[gcc r12-4615] libstdc++: Implement P2432R1 changes for views::istream

[Patrick Palka <ppalka@gcc.gnu.org>]

https://gcc.gnu.org/g:48154969d4b2e530af68ae9cd4277facf9d3f1a2

commit r12-4615-g48154969d4b2e530af68ae9cd4277facf9d3f1a2
Author: Patrick Palka <ppalka@redhat.com>
Date:   Thu Oct 21 11:55:19 2021 -0400

    libstdc++: Implement P2432R1 changes for views::istream
    
    libstdc++-v3/ChangeLog:
    
            * include/std/ranges (istream_view): Replace this function
            template with an alias template as per P2432R1.
            (wistream_view): Define as per P2432R1.
            (views::_Istream, views::istream): Likewise.
            * testsuite/std/ranges/istream_view.cc (test07): New test.

Diff:
---
 libstdc++-v3/include/std/ranges                   | 25 +++++++++++++++++++----
 libstdc++-v3/testsuite/std/ranges/istream_view.cc | 13 ++++++++++++
 2 files changed, 34 insertions(+), 4 deletions(-)

diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index d6bb78c09f9..7521cd675b3 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -782,10 +782,27 @@ namespace views
       friend _Iterator;
     };
 
-  template<typename _Val, typename _CharT, typename _Traits>
-    basic_istream_view<_Val, _CharT, _Traits>
-    istream_view(basic_istream<_CharT, _Traits>& __s)
-    { return basic_istream_view<_Val, _CharT, _Traits>{__s}; }
+  template<typename _Val>
+    using istream_view = basic_istream_view<_Val, char>;
+
+  template<typename _Val>
+    using wistream_view = basic_istream_view<_Val, wchar_t>;
+
+namespace views
+{
+  template<typename _Tp>
+    struct _Istream
+    {
+      template<typename _CharT, typename _Traits>
+	[[nodiscard]]
+	constexpr auto
+	operator()(basic_istream<_CharT, _Traits>& __e) const
+	{ return basic_istream_view<_Tp, _CharT, _Traits>(__e); }
+    };
+
+  template<typename _Tp>
+    inline constexpr _Istream<_Tp> istream;
+}
 
   // C++20 24.7 [range.adaptors] Range adaptors
 
diff --git a/libstdc++-v3/testsuite/std/ranges/istream_view.cc b/libstdc++-v3/testsuite/std/ranges/istream_view.cc
index f5c0c2a6bb0..ea7c5a35ef7 100644
--- a/libstdc++-v3/testsuite/std/ranges/istream_view.cc
+++ b/libstdc++-v3/testsuite/std/ranges/istream_view.cc
@@ -103,6 +103,18 @@ test06()
   static_assert( std::is_same_v<V, W> );
 }
 
+void
+test07()
+{
+  // P2432R1, views::istream
+  auto nums = std::istringstream("0 1 2 3 4");
+  ranges::istream_view<int> v(nums);
+  int sum = 0;
+  for (int val : views::istream<int>(nums))
+    sum += val;
+  VERIFY( sum == 10 );
+}
+
 int
 main()
 {
@@ -112,4 +124,5 @@ main()
   test04();
   test05();
   test06();
+  test07();
 }