https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94074
Bug ID: 94074
Summary: bogus modifying a const object error with const
COMPONENT_REF
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: mpolacek at gcc dot gnu.org
Target Milestone: ---
typedef decltype (sizeof (0)) size_t;
template <typename E, size_t N>
struct array
{
constexpr const E &operator[](size_t n) const noexcept { return elems[n]; }
E elems[N];
};
template <typename T>
struct S {
using U = array<T, 4>;
U m;
constexpr S(int) : m{}
{
const_cast<int &>(const_cast<const U &>(m)[0]) = 42;
}
};
constexpr S<int> p = { 10 };
$ ./cc1plus -quiet q.C
q.C:20:27: in ‘constexpr’ expansion of ‘S<int>(10)’
q.C:16:52: error: modifying a const object ‘(int&)(&(&(const
U&)(&((S<int>*)this)->S<int>::m))->array<int, 4>::operator[](0))’ is not
allowed in a constant expression
16 | const_cast<int &>(const_cast<const U &>(m)[0]) = 42;
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~
q.C:20:27: note: originally declared ‘const’ here
20 | constexpr S<int> p = { 10 };
| ^
ISTM we shouldn't error here.
