libstdc++: Implement remaining piece of LWG 3448

Almost all of the proposed resolution for LWG 3448 is already
implemented; the only part left is to adjust the return type of
transform_view::sentinel::operator-.

libstdc++-v3/ChangeLog:

	PR libstdc++/95322
	* include/std/ranges (transform_view::sentinel::__distance_from):
	Give this a deduced return type.
	(transform_view::sentinel::operator-): Adjust the return type so
	that it's based on the constness of the iterator rather than
	that of the sentinel.
	* testsuite/std/ranges/adaptors/95322.cc: Refer to LWG 3488.

(cherry picked from commit 3ae0cd94abc15e33dc06ca7a5f76f14b1d74129f)

diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 41f35d1d1083f6e9ca5bcdcc8c3e6d08723d5dd9..98aa0d6a7c8665d7d8d1320dddf68440365255bd 100644 (file)
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -1864,7 +1864,7 @@ namespace views
          using _Base = __detail::__maybe_const_t<_Const, _Vp>;
 
          template<bool _Const2>
-           constexpr range_difference_t<_Base>
+           constexpr auto
            __distance_from(const _Iterator<_Const2>& __i) const
            { return _M_end - __i._M_current; }
 
@@ -1901,17 +1901,17 @@ namespace views
            operator==(const _Iterator<_Const2>& __x, const _Sentinel& __y)
            { return __y.__equal(__x); }
 
-         template<bool _Const2>
-           requires sized_sentinel_for<sentinel_t<_Base>,
-                      iterator_t<__detail::__maybe_const_t<_Const2, _Vp>>>
-           friend constexpr range_difference_t<_Base>
+         template<bool _Const2,
+                  typename _Base2 = __detail::__maybe_const_t<_Const2, _Vp>>
+           requires sized_sentinel_for<sentinel_t<_Base>, iterator_t<_Base2>>
+           friend constexpr range_difference_t<_Base2>
            operator-(const _Iterator<_Const2>& __x, const _Sentinel& __y)
            { return -__y.__distance_from(__x); }
 
-         template<bool _Const2>
-           requires sized_sentinel_for<sentinel_t<_Base>,
-                      iterator_t<__detail::__maybe_const_t<_Const2, _Vp>>>
-           friend constexpr range_difference_t<_Base>
+         template<bool _Const2,
+                  typename _Base2 = __detail::__maybe_const_t<_Const2, _Vp>>
+           requires sized_sentinel_for<sentinel_t<_Base>, iterator_t<_Base2>>
+           friend constexpr range_difference_t<_Base2>
            operator-(const _Sentinel& __y, const _Iterator<_Const2>& __x)
            { return __y.__distance_from(__x); }
 

diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/95322.cc b/libstdc++-v3/testsuite/std/ranges/adaptors/95322.cc
index 9279d5520a870b85ebfca8371975bcacb8038959..67bc7d33917bac840fb54c06c9718d61d49ef003 100644 (file)
--- a/libstdc++-v3/testsuite/std/ranges/adaptors/95322.cc
+++ b/libstdc++-v3/testsuite/std/ranges/adaptors/95322.cc
@@ -26,7 +26,7 @@ using __gnu_test::test_forward_range;
 void
 test01()
 {
-  // PR libstdc++/95322
+  // PR libstdc++/95322 and LWG 3488
   int a[2]{1, 2};
   test_forward_range<int> v{a};
   auto view1 = v | std::views::take(2);