1 files changed, 132 insertions, 0 deletions
diff --git a/libcxx/include/__ranges/size.h b/libcxx/include/__ranges/size.h
new file mode 100644
index 000000000000..ce7183e15447
--- /dev/null
+++ b/libcxx/include/__ranges/size.h
@@ -0,0 +1,132 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+#ifndef _LIBCPP___RANGES_SIZE_H
+#define _LIBCPP___RANGES_SIZE_H
+
+#include <__config>
+#include <__iterator/concepts.h>
+#include <__iterator/iterator_traits.h>
+#include <__ranges/access.h>
+#include <__utility/__decay_copy.h>
+#include <__utility/forward.h>
+#include <concepts>
+#include <type_traits>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#pragma GCC system_header
+#endif
+
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if !defined(_LIBCPP_HAS_NO_RANGES)
+
+// clang-format off
+namespace ranges {
+template<class>
+inline constexpr bool disable_sized_range = false;
+
+// [range.prim.size]
+namespace __size {
+  void size(auto&) = delete;
+  void size(const auto&) = delete;
+
+  template <class _Tp>
+  concept __size_enabled = !disable_sized_range<remove_cvref_t<_Tp>>;
+
+  template <class _Tp>
+  concept __member_size = __size_enabled<_Tp> && requires(_Tp&& __t) {
+    { _VSTD::__decay_copy(_VSTD::forward<_Tp>(__t).size()) } -> __integer_like;
+  };
+
+  template <class _Tp>
+  concept __unqualified_size =
+    __size_enabled<_Tp> &&
+    !__member_size<_Tp> &&
+    __class_or_enum<remove_cvref_t<_Tp>> &&
+    requires(_Tp&& __t) {
+      { _VSTD::__decay_copy(size(_VSTD::forward<_Tp>(__t))) } -> __integer_like;
+    };
+
+  template <class _Tp>
+  concept __difference =
+    !__member_size<_Tp> &&
+    !__unqualified_size<_Tp> &&
+    __class_or_enum<remove_cvref_t<_Tp>> &&
+    requires(_Tp&& __t) {
+      { ranges::begin(__t) } -> forward_iterator;
+      { ranges::end(__t) } -> sized_sentinel_for<decltype(ranges::begin(declval<_Tp>()))>;
+    };
+
+  struct __fn {
+    template <class _Tp, size_t _Sz>
+    [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr size_t operator()(_Tp (&&)[_Sz]) const noexcept {
+      return _Sz;
+    }
+
+    template <class _Tp, size_t _Sz>
+    [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr size_t operator()(_Tp (&)[_Sz]) const noexcept {
+      return _Sz;
+    }
+
+    template <__member_size _Tp>
+    [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr __integer_like auto operator()(_Tp&& __t) const
+        noexcept(noexcept(_VSTD::forward<_Tp>(__t).size())) {
+      return _VSTD::forward<_Tp>(__t).size();
+    }
+
+    template <__unqualified_size _Tp>
+    [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr __integer_like auto operator()(_Tp&& __t) const
+        noexcept(noexcept(size(_VSTD::forward<_Tp>(__t)))) {
+      return size(_VSTD::forward<_Tp>(__t));
+    }
+
+    template<__difference _Tp>
+    [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr __integer_like auto operator()(_Tp&& __t) const
+        noexcept(noexcept(ranges::end(__t) - ranges::begin(__t))) {
+      return _VSTD::__to_unsigned_like(ranges::end(__t) - ranges::begin(__t));
+    }
+  };
+} // end namespace __size
+
+inline namespace __cpo {
+  inline constexpr auto size = __size::__fn{};
+} // namespace __cpo
+
+namespace __ssize {
+  struct __fn {
+    template<class _Tp>
+      requires requires (_Tp&& __t) { ranges::size(__t); }
+    [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr integral auto operator()(_Tp&& __t) const
+        noexcept(noexcept(ranges::size(__t))) {
+      using _Signed = make_signed_t<decltype(ranges::size(__t))>;
+      if constexpr (sizeof(ptrdiff_t) > sizeof(_Signed))
+        return static_cast<ptrdiff_t>(ranges::size(__t));
+      else
+        return static_cast<_Signed>(ranges::size(__t));
+    }
+  };
+}
+
+inline namespace __cpo {
+  inline constexpr const auto ssize = __ssize::__fn{};
+} // namespace __cpo
+} // namespace ranges
+
+// clang-format off
+
+#endif // !defined(_LIBCPP_HAS_NO_RANGES)
+
+_LIBCPP_END_NAMESPACE_STD
+
+_LIBCPP_POP_MACROS
+
+#endif // _LIBCPP___RANGES_SIZE_H