++/102258] New: dynamic_cast to derived type fails during constant evaluation
@ 2021-09-09 14:31 johelegp at gmail dot com
2021-09-09 17:09 ` [Bug c++/102258] " johelegp at gmail dot com
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: johelegp at gmail dot com @ 2021-09-09 14:31 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102258
Bug ID: 102258
Summary: dynamic_cast to derived type fails during constant
evaluation
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Keywords: rejects-valid
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: johelegp at gmail dot com
CC: johelegp at gmail dot com
Target Milestone: ---
See https://godbolt.org/z/dsEzaxW47.
```C++
struct B { virtual ~B() = default; };
struct D : B { constexpr ~D() override { } };
int main() {
[]() consteval {
B* b = new D;
dynamic_cast<D&>(*b);
delete b;
}();
}
```
```
<source>: In function 'int main()':
<source>:8:4: in 'constexpr' expansion of '<lambda closure
object>main()::<lambda()>().main()::<lambda()>()'
<source>:6:5: error: reference 'dynamic_cast' failed
6 | dynamic_cast<D&>(*b);
| ^~~~~~~~~~~~~~~~~~~~
<source>:6:5: note: dynamic type 'D [1]' of its operand does not have a base
class of type 'D'
Compiler returned: 1
```
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c++/102258] dynamic_cast to derived type fails during constant evaluation
2021-09-09 14:31 [Bug c++/102258] New: dynamic_cast to derived type fails during constant evaluation johelegp at gmail dot com
@ 2021-09-09 17:09 ` johelegp at gmail dot com
2021-09-09 19:40 ` johelegp at gmail dot com
2022-10-22 22:42 ` pinskia at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: johelegp at gmail dot com @ 2021-09-09 17:09 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102258
--- Comment #1 from Johel Ernesto Guerrero Peña <johelegp at gmail dot com> ---
Workaround for my use-case: https://godbolt.org/z/5Woe8dvan.
```C++
#include <cassert>
#include <concepts>
#include <type_traits>
#include <typeinfo>
#include <utility>
struct B { virtual ~B() = default; };
struct D : B { int x{1}; constexpr ~D() override { } };
template<class DerivedPointer, class Base>
requires(
std::is_pointer_v<DerivedPointer> and
not std::is_same_v<std::remove_cv_t<std::remove_pointer_t<DerivedPointer>>,
std::remove_cv_t<Base>> and
std::derived_from<std::remove_pointer_t<DerivedPointer>, Base>)
[[nodiscard]] constexpr auto dynamic_downcast(Base* b)
-> decltype(&dynamic_cast<std::remove_pointer_t<DerivedPointer>&>(*b)) {
if (b == nullptr) return nullptr;
if (&typeid(*b) == &typeid(std::remove_pointer_t<DerivedPointer>&))
return &static_cast<std::remove_pointer_t<DerivedPointer>&>(*b);
throw std::bad_cast{};
}
int main() {
[]() consteval {
B* b = new D;
assert(dynamic_downcast<D*>(b)->x == 1);
delete b;
}();
}
```
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c++/102258] dynamic_cast to derived type fails during constant evaluation
2021-09-09 14:31 [Bug c++/102258] New: dynamic_cast to derived type fails during constant evaluation johelegp at gmail dot com
2021-09-09 17:09 ` [Bug c++/102258] " johelegp at gmail dot com
@ 2021-09-09 19:40 ` johelegp at gmail dot com
2022-10-22 22:42 ` pinskia at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: johelegp at gmail dot com @ 2021-09-09 19:40 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102258
--- Comment #2 from Johel Ernesto Guerrero Peña <johelegp at gmail dot com> ---
That still doesn't work because you can't compare (the addresses of) different
`std::type_info` objects.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug c++/102258] dynamic_cast to derived type fails during constant evaluation
2021-09-09 14:31 [Bug c++/102258] New: dynamic_cast to derived type fails during constant evaluation johelegp at gmail dot com
2021-09-09 17:09 ` [Bug c++/102258] " johelegp at gmail dot com
2021-09-09 19:40 ` johelegp at gmail dot com
@ 2022-10-22 22:42 ` pinskia at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: pinskia at gcc dot gnu.org @ 2022-10-22 22:42 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102258
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
See Also| |https://gcc.gnu.org/bugzill
| |a/show_bug.cgi?id=106107
Ever confirmed|0 |1
Status|UNCONFIRMED |NEW
Last reconfirmed| |2022-10-22
--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed.
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2022-10-22 22:42 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2021-09-09 14:31 [Bug c++/102258] New: dynamic_cast to derived type fails during constant evaluation johelegp at gmail dot com
2021-09-09 17:09 ` [Bug c++/102258] " johelegp at gmail dot com
2021-09-09 19:40 ` johelegp at gmail dot com
2022-10-22 22:42 ` pinskia at gcc dot gnu.org
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