Error(s):

source_file.cpp:11:2: error: static_assert failed "Not enough types to index"
        static_assert(always_false<Ts...>::value, "Not enough types to index");
        ^             ~~~~~~~~~~~~~~~~~~~~~~~~~~
source_file.cpp:27:16: error: ambiguous partial specializations of 'split_impl<0, std::__1::tuple<>, x<0>, x<1> >'
struct split : split_impl<I, std::tuple<>, Ts...> {};
               ^
source_file.cpp:31:1: note: in instantiation of template class 'split<0, x<0>, x<1> >' requested here
split<0, x<0>, x<1>>::rest z = nullptr;
^
source_file.cpp:15:8: note: partial specialization matches [with Ts = <>, Us = <x<0>, x<1>>]
struct split_impl<0, std::tuple<Ts...>, Us...>
       ^
source_file.cpp:22:8: note: partial specialization matches [with I = 0, Ts = <>, T = x<0>, Us = <x<1>>]
struct split_impl<I, std::tuple<Ts...>, T, Us...>
       ^
2 errors generated.