[libcxx-commits] [libcxx] [libc++] Introduce a standalone __scope_guard and use it in <string> (PR #114867)

[A. Jiang via libcxx-commits]

================
@@ -0,0 +1,46 @@
+// -*- 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___UTILITY_SCOPE_GUARD_H
+#define _LIBCPP___UTILITY_SCOPE_GUARD_H
+
+#include <__config>
+#include <__utility/move.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class _Func>
+class __scope_guard {
+  _Func __func_;
+
+public:
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR __scope_guard(_Func __func) : __func_(std::move(__func)) {}
+  _LIBCPP_HIDE_FROM_ABI ~__scope_guard() { __func_(); }
+
+  __scope_guard(const __scope_guard&)            = delete;
+  __scope_guard& operator=(const __scope_guard&) = delete;
+};
+
+template <class _Func>
+__scope_guard<_Func> __make_scope_guard(_Func __func) {
----------------
frederick-vs-ja wrote:

```suggestion
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __scope_guard<_Func> __make_scope_guard(_Func __func) {
```

There seem to be other missing occurrences of `_LIBCPP_CONSTEXPR_SINCE_CXX20`.

https://github.com/llvm/llvm-project/pull/114867