[libcxx-commits] [libcxx] [libc++] Add container_traits (prework for `std::flat_map`) (PR #109578)

[via libcxx-commits]

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@@ -0,0 +1,28 @@
+// -*- 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___TYPE_TRAITS_CONTAINER_TRAITS_H
+#define _LIBCPP___TYPE_TRAITS_CONTAINER_TRAITS_H
+
+#include <__config>
+#include <__type_traits/integral_constant.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class _Tp>
+struct __container_traits {
+  using __emplacement_has_strong_exception_safety_guarantee = false_type;
----------------
huixie90 wrote:

> Why is this a `bool_constant`? Is it expected to be used in `_And`/`_Or`?

`bool_constant` definitely works in C++03 and others I am not too sure. as Louis pointed out, we can potentially use 
```
static _LIBCPP_CONSTEXPR const
```
in c++ 03 mode

https://github.com/llvm/llvm-project/pull/109578