https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64970
Bug ID: 64970
Summary: Hard error instead of SFINAE for expression in nested
template alias
Product: gcc
Version: 4.9.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: eric.niebler at gmail dot com
The following code gives a hard error. I believe it should not.
template<typename T>
T && declval();
template<typename T>
struct void_ { using type = void; };
template<typename T>
using void_t = typename void_<T>::type;
template<class A, class B>
struct Outer
{
template<class C, class D>
using Inner = decltype(true ? declval<C>() : declval<D>());
};
template<class A, class B, typename Enable = void>
struct S
{};
template<class A, class B>
struct S<A, B, void_t<typename Outer<A, B>::template Inner<A, B>>>
{};
struct A{};
struct B{};
int main()
{
S<A, B> s;
}
The error:
test.cpp: In substitution of ‘template<class A, class B> template<class C,
class D> using Inner = decltype ((true ? declval<C>() : declval<D>())) [with C
= A; D = B; A = A; B = B]’:
test.cpp:32:13: required from here
test.cpp:15:33: error: no match for ternary ‘operator?:’ (operand types are
‘bool’, ‘A’, and ‘B’)
using Inner = decltype(true ? declval<C>() : declval<D>());
^
