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diff --git a/include/google/protobuf/explicitly_constructed.h b/include/google/protobuf/explicitly_constructed.h
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+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#ifndef GOOGLE_PROTOBUF_EXPLICITLY_CONSTRUCTED_H__
+#define GOOGLE_PROTOBUF_EXPLICITLY_CONSTRUCTED_H__
+
+#include <stdint.h>
+
+#include <utility>
+
+#include <google/protobuf/stubs/logging.h>
+#include <google/protobuf/stubs/common.h>
+
+// clang-format off
+#include <google/protobuf/port_def.inc>
+// clang-format on
+
+namespace google {
+namespace protobuf {
+namespace internal {
+
+// Wraps a variable whose constructor and destructor are explicitly
+// called. It is particularly useful for a global variable, without its
+// constructor and destructor run on start and end of the program lifetime.
+// This circumvents the initial construction order fiasco, while keeping
+// the address of the empty string a compile time constant.
+//
+// Pay special attention to the initialization state of the object.
+// 1. The object is "uninitialized" to begin with.
+// 2. Call Construct() or DefaultConstruct() only if the object is
+//    uninitialized. After the call, the object becomes "initialized".
+// 3. Call get() and get_mutable() only if the object is initialized.
+// 4. Call Destruct() only if the object is initialized.
+//    After the call, the object becomes uninitialized.
+template <typename T, size_t min_align = 1>
+class ExplicitlyConstructed {
+ public:
+  void DefaultConstruct() { new (&union_) T(); }
+
+  template <typename... Args>
+  void Construct(Args&&... args) {
+    new (&union_) T(std::forward<Args>(args)...);
+  }
+
+  void Destruct() { get_mutable()->~T(); }
+
+  constexpr const T& get() const { return reinterpret_cast<const T&>(union_); }
+  T* get_mutable() { return reinterpret_cast<T*>(&union_); }
+
+ private:
+  union AlignedUnion {
+    alignas(min_align > alignof(T) ? min_align
+                                   : alignof(T)) char space[sizeof(T)];
+    int64_t align_to_int64;
+    void* align_to_ptr;
+  } union_;
+};
+
+// ArenaStringPtr compatible explicitly constructed string type.
+// This empty string type is aligned with a minimum alignment of 8 bytes
+// which is the minimum requirement of ArenaStringPtr
+using ExplicitlyConstructedArenaString = ExplicitlyConstructed<std::string, 8>;
+
+}  // namespace internal
+}  // namespace protobuf
+}  // namespace google
+
+#include <google/protobuf/port_undef.inc>
+
+#endif  // GOOGLE_PROTOBUF_EXPLICITLY_CONSTRUCTED_H__