https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110344
Anthony Lai <nylonhat at gmail dot com> changed:
What |Removed |Added
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CC| |nylonhat at gmail dot com
--- Comment #7 from Anthony Lai <nylonhat at gmail dot com> ---
(In reply to GCC Commits from comment #4)
> c++: C++26 constexpr cast from void* [PR110344]
>
> P2768 allows static_cast from void* to ob* in constant evaluation if the
> pointer does in fact point to an object of the appropriate type.
> cxx_fold_indirect_ref already does the work of finding such an object if
> it
> happens to be a subobject rather than the outermost object at that
> address,
> as in constexpr-voidptr2.C.
Currently gcc allows constexpr cast from void* for non similar types such as:
- From object to first member
- From first member to object
- From derived to base
- From base to derived
- From union to any of it's members
However it does not allow cast from union member to union. Is this intended?
union U {int member = 0;};
consteval auto test_union(){
U u{};
//union to any member allowed
void* u_void_ptr = &u;
int* int_ptr = static_cast<int*>(u_void_ptr);
//member to union not allowed
void* member_void_ptr = &u.member;
U* u_ptr = static_cast<U*>(member_void_ptr);
}
See: https://godbolt.org/z/53ohd46xv
