Fib Fun

fib_lol.cpp

#include <array>
#include <utility>

using Int = unsigned long long;

template<Int N, Int A = 0x0llu, Int B = 0x1llu>
constexpr Int Fib = []() constexpr {
  if constexpr(N == 0)
    return A;
  else if constexpr(N == 1)
    return B;
  else if constexpr(N > 1)
    return Fib<N - 1, B, A + B>;
}();

// ============================================================================

template <Int N, auto...>
struct FibWrapper {
  static constexpr Int value = Fib<N>;
};

// ============================================================================

template <auto ... Vs>
struct seq;

template <typename>
struct seq_type;

template <auto V, auto ... Vs>
struct seq_type<seq<V,Vs...>> {
  using type = decltype(V);
};

template <typename T>
using seq_type_t = typename seq_type<T>::type;

template <typename> struct as_seq;
template <typename T, T ... Vs>
struct as_seq<std::integer_sequence<T,Vs...>> {
  using type = seq<Vs...>;
};

template <typename T>
using as_seq_t = typename as_seq<T>::type;

// ============================================================================

template <
  typename T,
  typename List,
  template<T, auto...> class Function,
  auto ... Args>
struct apply;

template <
  typename T,
  auto ... Args,
  template <T, auto...> class Fn,
  template <auto...> class Seq,
  T... Values>
struct apply<T, Seq<Values...>, Fn, Args...> {
  using type = Seq<(Fn<Values, Args...>::value)...>;
};

template <
  typename List,
  template <seq_type_t<List>, auto...> class Fn,
  auto ... Args>
using apply_t = typename apply<seq_type_t<List>, List, Fn, Args...>::type;

// ============================================================================

template <typename>
struct as_array;

template <template <auto...> class Seq, auto ... Vs>
struct as_array<Seq<Vs...>> {
  using Type_ = seq_type_t<Seq<Vs...>>;
  static constexpr std::array<Type_, sizeof...(Vs)> value {{ Vs... }};
};

template <typename T>
constexpr auto as_array_v = as_array<T>::value;

// ============================================================================

using Seq = as_seq_t<std::make_integer_sequence<Int, 94>>;

auto fibs = as_array_v<apply_t<Seq, FibWrapper>>;