https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102249
Bug ID: 102249
Summary: Can't compare pointer to functions 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: ---
This is specified at https://eel.is/c++draft/expr.eq#3. See
https://godbolt.org/z/Wdradsb4a.
```C++
#include <functional>
static_assert(not std::ranges::equal_to{}([]{}, +[]{}));
static_assert(std::not_equal_to{}([]{}, +[]{}));
static_assert([]{} != +[]{});
```
```
<source>:2:15: error: non-constant condition for static assertion
2 | static_assert(not std::ranges::equal_to{}(+[]{}, +[]{}));
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from
/opt/compiler-explorer/gcc-11.2.0/include/c++/11.2.0/bits/iterator_concepts.h:37,
from
/opt/compiler-explorer/gcc-11.2.0/include/c++/11.2.0/bits/stl_iterator_base_types.h:71,
from
/opt/compiler-explorer/gcc-11.2.0/include/c++/11.2.0/bits/stl_algobase.h:65,
from
/opt/compiler-explorer/gcc-11.2.0/include/c++/11.2.0/array:40,
from
/opt/compiler-explorer/gcc-11.2.0/include/c++/11.2.0/tuple:39,
from
/opt/compiler-explorer/gcc-11.2.0/include/c++/11.2.0/functional:54,
from <source>:1:
/opt/compiler-explorer/gcc-11.2.0/include/c++/11.2.0/bits/ranges_cmp.h:93:39:
error: '(<lambda()>::_FUN == <lambda()>::_FUN)' is not a constant expression
93 | { return std::forward<_Tp>(__t) == std::forward<_Up>(__u); }
| ~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
<source>:3:34: error: non-constant condition for static assertion
3 | static_assert(std::not_equal_to{}(+[]{}, +[]{}));
| ~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~
In file included from
/opt/compiler-explorer/gcc-11.2.0/include/c++/11.2.0/functional:49,
from <source>:1:
/opt/compiler-explorer/gcc-11.2.0/include/c++/11.2.0/bits/stl_function.h:509:41:
error: '(<lambda()>::_FUN != <lambda()>::_FUN)' is not a constant expression
509 | { return std::forward<_Tp>(__t) != std::forward<_Up>(__u); }
| ~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
<source>:4:21: error: non-constant condition for static assertion
4 | static_assert(+[]{} != +[]{});
<source>:4:21: error: '(<lambda()>::_FUN != <lambda()>::_FUN)' is not a
constant expression
Compiler returned: 1
```
