Viewing file:  sfinae3.C (1.39 KB) -rw-r--r--
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// { dg-do compile { target c++11 } }
namespace std { template <class T> T&& declval(); }
template<typename _Tp, typename... _Args>
class is_constructible_mini
{
typedef char __one;
typedef struct { char __arr[2]; } __two;
template<typename _Tp1, typename... _Args1>
static decltype(::new _Tp1(std::declval<_Args1>()...), __one())
__test(int);
template<typename, typename...>
static __two __test(...);
public:
static const bool value = sizeof(__test<_Tp, _Args...>(0)) == 1;
};
/*
template<typename _Tp>
class is_constructible_mini<_Tp>
{
typedef char __one;
typedef struct { char __arr[2]; } __two;
template<typename _Tp1>
static decltype(::new _Tp1, __one()) __test(int);
template<typename>
static __two __test(...);
public:
static const bool value
= sizeof(__test<typename std::remove_cv<_Tp>::type>(0)) == 1;
};
*/
struct A
{
A(int);
};
struct B { };
static_assert( is_constructible_mini<A, int>::value, "");
static_assert( is_constructible_mini<A, A>::value, "");
static_assert( !is_constructible_mini<A, int, double>::value, "");
static_assert( !is_constructible_mini<A>::value, ""); // doesn't compile without the
// partial specialization
static_assert( is_constructible_mini<B>::value, "");
static_assert( is_constructible_mini<const B>::value, "");
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