https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80544
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
And also reinterpret_cast:
template<typename T> struct check { };
template<typename T> struct check<const T>;
template<typename T> check<T> f(T&&) { return {}; }
template<typename T> T val() { return {}; }
int main() {
int i;
f(static_cast<int* const>(&i));
f(const_cast<int* const>(&i));
f(reinterpret_cast<long* const>(&i));
}
v.cc: In function ‘int main()’:
v.cc:10:32: error: invalid use of incomplete type ‘struct check<int* const>’
f(static_cast<int* const>(&i));
^
v.cc:1:29: note: declaration of ‘struct check<int* const>’
template<typename T> struct check { };
^~~~~
v.cc:11:31: error: invalid use of incomplete type ‘struct check<int* const>’
f(const_cast<int* const>(&i));
^
v.cc:1:29: note: declaration of ‘struct check<int* const>’
template<typename T> struct check { };
^~~~~
v.cc:12:38: error: invalid use of incomplete type ‘struct check<long int*
const>’
f(reinterpret_cast<long* const>(&i));
^
v.cc:1:29: note: declaration of ‘struct check<long int* const>’
template<typename T> struct check { };
^~~~~
v.cc: In instantiation of ‘check<T> f(T&&) [with T = int* const]’:
v.cc:10:32: required from here
v.cc:4:31: error: return type ‘struct check<int* const>’ is incomplete
template<typename T> check<T> f(T&&) { return {}; }
^
v.cc: In instantiation of ‘check<T> f(T&&) [with T = long int* const]’:
v.cc:12:38: required from here
v.cc:4:31: error: return type ‘struct check<long int* const>’ is incomplete
