[libcxx-commits] [libcxx] [libc++][memory] P1132R8: `out_ptr` - a scalable output pointer abstraction (PR #73618)

[David Benjamin via libcxx-commits]

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@@ -0,0 +1,109 @@
+// -*- 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___INOUT_PTR_H
+#define _LIBCPP___INOUT_PTR_H
+
+#include <__config>
+#include <__memory/addressof.h>
+#include <__memory/pointer_traits.h>
+#include <__memory/shared_ptr.h>
+#include <__memory/unique_ptr.h>
+#include <__type_traits/is_same.h>
+#include <__type_traits/is_specialization.h>
+#include <__type_traits/is_void.h>
+#include <__utility/forward.h>
+#include <__utility/move.h>
+#include <tuple>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 23
+
+template <class _Smart, class _Pointer, class... _Args>
+class _LIBCPP_TEMPLATE_VIS inout_ptr_t {
+  static_assert(!__is_specialization_v<_Smart, shared_ptr>, "std::shared_ptr<> is not supported with std::inout_ptr.");
+
+public:
+  _LIBCPP_HIDE_FROM_ABI explicit inout_ptr_t(_Smart& __smart, _Args... __args)
+      : __s_(__smart), __a_(std::forward<_Args>(__args)...), __p_([&__smart] {
+          if constexpr (is_pointer_v<_Smart>) {
+            return __smart;
+          } else {
+            return __smart.get();
+          }
+        }()) {
+    if constexpr (requires { __s_.release(); }) {
+      __s_.release();
+    } else {
+      __s_ = _Smart();
+    }
+  }
+
+  _LIBCPP_HIDE_FROM_ABI inout_ptr_t(const inout_ptr_t&) = delete;
+
+  _LIBCPP_HIDE_FROM_ABI ~inout_ptr_t() {
+    // LWG-3897 inout_ptr will not update raw pointer to null
+    if constexpr (!is_pointer_v<_Smart>) {
+      if (!__p_) {
+        return;
+      }
+    }
+
+    using _SP = __pointer_of_or_t<_Smart, _Pointer>;
+    if constexpr (is_pointer_v<_Smart>) {
+      std::apply([&](auto&&... __args) { __s_ = _Smart(static_cast<_SP>(__p_), std::forward<_Args>(__args)...); },
+                 std::move(__a_));
+    } else if constexpr (__resettable_smart_pointer_with_args<_Smart, _Pointer, _Args...>) {
+      std::apply([&](auto&&... __args) { __s_.reset(static_cast<_SP>(__p_), std::forward<_Args>(__args)...); },
+                 std::move(__a_));
+    } else {
+      static_assert(is_constructible_v<_Smart, _SP, _Args...>,
+                    "The smart pointer must be constructible from arguments of types _Smart, _Pointer, _Args...");
+      std::apply([&](auto&&... __args) { __s_ = _Smart(static_cast<_SP>(__p_), std::forward<_Args>(__args)...); },
+                 std::move(__a_));
+    }
+  }
+
+  _LIBCPP_HIDE_FROM_ABI operator _Pointer*() const noexcept { return std::addressof(const_cast<_Pointer&>(__p_)); }
+
+  _LIBCPP_HIDE_FROM_ABI operator void**() const noexcept
+    requires(!is_same_v<_Pointer, void*>)
+  {
+    static_assert(is_pointer_v<_Pointer>, "The conversion to void** requires _Pointer to be a raw pointer.");
+
+    return reinterpret_cast<void**>(static_cast<_Pointer*>(*this));
----------------
davidben wrote:

Drive-by comment: Is this cast actually strictly legal? See https://github.com/llvm/llvm-project/issues/133445

https://github.com/llvm/llvm-project/pull/73618