0
如果为0
,则按预期工作(从列表中获取索引类型)。如果1 static_assert()
总是跳闸。我会认为static_assert()
只会发生在所有的typename
都用完了。为什么不是这样?为什么`static_assert`总是被调用?
#define USE_STATIC_ASSERT 1
template <unsigned int I, typename ...Ts>
struct items;
template <typename T, typename ...Ts>
struct items<0, T, Ts...>
{
typedef T type;
};
template <unsigned int I, typename T, typename ...Ts>
struct items<I, T, Ts...> : items<I-1, Ts...>
{
};
#if USE_STATIC_ASSERT
template <unsigned int I>
struct items<I>
{
static_assert(false, "Ran out of Ts.");
};
#endif
int main()
{
cout << is_same<float, items<1, int, float, double>::type>::value << endl;
}