gcc/testsuite/g++.dg/cpp0x/sfinae10.C

// PR c++/48452
// { dg-do compile { target c++11 } }
namespace std {
  template <class T> T&& declval();
}

template<class T, class... Args>
decltype(T(std::declval<Args>()...), char()) f(int);

template<class, class...>
char (&f(...))[2];

struct A { virtual ~A() = 0; };
struct B {};

static_assert(sizeof(f<A, int, int>(0)) != 1, "Error"); // a
static_assert(sizeof(f<B, void, int>(0)) != 1, "Error"); // b
static_assert(sizeof(f<void, int, int>(0)) != 1, "Error"); // c