--- /dev/null
+// PR c++/66387
+// { dg-do compile { target c++14 } }
+
+namespace boost {
+namespace hana {
+namespace detail {
+namespace std {
+using size_t = decltype(0);
+}
+}
+namespace ic_detail {
+template <typename T, T> struct _with_index {
+ template <typename F> constexpr void operator()(F &&) const;
+};
+template <typename T, T v> struct _times { _with_index<T, v> with_index; };
+}
+template <typename T, T v> struct _integral_constant {
+ using value_type = T;
+ operator value_type() const;
+ ic_detail::_times<T, v> times;
+};
+template <detail::std::size_t i>
+constexpr _integral_constant<detail::std::size_t, i> size_t{};
+template <typename, typename = void> struct datatype;
+}
+}
+namespace std {
+typedef int size_t;
+inline namespace __cxx11 {}
+}
+namespace boost {
+namespace hana {
+template <bool> struct when;
+template <typename, typename, typename> struct to_impl;
+template <typename T, typename> struct datatype : datatype<T, when<true>> {};
+template <typename T, bool condition> struct datatype<T, when<condition>> {
+ using type = typename T::hana::datatype;
+};
+template <typename> struct _models;
+template <typename To, typename From>
+ struct to_impl < To,
+ From, when < _models<From> {
+} >> ;
+namespace detail {
+namespace std {
+template <typename T, T> struct integer_sequence;
+template <size_t... n> using index_sequence = integer_sequence<size_t, n...>;
+namespace int_seq_detail {
+template <size_t> struct make_index_sequence {
+ using type = index_sequence<0>;
+};
+template <typename, typename> struct cast_to;
+template <typename T, typename U, U... u>
+struct cast_to<T, integer_sequence<U, u...>> {
+ using type = integer_sequence<T, u...>;
+};
+}
+template <typename T, T>
+using make_integer_sequence = typename int_seq_detail::cast_to<
+ T, int_seq_detail::make_index_sequence<1>::type>::type;
+}
+}
+namespace ic_detail {
+template <typename T, T N, typename = detail::std::make_integer_sequence<T, N>>
+struct go;
+template <typename T, T N, T... i>
+struct go<T, N, detail::std::integer_sequence<T, i...>> {
+ using swallow = T;
+ template <typename F> static void with_index(F f) {
+ swallow{(f(_integral_constant<T, i>{}), 0)...};
+ }
+};
+template <typename T, T v>
+template <typename F>
+constexpr void _with_index<T, v>::operator()(F &&f) const {
+ go<T, 0>::with_index(f);
+}
+}
+}
+}
+namespace std {
+template <typename> class allocator;
+template <class> struct char_traits;
+template <typename _CharT, typename = char_traits<_CharT>> class basic_ostream;
+namespace __cxx11 {
+template <typename _CharT, typename = char_traits<_CharT>,
+ typename = allocator<_CharT>>
+class basic_stringstream;
+}
+typedef basic_ostream<char> ostream;
+typedef basic_stringstream<char> stringstream;
+template <typename, typename> class basic_ostream {};
+template <typename _CharT, typename>
+class basic_iostream : public basic_ostream<_CharT> {};
+namespace __cxx11 {
+template <typename _CharT, typename _Traits, typename>
+class basic_stringstream : public basic_iostream<_CharT, _Traits> {};
+}
+}
+namespace hana = boost::hana;
+template <typename> struct print_impl;
+template <typename X> void print(std::ostream os, X x) {
+ using Tag = typename hana::datatype<X>::type;
+ print_impl<Tag>::apply(os, x);
+}
+struct Vector;
+template <typename, typename> struct vector2 {
+ struct hana {
+ using datatype = Vector;
+ };
+ static constexpr std::size_t size = 0;
+};
+template <> struct print_impl<Vector> {
+ template <typename vectorN> static void apply(std::ostream, vectorN) {
+ constexpr auto N = hana::size_t<vectorN::size>;
+ N.times.with_index([&](auto) { N - hana::size_t<1>; });
+ }
+};
+int main() {
+ std::stringstream ss;
+ vector2<int, char> v2;
+ print(ss, v2);
+}