È possibile utilizzare questo:
// the usual helpers (BTW: I wish these would be standardized!!)
template< std::size_t... Ns >
struct indices
{
typedef indices< Ns..., sizeof...(Ns) > next;
};
template< std::size_t N >
struct make_indices
{
typedef typename make_indices< N - 1 >::type::next type;
};
template<>
struct make_indices<0>
{
typedef indices<> type;
};
// and now we use them
template< typename Tuple, std::size_t N, typename T,
typename Indices = typename make_indices< std::tuple_size<Tuple>::value >::type >
struct element_replace;
template< typename... Ts, std::size_t N, typename T, std::size_t... Ns >
struct element_replace< std::tuple<Ts...>, N, T, indices<Ns...> >
{
typedef std::tuple< typename std::conditional< Ns == N, T, Ts >::type... > type;
};
e quindi utilizzarlo in questo modo:
using a_t = std::tuple<std::string,unsigned>; // start with some n-tuple
using b_t = element_replace<a_t,1,double>::type; // std::tuple<std::string,double>
using c_t = element_replace<b_t,0,char>::type; // std::tuple<char,double>
fonte
2013-03-14 14:27:42
Indici. ♥♥♥♥♥♥ – Xeo
Ho bisogno di imparare questo trucco. +1 – jrok
+1: compatto ed elegante –