From 3ad39e9878310e5317ee73c9b353c1e2c1c5c4ee Mon Sep 17 00:00:00 2001
From: Richard Qin <richard.qin.x@gmail.com>
Date: Sat, 11 Jul 2026 22:48:30 +0800
Subject: lib: establish Zircon libc++ and KTL foundation

---
 .../libcxx/include/c++/v1/__variant/monostate.h    | 66 ++++++++++++++++++++++
 1 file changed, 66 insertions(+)
 create mode 100644 third_party/libcxx/include/c++/v1/__variant/monostate.h

(limited to 'third_party/libcxx/include/c++/v1/__variant')

diff --git a/third_party/libcxx/include/c++/v1/__variant/monostate.h b/third_party/libcxx/include/c++/v1/__variant/monostate.h
new file mode 100644
index 0000000..3939e42
--- /dev/null
+++ b/third_party/libcxx/include/c++/v1/__variant/monostate.h
@@ -0,0 +1,66 @@
+// -*- 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___VARIANT_MONOSTATE_H
+#define _LIBCPP___VARIANT_MONOSTATE_H
+
+#include <__compare/ordering.h>
+#include <__config>
+#include <__cstddef/size_t.h>
+#include <__functional/hash.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 17
+
+struct monostate {};
+
+_LIBCPP_HIDE_FROM_ABI inline constexpr bool operator==(monostate, monostate) noexcept { return true; }
+
+#  if _LIBCPP_STD_VER >= 20
+
+_LIBCPP_HIDE_FROM_ABI inline constexpr strong_ordering operator<=>(monostate, monostate) noexcept {
+  return strong_ordering::equal;
+}
+
+#  else // _LIBCPP_STD_VER >= 20
+
+_LIBCPP_HIDE_FROM_ABI inline constexpr bool operator!=(monostate, monostate) noexcept { return false; }
+
+_LIBCPP_HIDE_FROM_ABI inline constexpr bool operator<(monostate, monostate) noexcept { return false; }
+
+_LIBCPP_HIDE_FROM_ABI inline constexpr bool operator>(monostate, monostate) noexcept { return false; }
+
+_LIBCPP_HIDE_FROM_ABI inline constexpr bool operator<=(monostate, monostate) noexcept { return true; }
+
+_LIBCPP_HIDE_FROM_ABI inline constexpr bool operator>=(monostate, monostate) noexcept { return true; }
+
+#  endif // _LIBCPP_STD_VER >= 20
+
+template <>
+struct hash<monostate> {
+#  if _LIBCPP_STD_VER <= 17 || defined(_LIBCPP_ENABLE_CXX20_REMOVED_BINDER_TYPEDEFS)
+  using argument_type _LIBCPP_DEPRECATED_IN_CXX17 = monostate;
+  using result_type _LIBCPP_DEPRECATED_IN_CXX17   = size_t;
+#  endif
+
+  inline _LIBCPP_HIDE_FROM_ABI size_t operator()(const monostate&) const noexcept {
+    return 66740831; // return a fundamentally attractive random value.
+  }
+};
+
+#endif // _LIBCPP_STD_VER >= 17
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___VARIANT_MONOSTATE_H
-- 
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