Implement P0448R4 spanstream (#2029)

Co-authored-by: Adam Bucior <35536269+AdamBucior@users.noreply.github.com>
Co-authored-by: Charlie Barto <chbarto@microsoft.com>
Co-authored-by: Matt Stephanson <68978048+MattStephanson@users.noreply.github.com>
Co-authored-by: Stephan T. Lavavej <stl@microsoft.com>

stl/CMakeLists.txt

@@ -182,6 +182,7 @@ set(HEADERS
     ${CMAKE_CURRENT_LIST_DIR}/inc/shared_mutex
     ${CMAKE_CURRENT_LIST_DIR}/inc/source_location
     ${CMAKE_CURRENT_LIST_DIR}/inc/span
+    ${CMAKE_CURRENT_LIST_DIR}/inc/spanstream
     ${CMAKE_CURRENT_LIST_DIR}/inc/sstream
     ${CMAKE_CURRENT_LIST_DIR}/inc/stack
     ${CMAKE_CURRENT_LIST_DIR}/inc/stdatomic.h

stl/inc/__msvc_all_public_headers.hpp

@@ -115,6 +115,7 @@
 #include <scoped_allocator>
 #include <set>
 #include <span>
+#include <spanstream>
 #include <sstream>
 #include <stack>
 #include <stdexcept>

stl/inc/header-units.json

@@ -92,6 +92,7 @@
         "shared_mutex",
         "source_location",
         "span",
+        "spanstream",
         "sstream",
         "stack",
         "stdatomic.h",

stl/inc/iosfwd

@@ -189,6 +189,16 @@ template <class _Elem, class _Traits = char_traits<_Elem>, class _Alloc = alloca
 class basic_ostringstream;
 template <class _Elem, class _Traits = char_traits<_Elem>, class _Alloc = allocator<_Elem>>
 class basic_stringstream;
+#if _HAS_CXX23
+template <class _Elem, class _Traits = char_traits<_Elem>>
+class basic_spanbuf;
+template <class _Elem, class _Traits = char_traits<_Elem>>
+class basic_ispanstream;
+template <class _Elem, class _Traits = char_traits<_Elem>>
+class basic_ospanstream;
+template <class _Elem, class _Traits = char_traits<_Elem>>
+class basic_spanstream;
+#endif // _HAS_CXX23
 template <class _Elem, class _Traits = char_traits<_Elem>>
 class basic_filebuf;
 template <class _Elem, class _Traits = char_traits<_Elem>>
@@ -232,6 +242,12 @@ using fstream       = basic_fstream<char, char_traits<char>>;
 using syncbuf     = basic_syncbuf<char>;
 using osyncstream = basic_osyncstream<char>;
 #endif // _HAS_CXX20
+#if _HAS_CXX23
+using spanbuf     = basic_spanbuf<char>;
+using ispanstream = basic_ispanstream<char>;
+using ospanstream = basic_ospanstream<char>;
+using spanstream  = basic_spanstream<char>;
+#endif // _HAS_CXX23
 
 using wios           = basic_ios<wchar_t, char_traits<wchar_t>>;
 using wstreambuf     = basic_streambuf<wchar_t, char_traits<wchar_t>>;
@@ -250,6 +266,12 @@ using wfstream       = basic_fstream<wchar_t, char_traits<wchar_t>>;
 using wsyncbuf     = basic_syncbuf<wchar_t>;
 using wosyncstream = basic_osyncstream<wchar_t>;
 #endif // _HAS_CXX20
+#if _HAS_CXX23
+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 // _HAS_CXX23
 
 #if defined(_CRTBLD)
 using ushistream = basic_istream<unsigned short, char_traits<unsigned short>>;