https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80544
Bug ID: 80544
Summary: result of const_cast<T* cv> should by cv-unqualified
Product: gcc
Version: 8.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: redi at gcc dot gnu.org
Target Milestone: ---
This is valid:
template<typename T> struct check { };
template<typename T> struct check<const T>; // incomplete
template<typename T> check<T> f(T&&) { return {}; }
int main() {
int i;
f(const_cast<int* const>(&i));
}
Clang accepts it, EDG accepts with a helpful warning:
"v.cc", line 8: warning: type qualifier is meaningless on cast type
f(const_cast<int* const>(&i));
^
G++ gives a bogus error:
v.cc: In function ‘int main()’:
v.cc:8:31: 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: In instantiation of ‘check<T> f(T&&) [with T = int* const]’:
v.cc:8:31: required from here
v.cc:4:31: error: return type ‘struct check<int* const>’ is incomplete
template<typename T> check<T> f(T&&) { return {}; }
^
The result of a const_cast to a pointer type is a prvalue, and since a pointer
is not a class or array type the type of the prvalue should be cv-unqualified.
