On Tue, 11 Mar 2025, Tomasz Kaminski wrote:

> 
> 
> On Tue, Mar 11, 2025 at 5:04 PM Patrick Palka <ppa...@redhat.com> wrote:
>       On Tue, 11 Mar 2025, Tomasz Kaminski wrote:
> 
>       >
>       >
>       > On Mon, Mar 10, 2025 at 11:28 PM Patrick Palka <ppa...@redhat.com> 
> wrote:
>       >       Tested on x86_64-pc-linux-gnu, does this look OK for trunk?
>       >
>       >       -- >8 --
>       >
>       >       libstdc++-v3/ChangeLog:
>       >
>       >               * include/bits/version.def (ranges_to_input): Define.
>       >               * include/bits/version.h: Regenerate.
>       >               * include/std/ranges (ranges::to_input_view): Define 
> for C++26.
>       >               (views::__detail::__can_to_input): Likewise.
>       >               (views::_ToInput, views::to_input): Likewise.
>       >               * testsuite/std/ranges/adaptors/to_input/1.cc: New test.
>       >       ---
>       >        libstdc++-v3/include/bits/version.def         |   8 +
>       >        libstdc++-v3/include/bits/version.h           |  10 ++
>       >        libstdc++-v3/include/std/ranges               | 170 
> ++++++++++++++++++
>       >        .../std/ranges/adaptors/to_input/1.cc         |  58 ++++++
>       >        4 files changed, 246 insertions(+)
>       >        create mode 100644 
> libstdc++-v3/testsuite/std/ranges/adaptors/to_input/1.cc
>       >
>       >       diff --git a/libstdc++-v3/include/bits/version.def 
> b/libstdc++-v3/include/bits/version.def
>       >       index 2af5a54bff2..c2b5283df89 100644
>       >       --- a/libstdc++-v3/include/bits/version.def
>       >       +++ b/libstdc++-v3/include/bits/version.def
>       >       @@ -1910,6 +1910,14 @@ ftms = {
>       >          };
>       >        };
>       >
>       >       +ftms = {
>       >       +  name = ranges_to_input;
>       >       +  values = {
>       >       +    v = 202502;
>       >       +    cxxmin = 26;
>       >       +  };
>       >       +};
>       >       +
>       >        ftms = {
>       >          name = to_string;
>       >          values = {
>       >       diff --git a/libstdc++-v3/include/bits/version.h 
> b/libstdc++-v3/include/bits/version.h
>       >       index 9833023cfdc..775c8642139 100644
>       >       --- a/libstdc++-v3/include/bits/version.h
>       >       +++ b/libstdc++-v3/include/bits/version.h
>       >       @@ -2120,6 +2120,16 @@
>       >        #endif /* !defined(__cpp_lib_text_encoding) && 
> defined(__glibcxx_want_text_encoding) */
>       >        #undef __glibcxx_want_text_encoding
>       >
>       >       +#if !defined(__cpp_lib_ranges_to_input)
>       >       +# if (__cplusplus >  202302L)
>       >       +#  define __glibcxx_ranges_to_input 202502L
>       >       +#  if defined(__glibcxx_want_all) || 
> defined(__glibcxx_want_ranges_to_input)
>       >       +#   define __cpp_lib_ranges_to_input 202502L
>       >       +#  endif
>       >       +# endif
>       >       +#endif /* !defined(__cpp_lib_ranges_to_input) && 
> defined(__glibcxx_want_ranges_to_input) */
>       >       +#undef __glibcxx_want_ranges_to_input
>       >       +
>       >        #if !defined(__cpp_lib_to_string)
>       >        # if (__cplusplus >  202302L) && _GLIBCXX_HOSTED && 
> (__glibcxx_to_chars)
>       >        #  define __glibcxx_to_string 202306L
>       >       diff --git a/libstdc++-v3/include/std/ranges 
> b/libstdc++-v3/include/std/ranges
>       >       index e21f5284b46..dd97d276ef0 100644
>       >       --- a/libstdc++-v3/include/std/ranges
>       >       +++ b/libstdc++-v3/include/std/ranges
>       >       @@ -69,6 +69,7 @@
>       >        #define __glibcxx_want_ranges_slide
>       >        #define __glibcxx_want_ranges_stride
>       >        #define __glibcxx_want_ranges_to_container
>       >       +#define __glibcxx_want_ranges_to_input
>       >        #define __glibcxx_want_ranges_zip
>       >        #include <bits/version.h>
>       >
>       >       @@ -10390,6 +10391,175 @@ namespace ranges
>       >        } // namespace ranges
>       >        #endif // __cpp_lib_ranges_cache_latest
>       >
>       >       +#if __cpp_lib_ranges_to_input // C++ >= 26
>       >       +namespace ranges
>       >       +{
>       >       +  template<input_range _Vp>
>       >       +    requires view<_Vp>
>       >       +  class to_input_view : public 
> view_interface<to_input_view<_Vp>>
>       >       +  {
>       >       +    _Vp _M_base = _Vp();
>       >       +
>       >       +    template<bool _Const>
>       >       +    class _Iterator;
>       >       +
>       >       +  public:
>       >       +    to_input_view() requires default_initializable<_Vp> = 
> default;
>       >       +
>       >       +    constexpr explicit
>       >       +    to_input_view(_Vp __base)
>       >       +    : _M_base(std::move(__base))
>       >       +    { }
>       >       +
>       >       +    constexpr _Vp
>       >       +    base() const & requires copy_constructible<_Vp>
>       >       +    { return _M_base; }
>       >       +
>       >       +    constexpr _Vp
>       >       +    base() &&
>       >       +    { return std::move(_M_base); }
>       >       +
>       >       +    constexpr auto
>       >       +    begin() requires (!__detail::__simple_view<_Vp>)
>       >       +    { return _Iterator<false>(ranges::begin(_M_base)); }
>       >       +
>       >       +    constexpr auto
>       >       +    begin() const requires range<const _Vp>
>       >       +    { return _Iterator<true>(ranges::begin(_M_base)); }
>       >       +
>       >       +    constexpr auto
>       >       +    end() requires (!__detail::__simple_view<_Vp>)
>       >       +    { return ranges::end(_M_base); }
>       >       +
>       >       +    constexpr auto
>       >       +    end() const requires range<const _Vp>
>       >       +    { return ranges::end(_M_base); }
>       >       +
>       >       +    constexpr auto
>       >       +    size() requires sized_range<_Vp>
>       >       +    { return ranges::size(_M_base); }
>       >       +
>       >       +    constexpr auto
>       >       +    size() const requires sized_range<const _Vp>
>       >       +    { return ranges::size(_M_base); }
>       >       +  };
>       >       +
>       >       +  template<typename _Range>
>       >       +    to_input_view(_Range&&) -> 
> to_input_view<views::all_t<_Range>>;
>       >       +
>       >       +  template<input_range _Vp>
>       >       +    requires view<_Vp>
>       >       +  template<bool _Const>
>       >       +  class to_input_view<_Vp>::_Iterator
>       >       +  {
>       >       +    using _Base = __maybe_const_t<_Const, _Vp>;
>       >       +
>       >       +    iterator_t<_Base> _M_current = iterator_t<_Base>();
>       >       +
>       >       +    constexpr explicit
>       >       +    _Iterator(iterator_t<_Base> __current)
>       >       +    : _M_current(std::move(__current))
>       >       +    { }
>       >       +
>       >       +    friend to_input_view;
>       >       +    friend _Iterator<!_Const>;
>       >       +
>       >       +  public:
>       >       +    using difference_type = range_difference_t<_Base>;
>       >       +    using value_type = range_value_t<_Base>;
>       >       +    using iterator_concept = input_iterator_tag;
>       >       +
>       >       +    _Iterator() requires 
> default_initializable<iterator_t<_Base>> = default;
>       >       +
>       >       +    _Iterator(_Iterator&&) = default;
>       >       +    _Iterator& operator=(_Iterator&&) = default;
>       >       +
>       >       +    constexpr
>       >       +    _Iterator(_Iterator<!_Const> __i)
>       >       +      requires _Const && convertible_to<iterator_t<_Vp>, 
> iterator_t<_Base>>
>       >       +    : _M_current(std::move(__i._M_current))
>       >       +    { }
>       >       +
>       >       +    constexpr iterator_t<_Base>
>       >       +    base() &&
>       >       +    { return std::move(_M_current); }
>       >       +
>       >       +    constexpr const iterator_t<_Base>&
>       >       +    base() const & noexcept
>       >       +    { return _M_current; }
>       >       +
>       >       +    constexpr decltype(auto)
>       >       +    operator*() const
>       >       +    { return *_M_current; }
>       >       +
>       >       +    constexpr _Iterator&
>       >       +    operator++()
>       >       +    {
>       >       +      ++_M_current;
>       >       +      return *this;
>       >       +    }
>       >       +
>       >       +    constexpr void
>       >       +    operator++(int)
>       >       +    { ++*this; }
>       >       +
>       >       +    friend constexpr bool
>       >       +    operator==(const _Iterator& __x, const sentinel_t<_Base>& 
> __y)
>       >       +    { return __x._M_current == __y; }
>       >       +
>       >       +    friend constexpr difference_type
>       >       +    operator-(const sentinel_t<_Base>& __y, const _Iterator& 
> __x)
>       >       +      requires sized_sentinel_for<sentinel_t<_Base>, 
> iterator_t<_Base>>
>       >       +    { return __y - __x._M_current; }
>       >       +
>       >       +    friend constexpr difference_type
>       >       +    operator-(const _Iterator& __x, const sentinel_t<_Base>& 
> __y)
>       >       +      requires sized_sentinel_for<sentinel_t<_Base>, 
> iterator_t<_Base>>
>       >       +    { return __x._M_current - __y; }
>       >       +
>       >       +    friend constexpr range_rvalue_reference_t<_Base>
>       >       +    iter_move(const _Iterator& __i)
>       >       +      noexcept(noexcept(ranges::iter_move(__i._M_current)))
>       >       +    { return ranges::iter_move(__i._M_current); }
>       >       +
>       >       +    friend constexpr void
>       >       +    iter_swap(const _Iterator& __x, const _Iterator& __y)
>       >       +      noexcept(noexcept(ranges::iter_swap(__x._M_current, 
> __y._M_current)))
>       >       +      requires indirectly_swappable<iterator_t<_Base>>
>       >       +    { ranges::iter_swap(__x._M_current, __y._M_current); }
>       >       +  };
>       >       +
>       >       +  namespace views
>       >       +  {
>       >       +    namespace __detail
>       >       +    {
>       >       +      template<typename _Tp>
>       >       +       concept __can_to_input = requires { 
> to_input_view(std::declval<_Tp>()); };
>       >       +    }
>       >       +
>       >       +    struct _ToInput : __adaptor::_RangeAdaptorClosure<_ToInput>
>       >       +    {
>       >       +      template<viewable_range _Range>
>       >       +       requires __detail::__can_to_input<_Range>
>       >       +       constexpr auto
>       >       +       operator() [[nodiscard]] (_Range&& __r) const
>       >       +       {
>       >       +         if constexpr (input_range<_Range>
>       >       +                       && !common_range<_Range>
>       >       +                       && !forward_range<_Range>)
>       >       +           return views::all(__r);
>       >       +         else
>       >       +           return to_input_view(std::forward<_Range>(__r));
>       >       +       }
>       >       +
>       >       +      static constexpr bool _S_has_simple_call_op = true;
>       >       +    };
>       >       +
>       >       +    inline constexpr _ToInput to_input;
>       >       +  }
>       >       +} // namespace ranges
>       >       +#endif // __cpp_lib_ranges_to_input
>       >       +
>       >        _GLIBCXX_END_NAMESPACE_VERSION
>       >        } // namespace std
>       >        #endif // library concepts
>       >       diff --git 
> a/libstdc++-v3/testsuite/std/ranges/adaptors/to_input/1.cc 
> b/libstdc++-v3/testsuite/std/ranges/adaptors/to_input/1.cc
>       >       new file mode 100644
>       >       index 00000000000..1e43281adb4
>       >       --- /dev/null
>       >       +++ b/libstdc++-v3/testsuite/std/ranges/adaptors/to_input/1.cc
>       >       @@ -0,0 +1,58 @@
>       >       +// { dg-do run { target c++26 } }
>       >       +
>       >       +#include <ranges>
>       >       +
>       >       +#if __cpp_lib_ranges_to_input != 202502L
>       >       +# error "Feature-test macro __cpp_lib_ranges_to_input has 
> wrong value in <ranges>"
>       >       +#endif
>       >       +
>       >       +#include <algorithm>
>       >       +#include <vector>
>       >       +#include <testsuite_hooks.h>
>       >       +#include <testsuite_iterators.h>
>       >       +
>       >       +namespace ranges = std::ranges;
>       >       +namespace views = std::views;
>       >       +
>       >       +void
>       >       +test01()
>       >       +{
>       >       +  std::vector<int> r{1,2,3};
>       >       +  auto v = r | views::to_input;
>       >       +  using type = decltype(v);
>       >       +  static_assert( ranges::input_range<type> && 
> !ranges::forward_range<type> );
>       >       +
>       >       +  VERIFY( ranges::equal(v.base(), r) );
>       >       +  VERIFY( v.size() == r.size() );
>       >       +  VERIFY( v.end() == r.end() );
>       >       +  auto it = v.begin();
>       >       +  VERIFY( it != r.end() );
>       >       +  *it = 42;
>       >       +  ++it;
>       >       +  *it = 43;
>       >       +  it++;
>       >       +  ranges::iter_swap(v.begin(), it);
>       >
>       > As far as I can tell this is not invoking the iter_swap friend 
> function, and instead defaulting to swap by 3 iter_moves.
>       > We cannot copy the iterator, but you could replace v.begin(), with 
> views::to_input(v).begin() to call the overload, and
>       > have the same effect.
> 
>       v is the to_input_view, not the vector, so both arguments are
>       to_input_view iterators and I'd expect the friend function gets
>       used here?  Looks like it is, demonstrated by a static_assert(false)
>       added to its body:
> 
> Indeed, I got confused by the name (v being for vector), and the friend 
> overload is called.

The range adaptor tests tend to use 'v' as the name of the adapted view
FWIW.

> We are also calling begin on input_range twice, which is not guaranteed to 
> work in general,
> but seem to be well-defined in this case.

Hmm good point -- while the to_input_view iterator is always move-only,
it's not always single pass, the latter property is inherited from the
underlying range.

Here's an updated patch that uses std::same_as in the testcase, and
slightly extends the testcase to verify views::to_input is idempotent.
I also added a missing forward in the views::all branch of to_input.

-- >8 --

libstdc++-v3/ChangeLog:

        * include/bits/version.def (ranges_to_input): Define.
        * include/bits/version.h: Regenerate.
        * include/std/ranges (ranges::to_input_view): Define for C++26.
        (views::__detail::__can_to_input): Likewise.
        (views::_ToInput, views::to_input): Likewise.
        * testsuite/std/ranges/adaptors/to_input/1.cc: New test.
---
 libstdc++-v3/include/bits/version.def         |   8 +
 libstdc++-v3/include/bits/version.h           |  10 ++
 libstdc++-v3/include/std/ranges               | 170 ++++++++++++++++++
 .../std/ranges/adaptors/to_input/1.cc         |  59 ++++++
 4 files changed, 247 insertions(+)
 create mode 100644 libstdc++-v3/testsuite/std/ranges/adaptors/to_input/1.cc

diff --git a/libstdc++-v3/include/bits/version.def 
b/libstdc++-v3/include/bits/version.def
index 2af5a54bff2..c2b5283df89 100644
--- a/libstdc++-v3/include/bits/version.def
+++ b/libstdc++-v3/include/bits/version.def
@@ -1910,6 +1910,14 @@ ftms = {
   };
 };
 
+ftms = {
+  name = ranges_to_input;
+  values = {
+    v = 202502;
+    cxxmin = 26;
+  };
+};
+
 ftms = {
   name = to_string;
   values = {
diff --git a/libstdc++-v3/include/bits/version.h 
b/libstdc++-v3/include/bits/version.h
index 9833023cfdc..775c8642139 100644
--- a/libstdc++-v3/include/bits/version.h
+++ b/libstdc++-v3/include/bits/version.h
@@ -2120,6 +2120,16 @@
 #endif /* !defined(__cpp_lib_text_encoding) && 
defined(__glibcxx_want_text_encoding) */
 #undef __glibcxx_want_text_encoding
 
+#if !defined(__cpp_lib_ranges_to_input)
+# if (__cplusplus >  202302L)
+#  define __glibcxx_ranges_to_input 202502L
+#  if defined(__glibcxx_want_all) || defined(__glibcxx_want_ranges_to_input)
+#   define __cpp_lib_ranges_to_input 202502L
+#  endif
+# endif
+#endif /* !defined(__cpp_lib_ranges_to_input) && 
defined(__glibcxx_want_ranges_to_input) */
+#undef __glibcxx_want_ranges_to_input
+
 #if !defined(__cpp_lib_to_string)
 # if (__cplusplus >  202302L) && _GLIBCXX_HOSTED && (__glibcxx_to_chars)
 #  define __glibcxx_to_string 202306L
diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index e21f5284b46..c2a2d6f4e05 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -69,6 +69,7 @@
 #define __glibcxx_want_ranges_slide
 #define __glibcxx_want_ranges_stride
 #define __glibcxx_want_ranges_to_container
+#define __glibcxx_want_ranges_to_input
 #define __glibcxx_want_ranges_zip
 #include <bits/version.h>
 
@@ -10390,6 +10391,175 @@ namespace ranges
 } // namespace ranges
 #endif // __cpp_lib_ranges_cache_latest
 
+#if __cpp_lib_ranges_to_input // C++ >= 26
+namespace ranges
+{
+  template<input_range _Vp>
+    requires view<_Vp>
+  class to_input_view : public view_interface<to_input_view<_Vp>>
+  {
+    _Vp _M_base = _Vp();
+
+    template<bool _Const>
+    class _Iterator;
+
+  public:
+    to_input_view() requires default_initializable<_Vp> = default;
+
+    constexpr explicit
+    to_input_view(_Vp __base)
+    : _M_base(std::move(__base))
+    { }
+
+    constexpr _Vp
+    base() const & requires copy_constructible<_Vp>
+    { return _M_base; }
+
+    constexpr _Vp
+    base() &&
+    { return std::move(_M_base); }
+
+    constexpr auto
+    begin() requires (!__detail::__simple_view<_Vp>)
+    { return _Iterator<false>(ranges::begin(_M_base)); }
+
+    constexpr auto
+    begin() const requires range<const _Vp>
+    { return _Iterator<true>(ranges::begin(_M_base)); }
+
+    constexpr auto
+    end() requires (!__detail::__simple_view<_Vp>)
+    { return ranges::end(_M_base); }
+
+    constexpr auto
+    end() const requires range<const _Vp>
+    { return ranges::end(_M_base); }
+
+    constexpr auto
+    size() requires sized_range<_Vp>
+    { return ranges::size(_M_base); }
+
+    constexpr auto
+    size() const requires sized_range<const _Vp>
+    { return ranges::size(_M_base); }
+  };
+
+  template<typename _Range>
+    to_input_view(_Range&&) -> to_input_view<views::all_t<_Range>>;
+
+  template<input_range _Vp>
+    requires view<_Vp>
+  template<bool _Const>
+  class to_input_view<_Vp>::_Iterator
+  {
+    using _Base = __maybe_const_t<_Const, _Vp>;
+
+    iterator_t<_Base> _M_current = iterator_t<_Base>();
+
+    constexpr explicit
+    _Iterator(iterator_t<_Base> __current)
+    : _M_current(std::move(__current))
+    { }
+
+    friend to_input_view;
+    friend _Iterator<!_Const>;
+
+  public:
+    using difference_type = range_difference_t<_Base>;
+    using value_type = range_value_t<_Base>;
+    using iterator_concept = input_iterator_tag;
+
+    _Iterator() requires default_initializable<iterator_t<_Base>> = default;
+
+    _Iterator(_Iterator&&) = default;
+    _Iterator& operator=(_Iterator&&) = default;
+
+    constexpr
+    _Iterator(_Iterator<!_Const> __i)
+      requires _Const && convertible_to<iterator_t<_Vp>, iterator_t<_Base>>
+    : _M_current(std::move(__i._M_current))
+    { }
+
+    constexpr iterator_t<_Base>
+    base() &&
+    { return std::move(_M_current); }
+
+    constexpr const iterator_t<_Base>&
+    base() const & noexcept
+    { return _M_current; }
+
+    constexpr decltype(auto)
+    operator*() const
+    { return *_M_current; }
+
+    constexpr _Iterator&
+    operator++()
+    {
+      ++_M_current;
+      return *this;
+    }
+
+    constexpr void
+    operator++(int)
+    { ++*this; }
+
+    friend constexpr bool
+    operator==(const _Iterator& __x, const sentinel_t<_Base>& __y)
+    { return __x._M_current == __y; }
+
+    friend constexpr difference_type
+    operator-(const sentinel_t<_Base>& __y, const _Iterator& __x)
+      requires sized_sentinel_for<sentinel_t<_Base>, iterator_t<_Base>>
+    { return __y - __x._M_current; }
+
+    friend constexpr difference_type
+    operator-(const _Iterator& __x, const sentinel_t<_Base>& __y)
+      requires sized_sentinel_for<sentinel_t<_Base>, iterator_t<_Base>>
+    { return __x._M_current - __y; }
+
+    friend constexpr range_rvalue_reference_t<_Base>
+    iter_move(const _Iterator& __i)
+      noexcept(noexcept(ranges::iter_move(__i._M_current)))
+    { return ranges::iter_move(__i._M_current); }
+
+    friend constexpr void
+    iter_swap(const _Iterator& __x, const _Iterator& __y)
+      noexcept(noexcept(ranges::iter_swap(__x._M_current, __y._M_current)))
+      requires indirectly_swappable<iterator_t<_Base>>
+    { ranges::iter_swap(__x._M_current, __y._M_current); }
+  };
+
+  namespace views
+  {
+    namespace __detail
+    {
+      template<typename _Tp>
+       concept __can_to_input = requires { to_input_view(std::declval<_Tp>()); 
};
+    }
+
+    struct _ToInput : __adaptor::_RangeAdaptorClosure<_ToInput>
+    {
+      template<viewable_range _Range>
+       requires __detail::__can_to_input<_Range>
+       constexpr auto
+       operator() [[nodiscard]] (_Range&& __r) const
+       {
+         if constexpr (input_range<_Range>
+                       && !common_range<_Range>
+                       && !forward_range<_Range>)
+           return views::all(std::forward<_Range>(__r));
+         else
+           return to_input_view(std::forward<_Range>(__r));
+       }
+
+      static constexpr bool _S_has_simple_call_op = true;
+    };
+
+    inline constexpr _ToInput to_input;
+  }
+} // namespace ranges
+#endif // __cpp_lib_ranges_to_input
+
 _GLIBCXX_END_NAMESPACE_VERSION
 } // namespace std
 #endif // library concepts
diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/to_input/1.cc 
b/libstdc++-v3/testsuite/std/ranges/adaptors/to_input/1.cc
new file mode 100644
index 00000000000..cde368a2f64
--- /dev/null
+++ b/libstdc++-v3/testsuite/std/ranges/adaptors/to_input/1.cc
@@ -0,0 +1,59 @@
+// { dg-do run { target c++26 } }
+
+#include <ranges>
+
+#if __cpp_lib_ranges_to_input != 202502L
+# error "Feature-test macro __cpp_lib_ranges_to_input has wrong value in 
<ranges>"
+#endif
+
+#include <algorithm>
+#include <vector>
+#include <testsuite_hooks.h>
+#include <testsuite_iterators.h>
+
+namespace ranges = std::ranges;
+namespace views = std::views;
+
+void
+test01()
+{
+  std::vector<int> r{1,2,3};
+  auto v = r | views::to_input;
+  using type = decltype(v);
+  static_assert( ranges::input_range<type> && !ranges::forward_range<type> );
+
+  VERIFY( ranges::equal(v.base(), r) );
+  VERIFY( v.size() == r.size() );
+  VERIFY( v.end() == r.end() );
+  auto it = v.begin();
+  VERIFY( it != r.end() );
+  *it = 42;
+  ++it;
+  *it = 43;
+  it++;
+  ranges::iter_swap(v.begin(), it);
+  VERIFY( ranges::equal(r, (int[]){3,43,42}) );
+  *it = ranges::iter_move(it);
+  VERIFY( it == r.begin() + 2 );
+  VERIFY( r.end() - it == 1 );
+  VERIFY( it - r.end() == -1 );
+}
+
+void
+test02()
+{
+  int x[] = {1,2,3};
+  __gnu_test::test_input_range<int> rx(x);
+  static_assert( !ranges::common_range<decltype(rx)> );
+  auto v = rx | views::to_input;
+  static_assert( std::same_as<decltype(v), decltype(views::all(rx))> );
+  static_assert( std::same_as<decltype(x | views::to_input),
+                             decltype(x | views::to_input | views::to_input)> 
);
+}
+
+int
+main()
+{
+  test01();
+  test02();
+}
-- 
2.49.0.rc1.37.ge969bc8759

> 
>       In file included from 
> src/libstdc++-v3/testsuite/std/ranges/adaptors/to_input/1.cc:3:
>       /scratchpad/gcc-build/x86_64-pc-linux-gnu/libstdc++-v3/include/ranges: 
> In instantiation of ‘constexpr void std::ranges::iter_swap(const 
> to_input_view<ref_view<std::__debug::vector<int> >
>       >::_Iterator<true>&, const 
> to_input_view<ref_view<std::__debug::vector<int> > >::_Iterator<true>&) 
> requires  
> indirectly_swappable<decltype(std::ranges::__access::__begin((declval<typename
>       std::__conditional<_Const>::type<const _Vp, _Vp>&>)())), 
> decltype(std::ranges::__access::__begin((declval<typename 
> std::__conditional<_Const>::type<const _Vp, _Vp>&>)()))>’:
>       
> /scratchpad/gcc-build/x86_64-pc-linux-gnu/libstdc++-v3/include/bits/iterator_concepts.h:949:15:
>    required from ‘constexpr void 
> std::ranges::__iswap::_IterSwap::operator()(_Tp&&, _Up&&) const
>       [with _Tp = 
> std::ranges::to_input_view<std::ranges::ref_view<std::__debug::vector<int> > 
> >::_Iterator<true>; _Up = 
> std::ranges::to_input_view<std::ranges::ref_view<std::__debug::vector<int> >
>       >::_Iterator<true>&]’
>         949 |             iter_swap(static_cast<_Tp&&>(__e1), 
> static_cast<_Up&&>(__e2));
>             |             
> ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>       src/libstdc++-v3/testsuite/std/ranges/adaptors/to_input/1.cc:34:20:   
> required from here
>          34 |   ranges::iter_swap(v.begin(), it);
>             |   ~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~
>       
> /scratchpad/gcc-build/x86_64-pc-linux-gnu/libstdc++-v3/include/ranges:10529:21:
>  error: static assertion failed
>       10529 |     { static_assert(false); ranges::iter_swap(__x._M_current, 
> __y._M_current); }
>             |                     ^~~~~
>       
> /scratchpad/gcc-build/x86_64-pc-linux-gnu/libstdc++-v3/include/ranges:10529:21:
>  note: ‘false’ evaluates to false
> 
>       >       +  VERIFY( ranges::equal(r, (int[]){3,43,42}) );
>       >       +  *it = ranges::iter_move(it);
>       >       +  VERIFY( it == r.begin() + 2 );
>       >       +  VERIFY( r.end() - it == 1 );
>       >       +  VERIFY( it - r.end() == -1 );
>       >       +}
>       >       +
>       >       +void
>       >       +test02()
>       >       +{
>       >       +  int x[] = {1,2,3};
>       >       +  __gnu_test::test_input_range<int> rx(x);
>       >       +  static_assert( !ranges::common_range<decltype(rx)> );
>       >       +  auto v = rx | views::to_input;
>       >       +  using type = decltype(v);
>       >       +  using type = ranges::ref_view<decltype(rx)>;
>       >
>       > I would prefer a more direct representation of this check, as 
> static_assert(std::is_same_v<decltype(views::all(rx)), decltype())>);
> 
>       Sounds good.  The 'using' technique doesn't add much here since the type
>       names are short and we don't subsequently use the alias anywhere.
> 
>       >       +}
>       >       +
>       >       +int
>       >       +main()
>       >       +{
>       >       +  test01();
>       >       +  test02();
>       >       +}
>       >       --
>       >       2.49.0.rc1.37.ge969bc8759
>       >
>       >
>       >
> 
> 
> 

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