Assume the presence of c++20 ranges

Author: ericniebler

include/stdexec/__detail/__ranges.hpp

@@ -17,11 +17,9 @@
 
 #include "__config.hpp"
 
-#if !STDEXEC_NO_STDCPP_RANGES()
+#include <ranges>
 
-#  include <ranges>
-
-#  include "__prologue.hpp"
+#include "__prologue.hpp"
 
 namespace STDEXEC::ranges
 {
@@ -34,94 +32,4 @@ namespace STDEXEC::ranges
   using std::ranges::sentinel_t;
 }  // namespace STDEXEC::ranges
 
-#  include "__epilogue.hpp"
-
-#else
-
-#  include <iterator>
-
-#  include "__prologue.hpp"
-
-namespace STDEXEC::ranges
-{
-
-  namespace __detail
-  {
-    constexpr void begin();
-    constexpr void end();
-
-    template <class _Ty>
-    concept __has_member_begin = requires(_Ty&& __val) { static_cast<_Ty&&>(__val).begin(); };
-
-    template <class _Ty>
-    concept __has_free_begin = __has_member_begin<_Ty>
-                            || requires(_Ty&& __val) { begin((static_cast<_Ty&&>(__val))); };
-
-    template <class _Ty>
-    concept __has_member_end = requires(_Ty&& __val) { static_cast<_Ty&&>(__val).end(); };
-
-    template <class _Ty>
-    concept __has_free_end = __has_member_end<_Ty>
-                          || requires(_Ty&& __val) { end((static_cast<_Ty&&>(__val))); };
-
-    struct __begin_t
-    {
-      template <class _Range>
-        requires __has_member_begin<_Range>
-      auto
-      operator()(_Range&& __rng) const noexcept(noexcept((static_cast<_Range&&>(__rng)).begin()))
-        -> decltype((static_cast<_Range&&>(__rng)).begin())
-      {
-        return static_cast<_Range&&>(__rng).begin();
-      }
-
-      template <class _Range>
-        requires __has_free_begin<_Range>
-      auto
-      operator()(_Range&& __rng) const noexcept(noexcept(begin((static_cast<_Range&&>(__rng)))))
-        -> decltype(begin((static_cast<_Range&&>(__rng))))
-      {
-        return begin((static_cast<_Range&&>(__rng)));
-      }
-    };
-
-    struct __end_t
-    {
-      template <class _Range>
-        requires __has_member_end<_Range>
-      auto operator()(_Range&& __rng) const noexcept(noexcept((static_cast<_Range&&>(__rng)).end()))
-        -> decltype((static_cast<_Range&&>(__rng)).end())
-      {
-        return static_cast<_Range&&>(__rng).end();
-      }
-
-      template <class _Range>
-        requires __has_free_end<_Range>
-      auto operator()(_Range&& __rng) const noexcept(noexcept(end((static_cast<_Range&&>(__rng)))))
-        -> decltype(end((static_cast<_Range&&>(__rng))))
-      {
-        return end((static_cast<_Range&&>(__rng)));
-      }
-    };
-  }  // namespace __detail
-
-  inline constexpr __detail::__begin_t begin{};
-  inline constexpr __detail::__end_t   end{};
-
-  template <class _Range>
-  using iterator_t = decltype(begin((__declval<_Range>())));
-
-  template <class _Range>
-  using sentinel_t = decltype(end((__declval<_Range>())));
-
-  template <class _Range>
-  using range_reference_t = decltype(*begin((__declval<_Range>())));
-
-  template <class _Range>
-  using range_value_t = std::iterator_traits<iterator_t<_Range>>::value_type;
-
-}  // namespace STDEXEC::ranges
-
-#  include "__epilogue.hpp"
-
-#endif
+#include "__epilogue.hpp"