1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
|
// 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!");
|
