WIP - [libc++][spanstream] P0448R4: A strstream replacement using span<charT> as buffer

libcxx/docs/FeatureTestMacroTable.rst

@@ -394,7 +394,7 @@ Status
     ---------------------------------------------------------- -----------------
     ``__cpp_lib_reference_from_temporary``                     *unimplemented*
     ---------------------------------------------------------- -----------------
-    ``__cpp_lib_spanstream``                                   *unimplemented*
+    ``__cpp_lib_spanstream``                                   ``202106L``
     ---------------------------------------------------------- -----------------
     ``__cpp_lib_stacktrace``                                   *unimplemented*
     ---------------------------------------------------------- -----------------

libcxx/docs/ReleaseNotes/22.rst

@@ -39,6 +39,7 @@ Implemented Papers
 ------------------
 
 - P2321R2: ``zip`` (`Github <https://github.com/llvm/llvm-project/issues/105169>`__) (The paper is partially implemented. ``zip_transform_view`` is implemented in this release)
+- P0448R4: A ``strstream`` replacement using ``span<charT>`` as buffer (`Github <https://github.com/llvm/llvm-project/issues/105145>`__)
 
 Improvements and New Features
 -----------------------------

libcxx/docs/Status/Cxx23Papers.csv

@@ -12,7 +12,7 @@
 "`P2259R1 <https://wg21.link/P2259R1>`__","Repairing input range adaptors and counted_iterator","2021-02 (Virtual)","","",""
 "","","","","",""
 "`P0401R6 <https://wg21.link/P0401R6>`__","Providing size feedback in the Allocator interface","2021-06 (Virtual)","|Complete|","15",""
-"`P0448R4 <https://wg21.link/P0448R4>`__","A strstream replacement using span<charT> as buffer","2021-06 (Virtual)","","",""
+"`P0448R4 <https://wg21.link/P0448R4>`__","A ``strstream`` replacement using ``span<charT>`` as buffer","2021-06 (Virtual)","|Complete|","22"
 "`P1132R8 <https://wg21.link/P1132R8>`__","out_ptr - a scalable output pointer abstraction","2021-06 (Virtual)","|Complete|","19",""
 "`P1328R1 <https://wg21.link/P1328R1>`__","Making std::type_info::operator== constexpr","2021-06 (Virtual)","|Complete|","17",""
 "`P1425R4 <https://wg21.link/P1425R4>`__","Iterators pair constructors for stack and queue","2021-06 (Virtual)","|Complete|","14",""

libcxx/include/CMakeLists.txt

@@ -455,6 +455,7 @@ set(files
   __fwd/queue.h
   __fwd/set.h
   __fwd/span.h
+  __fwd/spanstream.h
   __fwd/sstream.h
   __fwd/stack.h
   __fwd/streambuf.h
@@ -1056,6 +1057,7 @@ set(files
   shared_mutex
   source_location
   span
+  spanstream
   sstream
   stack
   stdatomic.h

libcxx/include/__fwd/spanstream.h

@@ -0,0 +1,48 @@
+//===----------------------------------------------------------------------===//
+//
+// 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___FWD_SPANSTREAM_H
+#define _LIBCPP___FWD_SPANSTREAM_H
+
+#include <__config>
+#include <__fwd/string.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 23
+
+template <class _CharT, class _Traits = char_traits<_CharT>>
+class basic_spanbuf;
+template <class _CharT, class _Traits = char_traits<_CharT>>
+class basic_ispanstream;
+template <class _CharT, class _Traits = char_traits<_CharT>>
+class basic_ospanstream;
+template <class _CharT, class _Traits = char_traits<_CharT>>
+class basic_spanstream;
+
+using spanbuf     = basic_spanbuf<char>;
+using ispanstream = basic_ispanstream<char>;
+using ospanstream = basic_ospanstream<char>;
+using spanstream  = basic_spanstream<char>;
+
+#  if _LIBCPP_HAS_WIDE_CHARACTERS
+using wspanbuf     = basic_spanbuf<wchar_t>;
+using wispanstream = basic_ispanstream<wchar_t>;
+using wospanstream = basic_ospanstream<wchar_t>;
+using wspanstream  = basic_spanstream<wchar_t>;
+#  endif
+
+#endif // _LIBCPP_STD_VER >= 23
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FWD_SPANSTREAM_H

libcxx/include/iosfwd

@@ -41,6 +41,15 @@ template <class charT, class traits = char_traits<charT>, class Allocator = allo
 template <class charT, class traits = char_traits<charT>, class Allocator = allocator<charT> >
     class basic_stringstream;
 
+  template<class charT, class traits = char_traits<charT>>
+    class basic_spanbuf;                                                             // Since C++23
+  template<class charT, class traits = char_traits<charT>>
+    class basic_ispanstream;                                                         // Since C++23
+  template<class charT, class traits = char_traits<charT>>
+    class basic_ospanstream;                                                         // Since C++23
+  template<class charT, class traits = char_traits<charT>>
+    class basic_spanstream;                                                          // Since C++23
+
 template <class charT, class traits = char_traits<charT> > class basic_filebuf;
 template <class charT, class traits = char_traits<charT> > class basic_ifstream;
 template <class charT, class traits = char_traits<charT> > class basic_ofstream;
@@ -62,6 +71,11 @@ typedef basic_istringstream<char>    istringstream;
 typedef basic_ostringstream<char>    ostringstream;
 typedef basic_stringstream<char>     stringstream;
 
+using spanbuf     = basic_spanbuf<char>;                                             // Since C++23
+using ispanstream = basic_ispanstream<char>;                                         // Since C++23
+using ospanstream = basic_ospanstream<char>;                                         // Since C++23
+using spanstream  = basic_spanstream<char>;                                          // Since C++23
+
 typedef basic_filebuf<char>          filebuf;
 typedef basic_ifstream<char>         ifstream;
 typedef basic_ofstream<char>         ofstream;
@@ -77,6 +91,11 @@ typedef basic_istringstream<wchar_t> wistringstream;
 typedef basic_ostringstream<wchar_t> wostringstream;
 typedef basic_stringstream<wchar_t>  wstringstream;
 
+using wspanbuf     = basic_spanbuf<wchar_t>;                                         // Since C++23
+using wispanstream = basic_ispanstream<wchar_t>;                                     // Since C++23
+using wospanstream = basic_ospanstream<wchar_t>;                                     // Since C++23
+using wspanstream  = basic_spanstream<wchar_t>;                                      // Since C++23
+
 typedef basic_filebuf<wchar_t>       wfilebuf;
 typedef basic_ifstream<wchar_t>      wifstream;
 typedef basic_ofstream<wchar_t>      wofstream;
@@ -114,6 +133,7 @@ using wosyncstream = basic_osyncstream<wchar_t>;  // C++20
 #  include <__fwd/istream.h>
 #  include <__fwd/memory.h>
 #  include <__fwd/ostream.h>
+#  include <__fwd/spanstream.h>
 #  include <__fwd/sstream.h>
 #  include <__fwd/streambuf.h>
 #  include <__fwd/string.h>

libcxx/include/module.modulemap.in

@@ -1997,6 +1997,13 @@ module std [system] {
     export std.iterator.reverse_iterator
   }
 
+  module spanstream {
+    module fwd { header "__fwd/spanstream.h" }
+
+    header "spanstream"
+    export *
+  }
+
   module sstream {
     module fwd { header "__fwd/sstream.h" }