# AreAllBytesRecursiveTiedFields

template <size_t I>
struct DecayDownT : public DecayDownT<I - 1> {};

template <>
struct DecayDownT<0> {};

// -

/// Warning, AreAllBytesRecursiveTiedFields should not be used to indicate
/// the safety of a memcpy.
/// If you trust both the source and destination, you should use
/// std::is_trivially_copyable.
template <class T>
constexpr bool AreAllBytesRecursiveTiedFields(const T& t);

// -

namespace AreAllBytesRecursiveTiedFieldsImpl {

template <class T, std::enable_if_t<std::is_scalar<T>::value, bool> = true>
constexpr bool Impl(const T&, DecayDownT<3>) {
  return true;
}

template <class T, size_t N>
constexpr bool Impl(const T (&t)[N], DecayDownT<3>) {
  return AreAllBytesRecursiveTiedFields(t[0]);
}

template <class T, size_t N>
constexpr bool Impl(const std::array<T, N>& t, DecayDownT<3>) {
  return AreAllBytesRecursiveTiedFields(t[0]);
}

template <class T>
constexpr bool Impl(const Padding<T>& t, DecayDownT<3>) {
  return AreAllBytesRecursiveTiedFields(t.ignored);
}

// -

template <class T>
constexpr bool Impl(const T& t, DecayDownT<1>) {
  const auto tup = TiedFields(t);
  bool ok = AreAllBytesTiedFields(t);
  MapTuple(tup, [&](const auto& field) {
    ok &= AreAllBytesRecursiveTiedFields(field);
    return true;
  });
  return ok;
}

}  // namespace IsDenseNestedScalarsDetails

// -

template <class T>
constexpr bool AreAllBytesRecursiveTiedFields(const T& t) {
  return AreAllBytesRecursiveTiedFieldsImpl::Impl(t, DecayDownT<5>{});
}
static_assert(AreAllBytesRecursiveTiedFields(1));
// Compile error: Missing TiedFields:
// static_assert(AreAllBytesRecursiveTiedFields(std::pair<int,int>{}));