https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100465
--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Reduced:
namespace N
{
template<typename C>
struct string_view
{
using char_type = C;
};
template<typename C>
struct string
{
void operator+=(const string&);
template<typename T, typename = typename T::char_type>
void operator+=(const T&);
};
template<typename T>
void f()
{
string<T> s;
s += string_view<T>();
}
} // namespace N
template<typename T1, typename T2>
void operator+=(T1&, const T2&){}
int main()
{
N::f<char>();
}
Clang and EDG compile this, GCC doesn't:
100465.cc: In instantiation of ‘void N::f() [with T = char]’:
100465.cc:32:14: required from here
100465.cc:22:5: error: ambiguous overload for ‘operator+=’ (operand types are
‘N::string<char>’ and ‘N::string_view<char>’)
22 | s += string_view<T>();
| ~~^~~~~~~~~~~~~~~~~~~
100465.cc:15:8: note: candidate: ‘void N::string<C>::operator+=(const T&) [with
T = N::string_view<char>; <template-parameter-2-2> = char; C = char]’
15 | void operator+=(const T&);
| ^~~~~~~~
100465.cc:28:6: note: candidate: ‘void operator+=(T1&, const T2&) [with T1 =
N::string<char>; T2 = N::string_view<char>]’
28 | void operator+=(T1&, const T2&){}
| ^~~~~~~~
