[PATCH] libstdc++: Implement ranges::repeat_view from P2474R2

[PATCH] libstdc++: Implement ranges::repeat_view from P2474R2

[Patrick Palka]

Tested on x86_64-pc-linux-gnu, does this look OK for trunk? (The paper
also makes changes to views::take and views::drop, which will be
implemented separately.)

libstdc++-v3/ChangeLog:

	* include/std/ranges (repeat_view): Define.
	(repeat_view::_Iterator): Define.
	(views::__detail::__can_repeat_view): Define.
	(views::__detail::__can_bounded_repeat_view): Define.
	(views::_Repeat, views::repeat): Define.
	* testsuite/std/ranges/repeat/1.cc: New test.
---
 libstdc++-v3/include/std/ranges               | 210 ++++++++++++++++++
 libstdc++-v3/testsuite/std/ranges/repeat/1.cc |  93 ++++++++
 2 files changed, 303 insertions(+)
 create mode 100644 libstdc++-v3/testsuite/std/ranges/repeat/1.cc

diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 1f821128d2d..5857d426a66 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -7356,6 +7356,216 @@ namespace views::__adaptor
 
     inline constexpr _JoinWith join_with;
   } // namespace views
+
+  template<copy_constructible _Tp, semiregular _Bound = unreachable_sentinel_t>
+    requires (is_object_v<_Tp> && same_as<_Tp, remove_cv_t<_Tp>>
+      && (__detail::__is_integer_like<_Bound> || same_as<_Bound, unreachable_sentinel_t>))
+  class repeat_view : public view_interface<repeat_view<_Tp, _Bound>>
+  {
+    __detail::__box<_Tp> _M_value = _Tp();
+    [[no_unique_address]] _Bound _M_bound = _Bound();
+
+    struct _Iterator;
+
+  public:
+    repeat_view() requires default_initializable<_Tp> = default;
+
+    constexpr explicit
+    repeat_view(const _Tp& __value, _Bound __bound = _Bound())
+    : _M_value(__value), _M_bound(__bound)
+    {
+      if constexpr (!same_as<_Bound, unreachable_sentinel_t>)
+	__glibcxx_assert(__bound >= 0);
+    }
+
+    constexpr explicit
+    repeat_view(_Tp&& __value, _Bound __bound = _Bound())
+    : _M_value(std::move(__value)), _M_bound(__bound)
+    { }
+
+    template<typename... _Args, typename... _BoundArgs>
+      requires constructible_from<_Tp, _Args...>
+        && constructible_from<_Bound, _BoundArgs...>
+    constexpr explicit
+    repeat_view(piecewise_construct_t,
+		tuple<_Args...> __args,
+		tuple<_BoundArgs...> __bound_args = tuple<>{})
+    : _M_value(std::make_from_tuple<_Tp>(std::move(__args))),
+      _M_bound(std::make_from_tuple<_Bound>(std::move(__bound_args)))
+    { }
+
+    constexpr _Iterator
+    begin() const
+    { return _Iterator(std::__addressof(*_M_value)); }
+
+    constexpr _Iterator
+    end() const requires (!same_as<_Bound, unreachable_sentinel_t>)
+    { return _Iterator(std::__addressof(*_M_value), _M_bound); }
+
+    constexpr unreachable_sentinel_t
+    end() const noexcept
+    { return unreachable_sentinel; }
+
+    constexpr auto
+    size() const requires (!same_as<_Bound, unreachable_sentinel_t>)
+    { return __detail::__to_unsigned_like(_M_bound); }
+  };
+
+  template<typename _Tp, typename _Bound>
+    repeat_view(_Tp, _Bound) -> repeat_view<_Tp, _Bound>;
+
+  template<copy_constructible _Tp, semiregular _Bound>
+    requires __detail::__is_integer_like<_Bound> || same_as<_Bound, unreachable_sentinel_t>
+  class repeat_view<_Tp, _Bound>::_Iterator
+  {
+    using __index_type
+      = __conditional_t<same_as<_Bound, unreachable_sentinel_t>, ptrdiff_t, _Bound>;
+
+    const _Tp* _M_value = nullptr;
+    __index_type _M_current = __index_type();
+
+    constexpr explicit
+    _Iterator(const _Tp* __value, __index_type __bound = __index_type())
+    : _M_value(__value), _M_current(__bound)
+    {
+      if constexpr (!same_as<_Bound, unreachable_sentinel_t>)
+	__glibcxx_assert(__bound >= 0);
+    }
+
+    friend repeat_view;
+
+  public:
+    using iterator_concept = random_access_iterator_tag;
+    using iterator_category = random_access_iterator_tag;
+    using value_type = _Tp;
+    using difference_type = __conditional_t<__detail::__is_signed_integer_like<__index_type>,
+					    __index_type,
+					    __detail::__iota_diff_t<__index_type>>;
+
+    _Iterator() = default;
+
+    constexpr const _Tp&
+    operator*() const noexcept
+    { return *_M_value; }
+
+    constexpr _Iterator&
+    operator++()
+    {
+      ++_M_current;
+      return *this;
+    }
+
+    constexpr _Iterator
+    operator++(int)
+    {
+      auto __tmp = *this;
+      ++*this;
+      return __tmp;
+    }
+
+    constexpr _Iterator&
+    operator--()
+    {
+      if constexpr (!same_as<_Bound, unreachable_sentinel_t>)
+	__glibcxx_assert(_M_current > 0);
+      --_M_current;
+      return *this;
+    }
+
+    constexpr _Iterator
+    operator--(int)
+    {
+      auto __tmp = *this;
+      --*this;
+      return __tmp;
+    }
+
+    constexpr _Iterator&
+    operator+=(difference_type __n)
+    {
+      if constexpr (!same_as<_Bound, unreachable_sentinel_t>)
+	__glibcxx_assert(_M_current + __n >= 0);
+      _M_current += __n;
+      return *this;
+    }
+
+    constexpr _Iterator&
+    operator-=(difference_type __n)
+    {
+      if constexpr (!same_as<_Bound, unreachable_sentinel_t>)
+	__glibcxx_assert(_M_current - __n >= 0);
+      _M_current -= __n;
+      return *this;
+    }
+
+    constexpr const _Tp&
+    operator[](difference_type __n) const noexcept
+    { return *(*this + __n); }
+
+    friend constexpr bool
+    operator==(const _Iterator& __x, const _Iterator& __y)
+    { return __x._M_current == __y._M_current; }
+
+    friend constexpr auto
+    operator<=>(const _Iterator& __x, const _Iterator& __y)
+    { return __x._M_current <=> __y._M_current; }
+
+    friend constexpr _Iterator
+    operator+(_Iterator __i, difference_type __n)
+    {
+      __i += __n;
+      return __i;
+    }
+
+    friend constexpr _Iterator
+    operator+(difference_type __n, _Iterator __i)
+    { return __i + __n; }
+
+    friend constexpr _Iterator
+    operator-(_Iterator __i, difference_type __n)
+    {
+      __i -= __n;
+      return __i;
+    }
+
+    friend constexpr difference_type
+    operator-(const _Iterator& __x, const _Iterator& __y)
+    {
+      return (static_cast<difference_type>(__x._M_current)
+	      - static_cast<difference_type>(__y._M_current));
+    }
+  };
+
+  namespace views
+  {
+    namespace __detail
+    {
+      template<typename _Tp>
+	concept __can_repeat_view
+	  = requires { repeat_view(std::declval<_Tp>()); };
+
+      template<typename _Tp, typename _Bound>
+	concept __can_bounded_repeat_view
+	  = requires { repeat_view(std::declval<_Tp>(), std::declval<_Bound>()); };
+    }
+
+    struct _Repeat
+    {
+      template<typename _Tp>
+	requires __detail::__can_repeat_view<_Tp>
+      constexpr auto
+      operator() [[nodiscard]] (_Tp&& __value) const
+      { return repeat_view(std::forward<_Tp>(__value)); }
+
+      template<typename _Tp, typename _Bound>
+	requires __detail::__can_bounded_repeat_view<_Tp, _Bound>
+      constexpr auto
+      operator() [[nodiscard]] (_Tp&& __value, _Bound __bound) const
+      { return repeat_view(std::forward<_Tp>(__value), __bound); }
+    };
+
+    inline constexpr _Repeat repeat;
+  }
 #endif // C++23
 } // namespace ranges
 
diff --git a/libstdc++-v3/testsuite/std/ranges/repeat/1.cc b/libstdc++-v3/testsuite/std/ranges/repeat/1.cc
new file mode 100644
index 00000000000..3698ed12c14
--- /dev/null
+++ b/libstdc++-v3/testsuite/std/ranges/repeat/1.cc
@@ -0,0 +1,93 @@
+// { dg-options "-std=gnu++23" }
+// { dg-do run { target c++23 } }
+
+#include <ranges>
+#include <algorithm>
+#include <testsuite_hooks.h>
+
+namespace ranges = std::ranges;
+namespace views = std::views;
+
+constexpr bool
+test01()
+{
+  auto v = views::repeat(42);
+  static_assert(ranges::random_access_range<decltype(v)>
+		&& !ranges::sized_range<decltype(v)>);
+  auto i = ranges::begin(v);
+  auto s = ranges::end(v);
+  VERIFY( *i == 42 );
+  VERIFY( i[0] == 42 );
+  VERIFY( &i[0] == &i[1] );
+  VERIFY( &*i == &*(i+1) );
+  VERIFY( i != s );
+  auto j = i + 5, k = i + 12;
+  VERIFY( k - i == 12 );
+  VERIFY( k - j == 7 );
+  VERIFY( i - j == -5 );
+  VERIFY( k > j );
+  VERIFY( j < k );
+  VERIFY( i + 5 == j );
+  VERIFY( i != j );
+  VERIFY( i + 5 <= j );
+  VERIFY( j - 5 >= i );
+
+  return true;
+}
+
+constexpr bool
+test02()
+{
+  constexpr int bound = 20;
+  auto v = views::repeat(42, bound);
+  static_assert(ranges::random_access_range<decltype(v)>
+		&& ranges::sized_range<decltype(v)>);
+  VERIFY( ranges::equal(v, views::repeat(42) | views::take(bound)) );
+  auto i = ranges::begin(v);
+  auto s = ranges::end(v);
+  VERIFY( *i == 42 );
+  VERIFY( i[0] == 42 );
+  VERIFY( &i[0] == &i[1] );
+  VERIFY( &*i == &*(i+1) );
+  VERIFY( i != s );
+  auto j = i + 5, k = i + 12;
+  VERIFY( k - i == 12 );
+  VERIFY( k - j == 7 );
+  VERIFY( i - j == -5 );
+  VERIFY( k > j );
+  VERIFY( j < k );
+  VERIFY( i + 5 == j );
+  VERIFY( i != j );
+  VERIFY( i + 5 <= j );
+  VERIFY( j - 5 >= i );
+
+  VERIFY( ranges::size(v) == bound );
+  VERIFY( s - i == bound );
+  VERIFY( s - j == bound - (j - i) );
+  VERIFY( i + bound == s );
+  VERIFY( bound + i == s );
+
+  return true;
+}
+
+constexpr bool
+test03()
+{
+  struct A { int n, m; };
+  auto v = ranges::repeat_view<A, unsigned>(std::piecewise_construct,
+					    std::tuple{1, 2},
+					    std::tuple{3});
+  VERIFY( v[0].n == 1 );
+  VERIFY( v[0].m == 2 );
+  VERIFY( ranges::size(v) == 3 );
+
+  return true;
+}
+
+int
+main()
+{
+  static_assert(test01());
+  static_assert(test02());
+  static_assert(test03());
+}
-- 
2.38.0.15.gbbe21b64a0

Re: [PATCH] libstdc++: Implement ranges::repeat_view from P2474R2

[Jonathan Wakely]

On Tue, 11 Oct 2022 at 03:51, Patrick Palka via Libstdc++
<libstdc++@gcc.gnu.org> wrote:
>
> Tested on x86_64-pc-linux-gnu, does this look OK for trunk? (The paper
> also makes changes to views::take and views::drop, which will be
> implemented separately.)

OK, thanks.

[PATCH] libstdc++: Implement P2474R2 changes to views::take/drop

[Patrick Palka]

Tested on x86_64-pc-linux-gnu, does this look OK for trunk?

libstdc++-v3/ChangeLog:

	* include/std/ranges (views::__detail::__is_repeat_view): Define
	and later define a partial specialization.
	(views::__detail::__take_of_repeat_view): Declare and later define.
	(views::__detail::__drop_of_repeat_view): Likewise.
	(views::_Take::operator()): Return a repeat_view if the argument
	is a repeat_view as per P2474R2.
	(views::_Drop::operator()): Likewise.
	(repeat_view): Befriend __take/drop_of_repeat_view.
	* testsuite/std/ranges/repeat/1.cc (test04): New test.
---
 libstdc++-v3/include/std/ranges               | 56 +++++++++++++++++++
 libstdc++-v3/testsuite/std/ranges/repeat/1.cc | 33 +++++++++++
 2 files changed, 89 insertions(+)

diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index b29264931cc..6de08244bd1 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -2257,6 +2257,13 @@ namespace views::__adaptor
       template<typename _Winc, typename _Bound>
 	inline constexpr bool __is_iota_view<iota_view<_Winc, _Bound>> = true;
 
+      template<typename _Range>
+	inline constexpr bool __is_repeat_view = false;
+
+      template<typename _Range>
+	constexpr auto
+	__take_of_repeat_view(_Range&&, range_difference_t<_Range>); // defined later
+
       template<typename _Range, typename _Dp>
 	concept __can_take_view
 	  = requires { take_view(std::declval<_Range>(), std::declval<_Dp>()); };
@@ -2291,6 +2298,8 @@ namespace views::__adaptor
 	      else
 		return iota_view(*__begin, *__end);
 	    }
+	  else if constexpr (__detail::__is_repeat_view<_Tp>)
+	    return __detail::__take_of_repeat_view(std::forward<_Range>(__r), __n);
 	  else
 	    return take_view(std::forward<_Range>(__r), __n);
 	}
@@ -2527,6 +2536,10 @@ namespace views::__adaptor
   {
     namespace __detail
     {
+      template<typename _Range>
+	constexpr auto
+	__drop_of_repeat_view(_Range&&, range_difference_t<_Range>); // defined later
+
       template<typename _Range, typename _Dp>
 	concept __can_drop_view
 	  = requires { drop_view(std::declval<_Range>(), std::declval<_Dp>()); };
@@ -2568,6 +2581,8 @@ namespace views::__adaptor
 	      else
 		return _Tp(__begin, __end);
 	    }
+	  else if constexpr (__detail::__is_repeat_view<_Tp>)
+	    return __detail::__drop_of_repeat_view(std::forward<_Range>(__r), __n);
 	  else
 	    return drop_view(std::forward<_Range>(__r), __n);
 	}
@@ -7367,6 +7382,14 @@ namespace views::__adaptor
 
     struct _Iterator;
 
+    template<typename _Range>
+      friend constexpr auto
+      views::__detail::__take_of_repeat_view(_Range&&, range_difference_t<_Range>);
+
+    template<typename _Range>
+      friend constexpr auto
+      views::__detail::__drop_of_repeat_view(_Range&&, range_difference_t<_Range>);
+
   public:
     repeat_view() requires default_initializable<_Tp> = default;
 
@@ -7540,6 +7563,9 @@ namespace views::__adaptor
   {
     namespace __detail
     {
+      template<typename _Tp, typename _Bound>
+	inline constexpr bool __is_repeat_view<repeat_view<_Tp, _Bound>> = true;
+
       template<typename _Tp>
 	concept __can_repeat_view
 	  = requires { repeat_view(std::declval<_Tp>()); };
@@ -7565,6 +7591,36 @@ namespace views::__adaptor
     };
 
     inline constexpr _Repeat repeat;
+
+    namespace __detail
+    {
+      template<typename _Range>
+	constexpr auto
+	__take_of_repeat_view(_Range&& __r, range_difference_t<_Range> __n)
+	{
+	  using _Tp = remove_cvref_t<_Range>;
+	  static_assert(__is_repeat_view<_Tp>);
+	  if constexpr (sized_range<_Tp>)
+	    return views::repeat(*__r._M_value, std::min(ranges::distance(__r), __n));
+	  else
+	    return views::repeat(*__r._M_value, __n);
+	}
+
+      template<typename _Range>
+	constexpr auto
+	__drop_of_repeat_view(_Range&& __r, range_difference_t<_Range> __n)
+	{
+	  using _Tp = remove_cvref_t<_Range>;
+	  static_assert(__is_repeat_view<_Tp>);
+	  if constexpr (sized_range<_Tp>)
+	    {
+	      auto __sz = ranges::distance(__r);
+	      return views::repeat(*__r._M_value, __sz - std::min(__sz, __n));
+	    }
+	  else
+	    return __r;
+	}
+    }
   }
 
   template<input_range _Vp>
diff --git a/libstdc++-v3/testsuite/std/ranges/repeat/1.cc b/libstdc++-v3/testsuite/std/ranges/repeat/1.cc
index 3698ed12c14..542c8614f88 100644
--- a/libstdc++-v3/testsuite/std/ranges/repeat/1.cc
+++ b/libstdc++-v3/testsuite/std/ranges/repeat/1.cc
@@ -84,10 +84,43 @@ test03()
   return true;
 }
 
+constexpr bool
+test04()
+{
+  // Verify P2472R2 changes to views::take/drop.
+  auto r = views::repeat(42);
+
+  auto rt = r | views::take(10);
+  static_assert(views::__detail::__is_repeat_view<decltype(rt)>);
+  VERIFY( ranges::equal(rt, views::repeat(42, 10)) );
+
+  auto rd = r | views::drop(10);
+  static_assert(std::same_as<decltype(rd), decltype(r)>);
+
+  auto br = views::repeat(42, 37);
+
+  auto brt = br | views::take(10);
+  static_assert(std::same_as<decltype(brt), decltype(br)>);
+  VERIFY( ranges::equal(brt, views::repeat(42, 10)) );
+
+  auto brt100 = br | views::take(100);
+  VERIFY( ranges::equal(brt100, br) );
+
+  auto brd = br | views::drop(10);
+  static_assert(std::same_as<decltype(brd), decltype(br)>);
+  VERIFY( ranges::equal(brd, views::repeat(42, 27)) );
+
+  auto brd100 = br | views::drop(100);
+  VERIFY( ranges::empty(brd100) );
+
+  return true;
+}
+
 int
 main()
 {
   static_assert(test01());
   static_assert(test02());
   static_assert(test03());
+  static_assert(test04());
 }
-- 
2.38.1.119.g9c32cfb49c

Re: [PATCH] libstdc++: Implement P2474R2 changes to views::take/drop

[Jonathan Wakely]

[-- Attachment #1: Type: text/plain, Size: 6398 bytes --]

On Wed, 19 Oct 2022, 17:47 Patrick Palka via Libstdc++, <
libstdc++@gcc.gnu.org> wrote:

> Tested on x86_64-pc-linux-gnu, does this look OK for trunk?
>

OK



> libstdc++-v3/ChangeLog:
>
>         * include/std/ranges (views::__detail::__is_repeat_view): Define
>         and later define a partial specialization.
>         (views::__detail::__take_of_repeat_view): Declare and later define.
>         (views::__detail::__drop_of_repeat_view): Likewise.
>         (views::_Take::operator()): Return a repeat_view if the argument
>         is a repeat_view as per P2474R2.
>         (views::_Drop::operator()): Likewise.
>         (repeat_view): Befriend __take/drop_of_repeat_view.
>         * testsuite/std/ranges/repeat/1.cc (test04): New test.
> ---
>  libstdc++-v3/include/std/ranges               | 56 +++++++++++++++++++
>  libstdc++-v3/testsuite/std/ranges/repeat/1.cc | 33 +++++++++++
>  2 files changed, 89 insertions(+)
>
> diff --git a/libstdc++-v3/include/std/ranges
> b/libstdc++-v3/include/std/ranges
> index b29264931cc..6de08244bd1 100644
> --- a/libstdc++-v3/include/std/ranges
> +++ b/libstdc++-v3/include/std/ranges
> @@ -2257,6 +2257,13 @@ namespace views::__adaptor
>        template<typename _Winc, typename _Bound>
>         inline constexpr bool __is_iota_view<iota_view<_Winc, _Bound>> =
> true;
>
> +      template<typename _Range>
> +       inline constexpr bool __is_repeat_view = false;
> +
> +      template<typename _Range>
> +       constexpr auto
> +       __take_of_repeat_view(_Range&&, range_difference_t<_Range>); //
> defined later
> +
>        template<typename _Range, typename _Dp>
>         concept __can_take_view
>           = requires { take_view(std::declval<_Range>(),
> std::declval<_Dp>()); };
> @@ -2291,6 +2298,8 @@ namespace views::__adaptor
>               else
>                 return iota_view(*__begin, *__end);
>             }
> +         else if constexpr (__detail::__is_repeat_view<_Tp>)
> +           return
> __detail::__take_of_repeat_view(std::forward<_Range>(__r), __n);
>           else
>             return take_view(std::forward<_Range>(__r), __n);
>         }
> @@ -2527,6 +2536,10 @@ namespace views::__adaptor
>    {
>      namespace __detail
>      {
> +      template<typename _Range>
> +       constexpr auto
> +       __drop_of_repeat_view(_Range&&, range_difference_t<_Range>); //
> defined later
> +
>        template<typename _Range, typename _Dp>
>         concept __can_drop_view
>           = requires { drop_view(std::declval<_Range>(),
> std::declval<_Dp>()); };
> @@ -2568,6 +2581,8 @@ namespace views::__adaptor
>               else
>                 return _Tp(__begin, __end);
>             }
> +         else if constexpr (__detail::__is_repeat_view<_Tp>)
> +           return
> __detail::__drop_of_repeat_view(std::forward<_Range>(__r), __n);
>           else
>             return drop_view(std::forward<_Range>(__r), __n);
>         }
> @@ -7367,6 +7382,14 @@ namespace views::__adaptor
>
>      struct _Iterator;
>
> +    template<typename _Range>
> +      friend constexpr auto
> +      views::__detail::__take_of_repeat_view(_Range&&,
> range_difference_t<_Range>);
> +
> +    template<typename _Range>
> +      friend constexpr auto
> +      views::__detail::__drop_of_repeat_view(_Range&&,
> range_difference_t<_Range>);
> +
>    public:
>      repeat_view() requires default_initializable<_Tp> = default;
>
> @@ -7540,6 +7563,9 @@ namespace views::__adaptor
>    {
>      namespace __detail
>      {
> +      template<typename _Tp, typename _Bound>
> +       inline constexpr bool __is_repeat_view<repeat_view<_Tp, _Bound>> =
> true;
> +
>        template<typename _Tp>
>         concept __can_repeat_view
>           = requires { repeat_view(std::declval<_Tp>()); };
> @@ -7565,6 +7591,36 @@ namespace views::__adaptor
>      };
>
>      inline constexpr _Repeat repeat;
> +
> +    namespace __detail
> +    {
> +      template<typename _Range>
> +       constexpr auto
> +       __take_of_repeat_view(_Range&& __r, range_difference_t<_Range> __n)
> +       {
> +         using _Tp = remove_cvref_t<_Range>;
> +         static_assert(__is_repeat_view<_Tp>);
> +         if constexpr (sized_range<_Tp>)
> +           return views::repeat(*__r._M_value,
> std::min(ranges::distance(__r), __n));
> +         else
> +           return views::repeat(*__r._M_value, __n);
> +       }
> +
> +      template<typename _Range>
> +       constexpr auto
> +       __drop_of_repeat_view(_Range&& __r, range_difference_t<_Range> __n)
> +       {
> +         using _Tp = remove_cvref_t<_Range>;
> +         static_assert(__is_repeat_view<_Tp>);
> +         if constexpr (sized_range<_Tp>)
> +           {
> +             auto __sz = ranges::distance(__r);
> +             return views::repeat(*__r._M_value, __sz - std::min(__sz,
> __n));
> +           }
> +         else
> +           return __r;
> +       }
> +    }
>    }
>
>    template<input_range _Vp>
> diff --git a/libstdc++-v3/testsuite/std/ranges/repeat/1.cc
> b/libstdc++-v3/testsuite/std/ranges/repeat/1.cc
> index 3698ed12c14..542c8614f88 100644
> --- a/libstdc++-v3/testsuite/std/ranges/repeat/1.cc
> +++ b/libstdc++-v3/testsuite/std/ranges/repeat/1.cc
> @@ -84,10 +84,43 @@ test03()
>    return true;
>  }
>
> +constexpr bool
> +test04()
> +{
> +  // Verify P2472R2 changes to views::take/drop.
> +  auto r = views::repeat(42);
> +
> +  auto rt = r | views::take(10);
> +  static_assert(views::__detail::__is_repeat_view<decltype(rt)>);
> +  VERIFY( ranges::equal(rt, views::repeat(42, 10)) );
> +
> +  auto rd = r | views::drop(10);
> +  static_assert(std::same_as<decltype(rd), decltype(r)>);
> +
> +  auto br = views::repeat(42, 37);
> +
> +  auto brt = br | views::take(10);
> +  static_assert(std::same_as<decltype(brt), decltype(br)>);
> +  VERIFY( ranges::equal(brt, views::repeat(42, 10)) );
> +
> +  auto brt100 = br | views::take(100);
> +  VERIFY( ranges::equal(brt100, br) );
> +
> +  auto brd = br | views::drop(10);
> +  static_assert(std::same_as<decltype(brd), decltype(br)>);
> +  VERIFY( ranges::equal(brd, views::repeat(42, 27)) );
> +
> +  auto brd100 = br | views::drop(100);
> +  VERIFY( ranges::empty(brd100) );
> +
> +  return true;
> +}
> +
>  int
>  main()
>  {
>    static_assert(test01());
>    static_assert(test02());
>    static_assert(test03());
> +  static_assert(test04());
>  }
> --
> 2.38.1.119.g9c32cfb49c
>
>