Viewing file:  sfinae54.C (1.03 KB) -rw-r--r--
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// PR c++/63723
// { dg-do compile { target c++11 } }
template<typename Tp> Tp declval();
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() const { return value; }
};
typedef integral_constant<bool, true> true_type;
typedef integral_constant<bool, false> false_type;
template <typename From, typename To>
class is_list_convertible_helper
{
template <typename To2>
static void requires_conversion(To2 t);
template <typename From2, typename To2,
typename = decltype(requires_conversion<To2>({declval<From2>()}))>
static true_type helper(int);
template <typename From2, typename To2>
static false_type helper(...);
public:
using type = decltype(helper<From, To>(0));
};
template <typename From, typename To>
class is_list_convertible
: public is_list_convertible_helper<From, To>::type
{ };
static_assert(!is_list_convertible<double, int>::value,
"double -> int is narrowing!");
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