--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libcxx/include/experimental/iterator	Thu Feb 13 15:10:13 2020 +0900
@@ -0,0 +1,113 @@
+// -*- C++ -*-
+//===----------------------------- iterator -------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP_EXPERIMENTAL_ITERATOR
+#define _LIBCPP_EXPERIMENTAL_ITERATOR
+
+/*
+namespace std {
+  namespace experimental {
+    inline namespace fundamentals_v2 {
+
+    template <class DelimT, class charT = char, class traits = char_traits<charT>>
+        class ostream_joiner {
+        public:
+         typedef charT                        char_type;
+         typedef traits                       traits_type;
+         typedef basic_ostream<charT, traits> ostream_type;
+         typedef output_iterator_tag          iterator_category;
+         typedef void                         value_type;
+         typedef void                         difference_type;
+         typedef void                         pointer;
+         typedef void                         reference;
+
+         ostream_joiner(ostream_type& s, const DelimT& delimiter);
+         ostream_joiner(ostream_type& s, DelimT&& delimiter);
+
+         template<typename T>
+         ostream_joiner& operator=(const T& value);
+
+         ostream_joiner& operator*() noexcept;
+         ostream_joiner& operator++() noexcept;
+         ostream_joiner& operator++(int) noexcept;
+   private:
+      ostream_type* out_stream;   // exposition only
+      DelimT delim;               // exposition only
+      bool first_element;         // exposition only
+   };
+
+  template <class charT, class traits, class DelimT>
+    ostream_joiner<decay_t<DelimT>, charT, traits>
+    make_ostream_joiner(basic_ostream<charT, traits>& os, DelimT&& delimiter);
+
+    } // inline namespace fundamentals_v2
+  } // namespace experimental
+} // namespace std
+
+*/
+
+#include <experimental/__config>
+
+#if _LIBCPP_STD_VER > 11
+
+#include <iterator>
+
+_LIBCPP_BEGIN_NAMESPACE_LFTS
+
+template <class _Delim, class _CharT = char, class _Traits = char_traits<_CharT>>
+class ostream_joiner {
+public:
+
+    typedef _CharT                               char_type;
+    typedef _Traits                              traits_type;
+    typedef basic_ostream<char_type,traits_type> ostream_type;
+    typedef output_iterator_tag                  iterator_category;
+    typedef void                                 value_type;
+    typedef void                                 difference_type;
+    typedef void                                 pointer;
+    typedef void                                 reference;
+
+    ostream_joiner(ostream_type& __os, _Delim&& __d)
+        : __output_iter(_VSTD::addressof(__os)), __delim(_VSTD::move(__d)), __first(true) {}
+
+    ostream_joiner(ostream_type& __os, const _Delim& __d)
+        : __output_iter(_VSTD::addressof(__os)), __delim(__d), __first(true) {}
+
+
+    template<typename _Tp>
+    ostream_joiner& operator=(const _Tp& __v)
+    {
+        if (!__first)
+            *__output_iter << __delim;
+        __first = false;
+        *__output_iter << __v;
+        return *this;
+    }
+
+    ostream_joiner& operator*()     _NOEXCEPT { return *this; }
+    ostream_joiner& operator++()    _NOEXCEPT { return *this; }
+    ostream_joiner& operator++(int) _NOEXCEPT { return *this; }
+
+private:
+    ostream_type*   __output_iter;
+    _Delim          __delim;
+    bool            __first;
+};
+
+
+template <class _CharT, class _Traits, class _Delim>
+ostream_joiner<typename decay<_Delim>::type, _CharT, _Traits>
+make_ostream_joiner(basic_ostream<_CharT, _Traits>& __os, _Delim && __d)
+{ return ostream_joiner<typename decay<_Delim>::type, _CharT, _Traits>(__os, _VSTD::forward<_Delim>(__d)); }
+
+_LIBCPP_END_NAMESPACE_LFTS
+
+#endif /* _LIBCPP_STD_VER > 11 */
+
+#endif // _LIBCPP_EXPERIMENTAL_ITERATOR