https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64169
Bug ID: 64169
Summary: Partial template specialization of reference-qualified
operator templates
Product: gcc
Version: 4.9.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: knoepfel at fnal dot gov
System : x86_64-apple-darwin13.4.0
options: -Wall -Wextra
std : c++1y
The preprocessed version of the below code looks identical except for the
#include <iostream> contents.
Consider the following code where I attempt to specialize the &-qualified
version of operator <<.
BEGIN_CODE
namespace {
template <typename T>
class A {
public:
template < typename U> A&& operator << ( U const & ) && {
std::cerr << "... && version\n";
return std::move(*this);
}
template <typename U> A& operator << ( U const &) & {
std::cerr << "... & version\n";
return *this;
}
};
template<>
template<typename U>
A<int>& A<int>::operator<< ( U const & ) & {
std::cerr << "... & version (int)\n";
return *this;
}
}
int main() {
A<double>() << "";
A<double> adouble;
adouble << "";
A<int>() << "";
A<int> aint;
aint << "";
}
END_CODE
The gcc compile errors are:
ref-qualified-operators.cpp:25:11: error: ambiguous template specialization
‘operator<< <>’ for ‘{anonymous}::A<int>& {anonymous}::A<int>::operator<<(const
U&) &’
A<int>& A<int>::operator<< ( U const & ) & {
^
ref-qualified-operators.cpp:10:32: note: candidates are: template<class U>
{anonymous}::A<T>&& {anonymous}::A<T>::operator<<(const U&) && [with U = U; T =
int]
template < typename U> A&& operator << ( U const & ) && {
^
ref-qualified-operators.cpp:15:30: note: template<class U>
{anonymous}::A<T>& {anonymous}::A<T>::operator<<(const U&) & [with U = U; T =
int]
template <typename U> A& operator << ( U const &) & {
^
The above code is accepted by clang 3.5 and outputs:
... && version
... & version
... && version
... & version (int)
