https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118302
Bug ID: 118302
Summary: Invalid 'static_cast' from derived type to private
based type is not rejected during in-class
initialization of static const member of template
class
Product: gcc
Version: 15.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: wangbopku15 at gmail dot com
Target Milestone: ---
GCC generates no error for the invalid 'static_cast' statement in the following
test:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
struct Base {};
struct Derived : private Base {};
template <typename T> struct A {
static const int N = sizeof(static_cast<Base>(Derived()));
};
int main(){
A<int> aa;
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
As a comparison, clang rejects it with:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
<source>:6:53: error: cannot cast 'Derived' to its private base class 'Base'
6 | static const int N = sizeof(static_cast<Base>(Derived()));
| ^
<source>:3:18: note: declared private here
3 | struct Derived : private Base {};
| ^~~~~~~~~~~~
<source>:6:53: error: cannot cast 'Derived' to its private base class 'Base'
6 | static const int N = sizeof(static_cast<Base>(Derived()));
| ^
<source>:10:16: note: in instantiation of template class 'A<int>' requested
here
10 | A<int> aa;
| ^
<source>:3:18: note: declared private here
3 | struct Derived : private Base {};
| ^~~~~~~~~~~~
2 errors generated.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
MSVC with:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
<source>(6): error C2243: 'type cast': conversion from 'Derived *' to 'Base &&'
exists, but is inaccessible
<source>(6): note: the template instantiation context (the oldest one first) is
<source>(10): note: see reference to class template instantiation 'A<int>'
being compiled
Compiler returned: 2
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Note that the code can be correctly rejected if 'A' is not a template class.
https://godbolt.org/z/6hdMsod6P
