http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49225
Summary: [C++0x] Weird SFINAE behavior with variadic templates
Product: gcc
Version: 4.7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: paolo.carl...@oracle.com
I cannot understand why the below compiles, that is why the constructor isn't
disabled (whereas a static_assert in the body with the same expression would
fire if uncommented). Thanks in advance for any clarification!
//////////////////
template<typename _Tp, _Tp __v>
struct integral_constant
{
static constexpr _Tp value = __v;
typedef _Tp value_type;
typedef integral_constant<_Tp, __v> type;
constexpr operator value_type() { return value; }
};
typedef integral_constant<bool, true> true_type;
typedef integral_constant<bool, false> false_type;
template<typename _Tp, _Tp __v>
constexpr _Tp integral_constant<_Tp, __v>::value;
template<bool, typename _Tp = void>
struct enable_if
{ };
template<typename _Tp>
struct enable_if<true, _Tp>
{ typedef _Tp type; };
template<typename, typename>
struct is_same
: public false_type { };
template<typename _Tp>
struct is_same<_Tp, _Tp>
: public true_type { };
// Just bits of <type_traits> so far...
template<typename...>
struct __my_and_;
template<typename _B1>
struct __my_and_<_B1>
: public _B1
{ };
template<typename... _Args1>
struct Tt
{
template<typename... _Args2, typename = typename
enable_if<__my_and_<is_same<_Args1, _Args2>...>::value>::type>
Tt(_Args2...)
{
//static_assert(__my_and_<is_same<_Args1, _Args2>...>::value, "Error");
}
};
struct A { };
A a;
Tt<int> t(a); // The static_assert would trigger
