https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104802
Bug ID: 104802
Summary: Non-type template parameter of reference type
disallowed under certain conditions
Product: gcc
Version: 11.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: sneves at dei dot uc.pt
Target Milestone: ---
Minimal (C++17 and 20) example:
template<auto const& ... Args>
struct S {
template<typename=void>
void operator()() const {}
};
struct weird_ {
int operator&() const { return 123; }
} const weird {};
auto f() {
S<weird> s {};
s();
}
This fails with the error:
error: '&(const weird_&)weird.weird_::operator&()' is not a valid template
argument of type 'const weird_&' because '(const
weird_&)weird.weird_::operator&()' is not a variable
Now, if either one of
- template<typename=void> is commented out, i.e., the called function is no
longer a template;
- `weird` has the `operator&` removed;
The code compiles without any issues.
As far as I can tell this example is not violating any of the constraints the
standard puts on lvalue reference parameters, and both Clang and MSVC accept
it.
