google/protobuf/repeated_ptr_field.h

// 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.

// Author: kenton@google.com (Kenton Varda)
//  Based on original Protocol Buffers design by
//  Sanjay Ghemawat, Jeff Dean, and others.
//
// RepeatedField and RepeatedPtrField are used by generated protocol message
// classes to manipulate repeated fields.  These classes are very similar to
// STL's vector, but include a number of optimizations found to be useful
// specifically in the case of Protocol Buffers.  RepeatedPtrField is
// particularly different from STL vector as it manages ownership of the
// pointers that it contains.
//
// This header covers RepeatedPtrField.

// IWYU pragma: private, include "net/proto2/public/repeated_field.h"

#ifndef GOOGLE_PROTOBUF_REPEATED_PTR_FIELD_H__
#define GOOGLE_PROTOBUF_REPEATED_PTR_FIELD_H__

#include <utility>

#ifdef _MSC_VER
// This is required for min/max on VS2013 only.
#include <algorithm>
#endif

#include <iterator>
#include <limits>
#include <string>
#include <type_traits>

#include <google/protobuf/stubs/logging.h>
#include <google/protobuf/stubs/common.h>
#include <google/protobuf/arena.h>
#include <google/protobuf/port.h>
#include <google/protobuf/message_lite.h>


// Must be included last.
#include <google/protobuf/port_def.inc>

#ifdef SWIG
#error "You cannot SWIG proto headers"
#endif

namespace google {
namespace protobuf {

class Message;
class Reflection;

template <typename T>
struct WeakRepeatedPtrField;

namespace internal {

class MergePartialFromCodedStreamHelper;
class SwapFieldHelper;


}  // namespace internal

namespace internal {
template <typename It>
class RepeatedPtrIterator;
template <typename It, typename VoidPtr>
class RepeatedPtrOverPtrsIterator;
}  // namespace internal

namespace internal {

// type-traits helper for RepeatedPtrFieldBase: we only want to invoke
// arena-related "copy if on different arena" behavior if the necessary methods
// exist on the contained type. In particular, we rely on MergeFrom() existing
// as a general proxy for the fact that a copy will work, and we also provide a
// specific override for std::string*.
template <typename T>
struct TypeImplementsMergeBehaviorProbeForMergeFrom {
  typedef char HasMerge;
  typedef long HasNoMerge;

  // We accept either of:
  // - void MergeFrom(const T& other)
  // - bool MergeFrom(const T& other)
  //
  // We mangle these names a bit to avoid compatibility issues in 'unclean'
  // include environments that may have, e.g., "#define test ..." (yes, this
  // exists).
  template <typename U, typename RetType, RetType (U::*)(const U& arg)>
  struct CheckType;
  template <typename U>
  static HasMerge Check(CheckType<U, void, &U::MergeFrom>*);
  template <typename U>
  static HasMerge Check(CheckType<U, bool, &U::MergeFrom>*);
  template <typename U>
  static HasNoMerge Check(...);

  // Resolves to either std::true_type or std::false_type.
  typedef std::integral_constant<bool,
                                 (sizeof(Check<T>(0)) == sizeof(HasMerge))>
      type;
};

template <typename T, typename = void>
struct TypeImplementsMergeBehavior
    : TypeImplementsMergeBehaviorProbeForMergeFrom<T> {};


template <>
struct TypeImplementsMergeBehavior<std::string> {
  typedef std::true_type type;
};

template <typename T>
struct IsMovable
    : std::integral_constant<bool, std::is_move_constructible<T>::value &&
                                       std::is_move_assignable<T>::value> {};

// This is the common base class for RepeatedPtrFields.  It deals only in void*
// pointers.  Users should not use this interface directly.
//
// The methods of this interface correspond to the methods of RepeatedPtrField,
// but may have a template argument called TypeHandler.  Its signature is:
//   class TypeHandler {
//    public:
//     typedef MyType Type;
//     static Type* New();
//     static Type* NewFromPrototype(const Type* prototype,
//                                       Arena* arena);
//     static void Delete(Type*);
//     static void Clear(Type*);
//     static void Merge(const Type& from, Type* to);
//
//     // Only needs to be implemented if SpaceUsedExcludingSelf() is called.
//     static int SpaceUsedLong(const Type&);
//   };
class PROTOBUF_EXPORT RepeatedPtrFieldBase {
 protected:
  constexpr RepeatedPtrFieldBase()
      : arena_(nullptr), current_size_(0), total_size_(0), rep_(nullptr) {}
  explicit RepeatedPtrFieldBase(Arena* arena)
      : arena_(arena), current_size_(0), total_size_(0), rep_(nullptr) {}

  RepeatedPtrFieldBase(const RepeatedPtrFieldBase&) = delete;
  RepeatedPtrFieldBase& operator=(const RepeatedPtrFieldBase&) = delete;

  ~RepeatedPtrFieldBase() {
#ifndef NDEBUG
    // Try to trigger segfault / asan failure in non-opt builds. If arena_
    // lifetime has ended before the destructor.
    if (arena_) (void)arena_->SpaceAllocated();
#endif
  }

  bool empty() const { return current_size_ == 0; }
  int size() const { return current_size_; }
  int Capacity() const { return total_size_; }

  template <typename TypeHandler>
  const typename TypeHandler::Type& at(int index) const {
    GOOGLE_CHECK_GE(index, 0);
    GOOGLE_CHECK_LT(index, current_size_);
    return *cast<TypeHandler>(rep_->elements[index]);
  }

  template <typename TypeHandler>
  typename TypeHandler::Type& at(int index) {
    GOOGLE_CHECK_GE(index, 0);
    GOOGLE_CHECK_LT(index, current_size_);
    return *cast<TypeHandler>(rep_->elements[index]);
  }

  template <typename TypeHandler>
  typename TypeHandler::Type* Mutable(int index) {
    GOOGLE_DCHECK_GE(index, 0);
    GOOGLE_DCHECK_LT(index, current_size_);
    return cast<TypeHandler>(rep_->elements[index]);
  }

  template <typename TypeHandler>
  typename TypeHandler::Type* Add(
      const typename TypeHandler::Type* prototype = nullptr) {
    if (rep_ != nullptr && current_size_ < rep_->allocated_size) {
      return cast<TypeHandler>(rep_->elements[current_size_++]);
    }
    typename TypeHandler::Type* result =
        TypeHandler::NewFromPrototype(prototype, arena_);
    return reinterpret_cast<typename TypeHandler::Type*>(
        AddOutOfLineHelper(result));
  }

  template <
      typename TypeHandler,
      typename std::enable_if<TypeHandler::Movable::value>::type* = nullptr>
  inline void Add(typename TypeHandler::Type&& value) {
    if (rep_ != nullptr && current_size_ < rep_->allocated_size) {
      *cast<TypeHandler>(rep_->elements[current_size_++]) = std::move(value);
      return;
    }
    if (!rep_ || rep_->allocated_size == total_size_) {
      Reserve(total_size_ + 1);
    }
    ++rep_->allocated_size;
    typename TypeHandler::Type* result =
        TypeHandler::New(arena_, std::move(value));
    rep_->elements[current_size_++] = result;
  }

  template <typename TypeHandler>
  void Delete(int index) {
    GOOGLE_DCHECK_GE(index, 0);
    GOOGLE_DCHECK_LT(index, current_size_);
    TypeHandler::Delete(cast<TypeHandler>(rep_->elements[index]), arena_);
  }

  // Must be called from destructor.
  template <typename TypeHandler>
  void Destroy() {
    if (rep_ != nullptr && arena_ == nullptr) {
      int n = rep_->allocated_size;
      void* const* elements = rep_->elements;
      for (int i = 0; i < n; i++) {
        TypeHandler::Delete(cast<TypeHandler>(elements[i]), nullptr);
      }
      const size_t size = total_size_ * sizeof(elements[0]) + kRepHeaderSize;
      internal::SizedDelete(rep_, size);
    }
    rep_ = nullptr;
  }

  bool NeedsDestroy() const { return rep_ != nullptr && arena_ == nullptr; }
  void DestroyProtos();  // implemented in the cc file

 public:
  // The next few methods are public so that they can be called from generated
  // code when implicit weak fields are used, but they should never be called by
  // application code.

  template <typename TypeHandler>
  const typename TypeHandler::Type& Get(int index) const {
    GOOGLE_DCHECK_GE(index, 0);
    GOOGLE_DCHECK_LT(index, current_size_);
    return *cast<TypeHandler>(rep_->elements[index]);
  }

  // Creates and adds an element using the given prototype, without introducing
  // a link-time dependency on the concrete message type. This method is used to
  // implement implicit weak fields. The prototype may be nullptr, in which case
  // an ImplicitWeakMessage will be used as a placeholder.
  MessageLite* AddWeak(const MessageLite* prototype);

  template <typename TypeHandler>
  void Clear() {
    const int n = current_size_;
    GOOGLE_DCHECK_GE(n, 0);
    if (n > 0) {
      void* const* elements = rep_->elements;
      int i = 0;
      do {
        TypeHandler::Clear(cast<TypeHandler>(elements[i++]));
      } while (i < n);
      current_size_ = 0;
    }
  }

  template <typename TypeHandler>
  void MergeFrom(const RepeatedPtrFieldBase& other) {
    // To avoid unnecessary code duplication and reduce binary size, we use a
    // layered approach to implementing MergeFrom(). The toplevel method is
    // templated, so we get a small thunk per concrete message type in the
    // binary. This calls a shared implementation with most of the logic,
    // passing a function pointer to another type-specific piece of code that
    // calls the object-allocate and merge handlers.
    GOOGLE_DCHECK_NE(&other, this);
    if (other.current_size_ == 0) return;
    MergeFromInternal(other,
                      &RepeatedPtrFieldBase::MergeFromInnerLoop<TypeHandler>);
  }

  inline void InternalSwap(RepeatedPtrFieldBase* rhs) {
    GOOGLE_DCHECK(this != rhs);

    // Swap all fields at once.
    auto temp = std::make_tuple(rhs->arena_, rhs->current_size_,
                                rhs->total_size_, rhs->rep_);
    std::tie(rhs->arena_, rhs->current_size_, rhs->total_size_, rhs->rep_) =
        std::make_tuple(arena_, current_size_, total_size_, rep_);
    std::tie(arena_, current_size_, total_size_, rep_) = temp;
  }

 protected:
  template <typename TypeHandler>
  void RemoveLast() {
    GOOGLE_DCHECK_GT(current_size_, 0);
    TypeHandler::Clear(cast<TypeHandler>(rep_->elements[--current_size_]));
  }

  template <typename TypeHandler>
  void CopyFrom(const RepeatedPtrFieldBase& other) {
    if (&other == this) return;
    RepeatedPtrFieldBase::Clear<TypeHandler>();
    RepeatedPtrFieldBase::MergeFrom<TypeHandler>(other);
  }

  void CloseGap(int start, int num);  // implemented in the cc file

  void Reserve(int new_size);  // implemented in the cc file

  template <typename TypeHandler>
  static inline typename TypeHandler::Type* copy(
      typename TypeHandler::Type* value) {
    auto* new_value = TypeHandler::NewFromPrototype(value, nullptr);
    TypeHandler::Merge(*value, new_value);
    return new_value;
  }

  // Used for constructing iterators.
  void* const* raw_data() const { return rep_ ? rep_->elements : nullptr; }
  void** raw_mutable_data() const {
    return rep_ ? const_cast<void**>(rep_->elements) : nullptr;
  }

  template <typename TypeHandler>
  typename TypeHandler::Type** mutable_data() {
    // TODO(kenton):  Breaks C++ aliasing rules.  We should probably remove this
    //   method entirely.
    return reinterpret_cast<typename TypeHandler::Type**>(raw_mutable_data());
  }

  template <typename TypeHandler>
  const typename TypeHandler::Type* const* data() const {
    // TODO(kenton):  Breaks C++ aliasing rules.  We should probably remove this
    //   method entirely.
    return reinterpret_cast<const typename TypeHandler::Type* const*>(
        raw_data());
  }

  template <typename TypeHandler>
  PROTOBUF_NDEBUG_INLINE void Swap(RepeatedPtrFieldBase* other) {
#ifdef PROTOBUF_FORCE_COPY_IN_SWAP
    if (GetArena() != nullptr && GetArena() == other->GetArena())
#else   // PROTOBUF_FORCE_COPY_IN_SWAP
    if (GetArena() == other->GetArena())
#endif  // !PROTOBUF_FORCE_COPY_IN_SWAP
    {
      InternalSwap(other);
    } else {
      SwapFallback<TypeHandler>(other);
    }
  }

  void SwapElements(int index1, int index2) {
    using std::swap;  // enable ADL with fallback
    swap(rep_->elements[index1], rep_->elements[index2]);
  }

  template <typename TypeHandler>
  size_t SpaceUsedExcludingSelfLong() const {
    size_t allocated_bytes = static_cast<size_t>(total_size_) * sizeof(void*);
    if (rep_ != nullptr) {
      for (int i = 0; i < rep_->allocated_size; ++i) {
        allocated_bytes +=
            TypeHandler::SpaceUsedLong(*cast<TypeHandler>(rep_->elements[i]));
      }
      allocated_bytes += kRepHeaderSize;
    }
    return allocated_bytes;
  }

  // Advanced memory management --------------------------------------

  // Like Add(), but if there are no cleared objects to use, returns nullptr.
  template <typename TypeHandler>
  typename TypeHandler::Type* AddFromCleared() {
    if (rep_ != nullptr && current_size_ < rep_->allocated_size) {
      return cast<TypeHandler>(rep_->elements[current_size_++]);
    } else {
      return nullptr;
    }
  }

  template <typename TypeHandler>
  void AddAllocated(typename TypeHandler::Type* value) {
    typename TypeImplementsMergeBehavior<typename TypeHandler::Type>::type t;
    AddAllocatedInternal<TypeHandler>(value, t);
  }

  template <typename TypeHandler>
  void UnsafeArenaAddAllocated(typename TypeHandler::Type* value) {
    // Make room for the new pointer.
    if (!rep_ || current_size_ == total_size_) {
      // The array is completely full with no cleared objects, so grow it.
      Reserve(total_size_ + 1);
      ++rep_->allocated_size;
    } else if (rep_->allocated_size == total_size_) {
      // There is no more space in the pointer array because it contains some
      // cleared objects awaiting reuse.  We don't want to grow the array in
      // this case because otherwise a loop calling AddAllocated() followed by
      // Clear() would leak memory.
      TypeHandler::Delete(cast<TypeHandler>(rep_->elements[current_size_]),
                          arena_);
    } else if (current_size_ < rep_->allocated_size) {
      // We have some cleared objects.  We don't care about their order, so we
      // can just move the first one to the end to make space.
      rep_->elements[rep_->allocated_size] = rep_->elements[current_size_];
      ++rep_->allocated_size;
    } else {
      // There are no cleared objects.
      ++rep_->allocated_size;
    }

    rep_->elements[current_size_++] = value;
  }

  template <typename TypeHandler>
  PROTOBUF_NODISCARD typename TypeHandler::Type* ReleaseLast() {
    typename TypeImplementsMergeBehavior<typename TypeHandler::Type>::type t;
    return ReleaseLastInternal<TypeHandler>(t);
  }

  // Releases and returns the last element, but does not do out-of-arena copy.
  // Instead, just returns the raw pointer to the contained element in the
  // arena.
  template <typename TypeHandler>
  typename TypeHandler::Type* UnsafeArenaReleaseLast() {
    GOOGLE_DCHECK_GT(current_size_, 0);
    typename TypeHandler::Type* result =
        cast<TypeHandler>(rep_->elements[--current_size_]);
    --rep_->allocated_size;
    if (current_size_ < rep_->allocated_size) {
      // There are cleared elements on the end; replace the removed element
      // with the last allocated element.
      rep_->elements[current_size_] = rep_->elements[rep_->allocated_size];
    }
    return result;
  }

  int ClearedCount() const {
    return rep_ ? (rep_->allocated_size - current_size_) : 0;
  }

  template <typename TypeHandler>
  void AddCleared(typename TypeHandler::Type* value) {
    GOOGLE_DCHECK(GetArena() == nullptr) << "AddCleared() can only be used on a "
                                     "RepeatedPtrField not on an arena.";
    GOOGLE_DCHECK(TypeHandler::GetOwningArena(value) == nullptr)
        << "AddCleared() can only accept values not on an arena.";
    if (!rep_ || rep_->allocated_size == total_size_) {
      Reserve(total_size_ + 1);
    }
    rep_->elements[rep_->allocated_size++] = value;
  }

  template <typename TypeHandler>
  PROTOBUF_NODISCARD typename TypeHandler::Type* ReleaseCleared() {
    GOOGLE_DCHECK(GetArena() == nullptr)
        << "ReleaseCleared() can only be used on a RepeatedPtrField not on "
        << "an arena.";
    GOOGLE_DCHECK(GetArena() == nullptr);
    GOOGLE_DCHECK(rep_ != nullptr);
    GOOGLE_DCHECK_GT(rep_->allocated_size, current_size_);
    return cast<TypeHandler>(rep_->elements[--rep_->allocated_size]);
  }

  template <typename TypeHandler>
  void AddAllocatedInternal(typename TypeHandler::Type* value, std::true_type) {
    // AddAllocated version that implements arena-safe copying behavior.
    Arena* element_arena =
        reinterpret_cast<Arena*>(TypeHandler::GetOwningArena(value));
    Arena* arena = GetArena();
    if (arena == element_arena && rep_ && rep_->allocated_size < total_size_) {
      // Fast path: underlying arena representation (tagged pointer) is equal to
      // our arena pointer, and we can add to array without resizing it (at
      // least one slot that is not allocated).
      void** elems = rep_->elements;
      if (current_size_ < rep_->allocated_size) {
        // Make space at [current] by moving first allocated element to end of
        // allocated list.
        elems[rep_->allocated_size] = elems[current_size_];
      }
      elems[current_size_] = value;
      current_size_ = current_size_ + 1;
      rep_->allocated_size = rep_->allocated_size + 1;
    } else {
      AddAllocatedSlowWithCopy<TypeHandler>(value, element_arena, arena);
    }
  }

  template <typename TypeHandler>
  void AddAllocatedInternal(
      // AddAllocated version that does not implement arena-safe copying
      // behavior.
      typename TypeHandler::Type* value, std::false_type) {
    if (rep_ && rep_->allocated_size < total_size_) {
      // Fast path: underlying arena representation (tagged pointer) is equal to
      // our arena pointer, and we can add to array without resizing it (at
      // least one slot that is not allocated).
      void** elems = rep_->elements;
      if (current_size_ < rep_->allocated_size) {
        // Make space at [current] by moving first allocated element to end of
        // allocated list.
        elems[rep_->allocated_size] = elems[current_size_];
      }
      elems[current_size_] = value;
      current_size_ = current_size_ + 1;
      ++rep_->allocated_size;
    } else {
      UnsafeArenaAddAllocated<TypeHandler>(value);
    }
  }

  // Slowpath handles all cases, copying if necessary.
  template <typename TypeHandler>
  PROTOBUF_NOINLINE void AddAllocatedSlowWithCopy(
      // Pass value_arena and my_arena to avoid duplicate virtual call (value)
      // or load (mine).
      typename TypeHandler::Type* value, Arena* value_arena, Arena* my_arena) {
    // Ensure that either the value is in the same arena, or if not, we do the
    // appropriate thing: Own() it (if it's on heap and we're in an arena) or
    // copy it to our arena/heap (otherwise).
    if (my_arena != nullptr && value_arena == nullptr) {
      my_arena->Own(value);
    } else if (my_arena != value_arena) {
      typename TypeHandler::Type* new_value =
          TypeHandler::NewFromPrototype(value, my_arena);
      TypeHandler::Merge(*value, new_value);
      TypeHandler::Delete(value, value_arena);
      value = new_value;
    }

    UnsafeArenaAddAllocated<TypeHandler>(value);
  }

  template <typename TypeHandler>
  typename TypeHandler::Type* ReleaseLastInternal(std::true_type) {
    // ReleaseLast() for types that implement merge/copy behavior.
    // First, release an element.
    typename TypeHandler::Type* result = UnsafeArenaReleaseLast<TypeHandler>();
    // Now perform a copy if we're on an arena.
    Arena* arena = GetArena();

    typename TypeHandler::Type* new_result;
#ifdef PROTOBUF_FORCE_COPY_IN_RELEASE
    new_result = copy<TypeHandler>(result);
    if (arena == nullptr) delete result;
#else   // PROTOBUF_FORCE_COPY_IN_RELEASE
    new_result = (arena == nullptr) ? result : copy<TypeHandler>(result);
#endif  // !PROTOBUF_FORCE_COPY_IN_RELEASE
    return new_result;
  }

  template <typename TypeHandler>
  typename TypeHandler::Type* ReleaseLastInternal(std::false_type) {
    // ReleaseLast() for types that *do not* implement merge/copy behavior --
    // this is the same as UnsafeArenaReleaseLast(). Note that we GOOGLE_DCHECK-fail if
    // we're on an arena, since the user really should implement the copy
    // operation in this case.
    GOOGLE_DCHECK(GetArena() == nullptr)
        << "ReleaseLast() called on a RepeatedPtrField that is on an arena, "
        << "with a type that does not implement MergeFrom. This is unsafe; "
        << "please implement MergeFrom for your type.";
    return UnsafeArenaReleaseLast<TypeHandler>();
  }

  template <typename TypeHandler>
  PROTOBUF_NOINLINE void SwapFallback(RepeatedPtrFieldBase* other) {
#ifdef PROTOBUF_FORCE_COPY_IN_SWAP
    GOOGLE_DCHECK(GetArena() == nullptr || other->GetArena() != GetArena());
#else   // PROTOBUF_FORCE_COPY_IN_SWAP
    GOOGLE_DCHECK(other->GetArena() != GetArena());
#endif  // !PROTOBUF_FORCE_COPY_IN_SWAP

    // Copy semantics in this case. We try to improve efficiency by placing the
    // temporary on |other|'s arena so that messages are copied twice rather
    // than three times.
    RepeatedPtrFieldBase temp(other->GetArena());
    temp.MergeFrom<TypeHandler>(*this);
    this->Clear<TypeHandler>();
    this->MergeFrom<TypeHandler>(*other);
    other->InternalSwap(&temp);
    temp.Destroy<TypeHandler>();  // Frees rep_ if `other` had no arena.
  }

  inline Arena* GetArena() const { return arena_; }

 private:
  template <typename T> friend class Arena::InternalHelper;

  inline Arena* GetOwningArena() const { return arena_; }

  static constexpr int kInitialSize = 0;
  // A few notes on internal representation:
  //
  // We use an indirected approach, with struct Rep, to keep
  // sizeof(RepeatedPtrFieldBase) equivalent to what it was before arena support
  // was added; namely, 3 8-byte machine words on x86-64. An instance of Rep is
  // allocated only when the repeated field is non-empty, and it is a
  // dynamically-sized struct (the header is directly followed by elements[]).
  // We place arena_ and current_size_ directly in the object to avoid cache
  // misses due to the indirection, because these fields are checked frequently.
  // Placing all fields directly in the RepeatedPtrFieldBase instance would cost
  // significant performance for memory-sensitive workloads.
  Arena* arena_;
  int current_size_;
  int total_size_;
  struct Rep {
    int allocated_size;
    // Here we declare a huge array as a way of approximating C's "flexible
    // array member" feature without relying on undefined behavior.
    void* elements[(std::numeric_limits<int>::max() - 2 * sizeof(int)) /
                   sizeof(void*)];
  };
  static constexpr size_t kRepHeaderSize = offsetof(Rep, elements);
  Rep* rep_;

  template <typename TypeHandler>
  static inline typename TypeHandler::Type* cast(void* element) {
    return reinterpret_cast<typename TypeHandler::Type*>(element);
  }
  template <typename TypeHandler>
  static inline const typename TypeHandler::Type* cast(const void* element) {
    return reinterpret_cast<const typename TypeHandler::Type*>(element);
  }

  // Non-templated inner function to avoid code duplication. Takes a function
  // pointer to the type-specific (templated) inner allocate/merge loop.
  void MergeFromInternal(const RepeatedPtrFieldBase& other,
                         void (RepeatedPtrFieldBase::*inner_loop)(void**,
                                                                  void**, int,
                                                                  int)) {
    // Note: wrapper has already guaranteed that other.rep_ != nullptr here.
    int other_size = other.current_size_;
    void** other_elements = other.rep_->elements;
    void** new_elements = InternalExtend(other_size);
    int allocated_elems = rep_->allocated_size - current_size_;
    (this->*inner_loop)(new_elements, other_elements, other_size,
                        allocated_elems);
    current_size_ += other_size;
    if (rep_->allocated_size < current_size_) {
      rep_->allocated_size = current_size_;
    }
  }

  // Merges other_elems to our_elems.
  template <typename TypeHandler>
  PROTOBUF_NOINLINE void MergeFromInnerLoop(void** our_elems,
                                            void** other_elems, int length,
                                            int already_allocated) {
    if (already_allocated < length) {
      Arena* arena = GetArena();
      typename TypeHandler::Type* elem_prototype =
          reinterpret_cast<typename TypeHandler::Type*>(other_elems[0]);
      for (int i = already_allocated; i < length; i++) {
        // Allocate a new empty element that we'll merge into below
        typename TypeHandler::Type* new_elem =
            TypeHandler::NewFromPrototype(elem_prototype, arena);
        our_elems[i] = new_elem;
      }
    }
    // Main loop that does the actual merging
    for (int i = 0; i < length; i++) {
      // Already allocated: use existing element.
      typename TypeHandler::Type* other_elem =
          reinterpret_cast<typename TypeHandler::Type*>(other_elems[i]);
      typename TypeHandler::Type* new_elem =
          reinterpret_cast<typename TypeHandler::Type*>(our_elems[i]);
      TypeHandler::Merge(*other_elem, new_elem);
    }
  }

  // Internal helper: extends array space if necessary to contain
  // |extend_amount| more elements, and returns a pointer to the element
  // immediately following the old list of elements.  This interface factors out
  // common behavior from Reserve() and MergeFrom() to reduce code size.
  // |extend_amount| must be > 0.
  void** InternalExtend(int extend_amount);

  // Internal helper for Add: adds "obj" as the next element in the
  // array, including potentially resizing the array with Reserve if
  // needed
  void* AddOutOfLineHelper(void* obj);

  // The reflection implementation needs to call protected methods directly,
  // reinterpreting pointers as being to Message instead of a specific Message
  // subclass.
  friend class ::PROTOBUF_NAMESPACE_ID::Reflection;
  friend class ::PROTOBUF_NAMESPACE_ID::internal::SwapFieldHelper;

  // ExtensionSet stores repeated message extensions as
  // RepeatedPtrField<MessageLite>, but non-lite ExtensionSets need to implement
  // SpaceUsedLong(), and thus need to call SpaceUsedExcludingSelfLong()
  // reinterpreting MessageLite as Message.  ExtensionSet also needs to make use
  // of AddFromCleared(), which is not part of the public interface.
  friend class ExtensionSet;

  // The MapFieldBase implementation needs to call protected methods directly,
  // reinterpreting pointers as being to Message instead of a specific Message
  // subclass.
  friend class MapFieldBase;
  friend class MapFieldBaseStub;

  // The table-driven MergePartialFromCodedStream implementation needs to
  // operate on RepeatedPtrField<MessageLite>.
  friend class MergePartialFromCodedStreamHelper;
  friend class AccessorHelper;
  template <typename T>
  friend struct google::protobuf::WeakRepeatedPtrField;
  friend class internal::TcParser;  // TODO(jorg): Remove this friend.
};

template <typename GenericType>
class GenericTypeHandler {
 public:
  typedef GenericType Type;
  using Movable = IsMovable<GenericType>;

  static inline GenericType* New(Arena* arena) {
    return Arena::CreateMaybeMessage<Type>(arena);
  }
  static inline GenericType* New(Arena* arena, GenericType&& value) {
    return Arena::Create<GenericType>(arena, std::move(value));
  }
  static inline GenericType* NewFromPrototype(const GenericType* prototype,
                                              Arena* arena = nullptr) {
    return New(arena);
  }
  static inline void Delete(GenericType* value, Arena* arena) {
    if (arena == nullptr) {
      delete value;
    }
  }
  static inline Arena* GetOwningArena(GenericType* value) {
    return Arena::GetOwningArena<Type>(value);
  }

  static inline void Clear(GenericType* value) { value->Clear(); }
  static void Merge(const GenericType& from, GenericType* to);
  static inline size_t SpaceUsedLong(const GenericType& value) {
    return value.SpaceUsedLong();
  }
};

// NewFromPrototypeHelper() is not defined inline here, as we will need to do a
// virtual function dispatch anyways to go from Message* to call New/Merge. (The
// additional helper is needed as a workaround for MSVC.)
MessageLite* NewFromPrototypeHelper(const MessageLite* prototype, Arena* arena);

template <>
inline MessageLite* GenericTypeHandler<MessageLite>::NewFromPrototype(
    const MessageLite* prototype, Arena* arena) {
  return NewFromPrototypeHelper(prototype, arena);
}
template <>
inline Arena* GenericTypeHandler<MessageLite>::GetOwningArena(
    MessageLite* value) {
  return value->GetOwningArena();
}

template <typename GenericType>
PROTOBUF_NOINLINE inline void GenericTypeHandler<GenericType>::Merge(
    const GenericType& from, GenericType* to) {
  to->MergeFrom(from);
}
template <>
void GenericTypeHandler<MessageLite>::Merge(const MessageLite& from,
                                            MessageLite* to);

template <>
inline void GenericTypeHandler<std::string>::Clear(std::string* value) {
  value->clear();
}
template <>
void GenericTypeHandler<std::string>::Merge(const std::string& from,
                                            std::string* to);

// Message specialization bodies defined in message.cc. This split is necessary
// to allow proto2-lite (which includes this header) to be independent of
// Message.
template <>
PROTOBUF_EXPORT Message* GenericTypeHandler<Message>::NewFromPrototype(
    const Message* prototype, Arena* arena);
template <>
PROTOBUF_EXPORT Arena* GenericTypeHandler<Message>::GetOwningArena(
    Message* value);

class StringTypeHandler {
 public:
  typedef std::string Type;
  using Movable = IsMovable<Type>;

  static inline std::string* New(Arena* arena) {
    return Arena::Create<std::string>(arena);
  }
  static inline std::string* New(Arena* arena, std::string&& value) {
    return Arena::Create<std::string>(arena, std::move(value));
  }
  static inline std::string* NewFromPrototype(const std::string*,
                                              Arena* arena) {
    return New(arena);
  }
  static inline Arena* GetOwningArena(std::string*) { return nullptr; }
  static inline void Delete(std::string* value, Arena* arena) {
    if (arena == nullptr) {
      delete value;
    }
  }
  static inline void Clear(std::string* value) { value->clear(); }
  static inline void Merge(const std::string& from, std::string* to) {
    *to = from;
  }
  static size_t SpaceUsedLong(const std::string& value) {
    return sizeof(value) + StringSpaceUsedExcludingSelfLong(value);
  }
};

}  // namespace internal

// RepeatedPtrField is like RepeatedField, but used for repeated strings or
// Messages.
template <typename Element>
class RepeatedPtrField final : private internal::RepeatedPtrFieldBase {

 public:
  constexpr RepeatedPtrField();
  explicit RepeatedPtrField(Arena* arena);

  RepeatedPtrField(const RepeatedPtrField& other);

  template <typename Iter,
            typename = typename std::enable_if<std::is_constructible<
                Element, decltype(*std::declval<Iter>())>::value>::type>
  RepeatedPtrField(Iter begin, Iter end);

  ~RepeatedPtrField();

  RepeatedPtrField& operator=(const RepeatedPtrField& other);

  RepeatedPtrField(RepeatedPtrField&& other) noexcept;
  RepeatedPtrField& operator=(RepeatedPtrField&& other) noexcept;

  bool empty() const;
  int size() const;

  const Element& Get(int index) const;
  Element* Mutable(int index);
  Element* Add();
  void Add(Element&& value);
  // Append elements in the range [begin, end) after reserving
  // the appropriate number of elements.
  template <typename Iter>
  void Add(Iter begin, Iter end);

  const Element& operator[](int index) const { return Get(index); }
  Element& operator[](int index) { return *Mutable(index); }

  const Element& at(int index) const;
  Element& at(int index);

  // Removes the last element in the array.
  // Ownership of the element is retained by the array.
  void RemoveLast();

  // Deletes elements with indices in the range [start .. start+num-1].
  // Caution: moves all elements with indices [start+num .. ].
  // Calling this routine inside a loop can cause quadratic behavior.
  void DeleteSubrange(int start, int num);

  PROTOBUF_ATTRIBUTE_REINITIALIZES void Clear();
  void MergeFrom(const RepeatedPtrField& other);
  PROTOBUF_ATTRIBUTE_REINITIALIZES void CopyFrom(const RepeatedPtrField& other);

  // Replaces the contents with RepeatedPtrField(begin, end).
  template <typename Iter>
  PROTOBUF_ATTRIBUTE_REINITIALIZES void Assign(Iter begin, Iter end);

  // Reserves space to expand the field to at least the given size.  This only
  // resizes the pointer array; it doesn't allocate any objects.  If the
  // array is grown, it will always be at least doubled in size.
  void Reserve(int new_size);

  int Capacity() const;

  // Gets the underlying array.  This pointer is possibly invalidated by
  // any add or remove operation.
  //
  // This API is deprecated. Instead of directly working with element array,
  // use APIs in repeated_field_util.h; e.g. sorting, etc.
  PROTOBUF_DEPRECATED_MSG("Use APIs in repeated_field_util.h")
  Element** mutable_data();
  const Element* const* data() const;

  // Swaps entire contents with "other". If they are on separate arenas, then
  // copies data.
  void Swap(RepeatedPtrField* other);

  // Swaps entire contents with "other". Caller should guarantee that either
  // both fields are on the same arena or both are on the heap. Swapping between
  // different arenas with this function is disallowed and is caught via
  // GOOGLE_DCHECK.
  void UnsafeArenaSwap(RepeatedPtrField* other);

  // Swaps two elements.
  void SwapElements(int index1, int index2);

  // STL-like iterator support
  typedef internal::RepeatedPtrIterator<Element> iterator;
  typedef internal::RepeatedPtrIterator<const Element> const_iterator;
  typedef Element value_type;
  typedef value_type& reference;
  typedef const value_type& const_reference;
  typedef value_type* pointer;
  typedef const value_type* const_pointer;
  typedef int size_type;
  typedef ptrdiff_t difference_type;

  iterator begin();
  const_iterator begin() const;
  const_iterator cbegin() const;
  iterator end();
  const_iterator end() const;
  const_iterator cend() const;

  // Reverse iterator support
  typedef std::reverse_iterator<const_iterator> const_reverse_iterator;
  typedef std::reverse_iterator<iterator> reverse_iterator;
  reverse_iterator rbegin() { return reverse_iterator(end()); }
  const_reverse_iterator rbegin() const {
    return const_reverse_iterator(end());
  }
  reverse_iterator rend() { return reverse_iterator(begin()); }
  const_reverse_iterator rend() const {
    return const_reverse_iterator(begin());
  }

  // Custom STL-like iterator that iterates over and returns the underlying
  // pointers to Element rather than Element itself.
  typedef internal::RepeatedPtrOverPtrsIterator<Element*, void*>
      pointer_iterator;
  typedef internal::RepeatedPtrOverPtrsIterator<const Element* const,
                                                const void* const>
      const_pointer_iterator;
  pointer_iterator pointer_begin();
  const_pointer_iterator pointer_begin() const;
  pointer_iterator pointer_end();
  const_pointer_iterator pointer_end() const;

  // Returns (an estimate of) the number of bytes used by the repeated field,
  // excluding sizeof(*this).
  size_t SpaceUsedExcludingSelfLong() const;

  int SpaceUsedExcludingSelf() const {
    return internal::ToIntSize(SpaceUsedExcludingSelfLong());
  }

  // Advanced memory management --------------------------------------
  // When hardcore memory management becomes necessary -- as it sometimes
  // does here at Google -- the following methods may be useful.

  // Adds an already-allocated object, passing ownership to the
  // RepeatedPtrField.
  //
  // Note that some special behavior occurs with respect to arenas:
  //
  //   (i) if this field holds submessages, the new submessage will be copied if
  //   the original is in an arena and this RepeatedPtrField is either in a
  //   different arena, or on the heap.
  //   (ii) if this field holds strings, the passed-in string *must* be
  //   heap-allocated, not arena-allocated. There is no way to dynamically check
  //   this at runtime, so User Beware.
  void AddAllocated(Element* value);

  // Removes and returns the last element, passing ownership to the caller.
  // Requires:  size() > 0
  //
  // If this RepeatedPtrField is on an arena, an object copy is required to pass
  // ownership back to the user (for compatible semantics). Use
  // UnsafeArenaReleaseLast() if this behavior is undesired.
  PROTOBUF_NODISCARD Element* ReleaseLast();

  // Adds an already-allocated object, skipping arena-ownership checks. The user
  // must guarantee that the given object is in the same arena as this
  // RepeatedPtrField.
  // It is also useful in legacy code that uses temporary ownership to avoid
  // copies. Example:
  //   RepeatedPtrField<T> temp_field;
  //   temp_field.UnsafeArenaAddAllocated(new T);
  //   ... // Do something with temp_field
  //   temp_field.UnsafeArenaExtractSubrange(0, temp_field.size(), nullptr);
  // If you put temp_field on the arena this fails, because the ownership
  // transfers to the arena at the "AddAllocated" call and is not released
  // anymore, causing a double delete. UnsafeArenaAddAllocated prevents this.
  void UnsafeArenaAddAllocated(Element* value);

  // Removes and returns the last element.  Unlike ReleaseLast, the returned
  // pointer is always to the original object.  This may be in an arena, in
  // which case it would have the arena's lifetime.
  // Requires: current_size_ > 0
  Element* UnsafeArenaReleaseLast();

  // Extracts elements with indices in the range "[start .. start+num-1]".
  // The caller assumes ownership of the extracted elements and is responsible
  // for deleting them when they are no longer needed.
  // If "elements" is non-nullptr, then pointers to the extracted elements
  // are stored in "elements[0 .. num-1]" for the convenience of the caller.
  // If "elements" is nullptr, then the caller must use some other mechanism
  // to perform any further operations (like deletion) on these elements.
  // Caution: implementation also moves elements with indices [start+num ..].
  // Calling this routine inside a loop can cause quadratic behavior.
  //
  // Memory copying behavior is identical to ReleaseLast(), described above: if
  // this RepeatedPtrField is on an arena, an object copy is performed for each
  // returned element, so that all returned element pointers are to
  // heap-allocated copies. If this copy is not desired, the user should call
  // UnsafeArenaExtractSubrange().
  void ExtractSubrange(int start, int num, Element** elements);

  // Identical to ExtractSubrange() described above, except that no object
  // copies are ever performed. Instead, the raw object pointers are returned.
  // Thus, if on an arena, the returned objects must not be freed, because they
  // will not be heap-allocated objects.
  void UnsafeArenaExtractSubrange(int start, int num, Element** elements);

  // When elements are removed by calls to RemoveLast() or Clear(), they
  // are not actually freed.  Instead, they are cleared and kept so that
  // they can be reused later.  This can save lots of CPU time when
  // repeatedly reusing a protocol message for similar purposes.
  //
  // Hardcore programs may choose to manipulate these cleared objects
  // to better optimize memory management using the following routines.

  // Gets the number of cleared objects that are currently being kept
  // around for reuse.
  int ClearedCount() const;
#ifndef PROTOBUF_FUTURE_BREAKING_CHANGES
  // Adds an element to the pool of cleared objects, passing ownership to
  // the RepeatedPtrField.  The element must be cleared prior to calling
  // this method.
  //
  // This method cannot be called when either the repeated field or |value| is
  // on an arena; both cases will trigger a GOOGLE_DCHECK-failure.
  void AddCleared(Element* value);
  // Removes and returns a single element from the cleared pool, passing
  // ownership to the caller.  The element is guaranteed to be cleared.
  // Requires:  ClearedCount() > 0
  //
  // This method cannot be called when the repeated field is on an arena; doing
  // so will trigger a GOOGLE_DCHECK-failure.
  PROTOBUF_NODISCARD Element* ReleaseCleared();
#endif  // !PROTOBUF_FUTURE_BREAKING_CHANGES

  // Removes the element referenced by position.
  //
  // Returns an iterator to the element immediately following the removed
  // element.
  //
  // Invalidates all iterators at or after the removed element, including end().
  iterator erase(const_iterator position);

  // Removes the elements in the range [first, last).
  //
  // Returns an iterator to the element immediately following the removed range.
  //
  // Invalidates all iterators at or after the removed range, including end().
  iterator erase(const_iterator first, const_iterator last);

  // Gets the arena on which this RepeatedPtrField stores its elements.
  inline Arena* GetArena() const;

  // For internal use only.
  //
  // This is public due to it being called by generated code.
  void InternalSwap(RepeatedPtrField* other) {
    internal::RepeatedPtrFieldBase::InternalSwap(other);
  }

 private:
  // Note:  RepeatedPtrField SHOULD NOT be subclassed by users.
  class TypeHandler;

  // Implementations for ExtractSubrange(). The copying behavior must be
  // included only if the type supports the necessary operations (e.g.,
  // MergeFrom()), so we must resolve this at compile time. ExtractSubrange()
  // uses SFINAE to choose one of the below implementations.
  void ExtractSubrangeInternal(int start, int num, Element** elements,
                               std::true_type);
  void ExtractSubrangeInternal(int start, int num, Element** elements,
                               std::false_type);

  friend class Arena;

  template <typename T>
  friend struct WeakRepeatedPtrField;

  typedef void InternalArenaConstructable_;

};

// -------------------------------------------------------------------

template <typename Element>
class RepeatedPtrField<Element>::TypeHandler
    : public internal::GenericTypeHandler<Element> {};

template <>
class RepeatedPtrField<std::string>::TypeHandler
    : public internal::StringTypeHandler {};

template <typename Element>
constexpr RepeatedPtrField<Element>::RepeatedPtrField()
    : RepeatedPtrFieldBase() {}

template <typename Element>
inline RepeatedPtrField<Element>::RepeatedPtrField(Arena* arena)
    : RepeatedPtrFieldBase(arena) {}

template <typename Element>
inline RepeatedPtrField<Element>::RepeatedPtrField(
    const RepeatedPtrField& other)
    : RepeatedPtrFieldBase() {
  MergeFrom(other);
}

template <typename Element>
template <typename Iter, typename>
inline RepeatedPtrField<Element>::RepeatedPtrField(Iter begin, Iter end) {
  Add(begin, end);
}

template <typename Element>
RepeatedPtrField<Element>::~RepeatedPtrField() {
#ifdef __cpp_if_constexpr
  if constexpr (std::is_base_of<MessageLite, Element>::value) {
#else
  if (std::is_base_of<MessageLite, Element>::value) {
#endif
    if (NeedsDestroy()) DestroyProtos();
  } else {
    Destroy<TypeHandler>();
  }
}

template <typename Element>
inline RepeatedPtrField<Element>& RepeatedPtrField<Element>::operator=(
    const RepeatedPtrField& other) {
  if (this != &other) CopyFrom(other);
  return *this;
}

template <typename Element>
inline RepeatedPtrField<Element>::RepeatedPtrField(
    RepeatedPtrField&& other) noexcept
    : RepeatedPtrField() {
#ifdef PROTOBUF_FORCE_COPY_IN_MOVE
  CopyFrom(other);
#else   // PROTOBUF_FORCE_COPY_IN_MOVE
  // We don't just call Swap(&other) here because it would perform 3 copies if
  // other is on an arena. This field can't be on an arena because arena
  // construction always uses the Arena* accepting constructor.
  if (other.GetArena()) {
    CopyFrom(other);
  } else {
    InternalSwap(&other);
  }
#endif  // !PROTOBUF_FORCE_COPY_IN_MOVE
}

template <typename Element>
inline RepeatedPtrField<Element>& RepeatedPtrField<Element>::operator=(
    RepeatedPtrField&& other) noexcept {
  // We don't just call Swap(&other) here because it would perform 3 copies if
  // the two fields are on different arenas.
  if (this != &other) {
    if (GetArena() != other.GetArena()
#ifdef PROTOBUF_FORCE_COPY_IN_MOVE
        || GetArena() == nullptr
#endif  // !PROTOBUF_FORCE_COPY_IN_MOVE
    ) {
      CopyFrom(other);
    } else {
      InternalSwap(&other);
    }
  }
  return *this;
}

template <typename Element>
inline bool RepeatedPtrField<Element>::empty() const {
  return RepeatedPtrFieldBase::empty();
}

template <typename Element>
inline int RepeatedPtrField<Element>::size() const {
  return RepeatedPtrFieldBase::size();
}

template <typename Element>
inline const Element& RepeatedPtrField<Element>::Get(int index) const {
  return RepeatedPtrFieldBase::Get<TypeHandler>(index);
}

template <typename Element>
inline const Element& RepeatedPtrField<Element>::at(int index) const {
  return RepeatedPtrFieldBase::at<TypeHandler>(index);
}

template <typename Element>
inline Element& RepeatedPtrField<Element>::at(int index) {
  return RepeatedPtrFieldBase::at<TypeHandler>(index);
}


template <typename Element>
inline Element* RepeatedPtrField<Element>::Mutable(int index) {
  return RepeatedPtrFieldBase::Mutable<TypeHandler>(index);
}

template <typename Element>
inline Element* RepeatedPtrField<Element>::Add() {
  return RepeatedPtrFieldBase::Add<TypeHandler>();
}

template <typename Element>
inline void RepeatedPtrField<Element>::Add(Element&& value) {
  RepeatedPtrFieldBase::Add<TypeHandler>(std::move(value));
}

template <typename Element>
template <typename Iter>
inline void RepeatedPtrField<Element>::Add(Iter begin, Iter end) {
  if (std::is_base_of<
          std::forward_iterator_tag,
          typename std::iterator_traits<Iter>::iterator_category>::value) {
    int reserve = std::distance(begin, end);
    Reserve(size() + reserve);
  }
  for (; begin != end; ++begin) {
    *Add() = *begin;
  }
}

template <typename Element>
inline void RepeatedPtrField<Element>::RemoveLast() {
  RepeatedPtrFieldBase::RemoveLast<TypeHandler>();
}

template <typename Element>
inline void RepeatedPtrField<Element>::DeleteSubrange(int start, int num) {
  GOOGLE_DCHECK_GE(start, 0);
  GOOGLE_DCHECK_GE(num, 0);
  GOOGLE_DCHECK_LE(start + num, size());
  for (int i = 0; i < num; ++i) {
    RepeatedPtrFieldBase::Delete<TypeHandler>(start + i);
  }
  UnsafeArenaExtractSubrange(start, num, nullptr);
}

template <typename Element>
inline void RepeatedPtrField<Element>::ExtractSubrange(int start, int num,
                                                       Element** elements) {
  typename internal::TypeImplementsMergeBehavior<
      typename TypeHandler::Type>::type t;
  ExtractSubrangeInternal(start, num, elements, t);
}

// ExtractSubrange() implementation for types that implement merge/copy
// behavior.
template <typename Element>
inline void RepeatedPtrField<Element>::ExtractSubrangeInternal(
    int start, int num, Element** elements, std::true_type) {
  GOOGLE_DCHECK_GE(start, 0);
  GOOGLE_DCHECK_GE(num, 0);
  GOOGLE_DCHECK_LE(start + num, size());

  if (num == 0) return;

  GOOGLE_DCHECK_NE(elements, nullptr)
      << "Releasing elements without transferring ownership is an unsafe "
         "operation.  Use UnsafeArenaExtractSubrange.";
  if (elements == nullptr) {
    CloseGap(start, num);
    return;
  }

  Arena* arena = GetArena();
#ifdef PROTOBUF_FORCE_COPY_IN_RELEASE
  // Always copy.
  for (int i = 0; i < num; ++i) {
    elements[i] = copy<TypeHandler>(
        RepeatedPtrFieldBase::Mutable<TypeHandler>(i + start));
  }
  if (arena == nullptr) {
    for (int i = 0; i < num; ++i) {
      delete RepeatedPtrFieldBase::Mutable<TypeHandler>(i + start);
    }
  }
#else   // PROTOBUF_FORCE_COPY_IN_RELEASE
  // If we're on an arena, we perform a copy for each element so that the
  // returned elements are heap-allocated. Otherwise, just forward it.
  if (arena != nullptr) {
    for (int i = 0; i < num; ++i) {
      elements[i] = copy<TypeHandler>(
          RepeatedPtrFieldBase::Mutable<TypeHandler>(i + start));
    }
  } else {
    for (int i = 0; i < num; ++i) {
      elements[i] = RepeatedPtrFieldBase::Mutable<TypeHandler>(i + start);
    }
  }
#endif  // !PROTOBUF_FORCE_COPY_IN_RELEASE
  CloseGap(start, num);
}

// ExtractSubrange() implementation for types that do not implement merge/copy
// behavior.
template <typename Element>
inline void RepeatedPtrField<Element>::ExtractSubrangeInternal(
    int start, int num, Element** elements, std::false_type) {
  // This case is identical to UnsafeArenaExtractSubrange(). However, since
  // ExtractSubrange() must return heap-allocated objects by contract, and we
  // cannot fulfill this contract if we are an on arena, we must GOOGLE_DCHECK() that
  // we are not on an arena.
  GOOGLE_DCHECK(GetArena() == nullptr)
      << "ExtractSubrange() when arena is non-nullptr is only supported when "
      << "the Element type supplies a MergeFrom() operation to make copies.";
  UnsafeArenaExtractSubrange(start, num, elements);
}

template <typename Element>
inline void RepeatedPtrField<Element>::UnsafeArenaExtractSubrange(
    int start, int num, Element** elements) {
  GOOGLE_DCHECK_GE(start, 0);
  GOOGLE_DCHECK_GE(num, 0);
  GOOGLE_DCHECK_LE(start + num, size());

  if (num > 0) {
    // Save the values of the removed elements if requested.
    if (elements != nullptr) {
      for (int i = 0; i < num; ++i) {
        elements[i] = RepeatedPtrFieldBase::Mutable<TypeHandler>(i + start);
      }
    }
    CloseGap(start, num);
  }
}

template <typename Element>
inline void RepeatedPtrField<Element>::Clear() {
  RepeatedPtrFieldBase::Clear<TypeHandler>();
}

template <typename Element>
inline void RepeatedPtrField<Element>::MergeFrom(
    const RepeatedPtrField& other) {
  RepeatedPtrFieldBase::MergeFrom<TypeHandler>(other);
}

template <typename Element>
inline void RepeatedPtrField<Element>::CopyFrom(const RepeatedPtrField& other) {
  RepeatedPtrFieldBase::CopyFrom<TypeHandler>(other);
}

template <typename Element>
template <typename Iter>
inline void RepeatedPtrField<Element>::Assign(Iter begin, Iter end) {
  Clear();
  Add(begin, end);
}

template <typename Element>
inline typename RepeatedPtrField<Element>::iterator
RepeatedPtrField<Element>::erase(const_iterator position) {
  return erase(position, position + 1);
}

template <typename Element>
inline typename RepeatedPtrField<Element>::iterator
RepeatedPtrField<Element>::erase(const_iterator first, const_iterator last) {
  size_type pos_offset = std::distance(cbegin(), first);
  size_type last_offset = std::distance(cbegin(), last);
  DeleteSubrange(pos_offset, last_offset - pos_offset);
  return begin() + pos_offset;
}

template <typename Element>
inline Element** RepeatedPtrField<Element>::mutable_data() {
  return RepeatedPtrFieldBase::mutable_data<TypeHandler>();
}

template <typename Element>
inline const Element* const* RepeatedPtrField<Element>::data() const {
  return RepeatedPtrFieldBase::data<TypeHandler>();
}

template <typename Element>
inline void RepeatedPtrField<Element>::Swap(RepeatedPtrField* other) {
  if (this == other) return;
  RepeatedPtrFieldBase::Swap<TypeHandler>(other);
}

template <typename Element>
inline void RepeatedPtrField<Element>::UnsafeArenaSwap(
    RepeatedPtrField* other) {
  if (this == other) return;
  GOOGLE_DCHECK_EQ(GetArena(), other->GetArena());
  RepeatedPtrFieldBase::InternalSwap(other);
}

template <typename Element>
inline void RepeatedPtrField<Element>::SwapElements(int index1, int index2) {
  RepeatedPtrFieldBase::SwapElements(index1, index2);
}

template <typename Element>
inline Arena* RepeatedPtrField<Element>::GetArena() const {
  return RepeatedPtrFieldBase::GetArena();
}

template <typename Element>
inline size_t RepeatedPtrField<Element>::SpaceUsedExcludingSelfLong() const {
  return RepeatedPtrFieldBase::SpaceUsedExcludingSelfLong<TypeHandler>();
}

template <typename Element>
inline void RepeatedPtrField<Element>::AddAllocated(Element* value) {
  RepeatedPtrFieldBase::AddAllocated<TypeHandler>(value);
}

template <typename Element>
inline void RepeatedPtrField<Element>::UnsafeArenaAddAllocated(Element* value) {
  RepeatedPtrFieldBase::UnsafeArenaAddAllocated<TypeHandler>(value);
}

template <typename Element>
inline Element* RepeatedPtrField<Element>::ReleaseLast() {
  return RepeatedPtrFieldBase::ReleaseLast<TypeHandler>();
}

template <typename Element>
inline Element* RepeatedPtrField<Element>::UnsafeArenaReleaseLast() {
  return RepeatedPtrFieldBase::UnsafeArenaReleaseLast<TypeHandler>();
}

template <typename Element>
inline int RepeatedPtrField<Element>::ClearedCount() const {
  return RepeatedPtrFieldBase::ClearedCount();
}

#ifndef PROTOBUF_FUTURE_BREAKING_CHANGES
template <typename Element>
inline void RepeatedPtrField<Element>::AddCleared(Element* value) {
  return RepeatedPtrFieldBase::AddCleared<TypeHandler>(value);
}

template <typename Element>
inline Element* RepeatedPtrField<Element>::ReleaseCleared() {
  return RepeatedPtrFieldBase::ReleaseCleared<TypeHandler>();
}
#endif  // !PROTOBUF_FUTURE_BREAKING_CHANGES

template <typename Element>
inline void RepeatedPtrField<Element>::Reserve(int new_size) {
  return RepeatedPtrFieldBase::Reserve(new_size);
}

template <typename Element>
inline int RepeatedPtrField<Element>::Capacity() const {
  return RepeatedPtrFieldBase::Capacity();
}

// -------------------------------------------------------------------

namespace internal {

// STL-like iterator implementation for RepeatedPtrField.  You should not
// refer to this class directly; use RepeatedPtrField<T>::iterator instead.
//
// The iterator for RepeatedPtrField<T>, RepeatedPtrIterator<T>, is
// very similar to iterator_ptr<T**> in util/gtl/iterator_adaptors.h,
// but adds random-access operators and is modified to wrap a void** base
// iterator (since RepeatedPtrField stores its array as a void* array and
// casting void** to T** would violate C++ aliasing rules).
//
// This code based on net/proto/proto-array-internal.h by Jeffrey Yasskin
// (jyasskin@google.com).
template <typename Element>
class RepeatedPtrIterator {
 public:
  using iterator = RepeatedPtrIterator<Element>;
  using iterator_category = std::random_access_iterator_tag;
  using value_type = typename std::remove_const<Element>::type;
  using difference_type = std::ptrdiff_t;
  using pointer = Element*;
  using reference = Element&;

  RepeatedPtrIterator() : it_(nullptr) {}
  explicit RepeatedPtrIterator(void* const* it) : it_(it) {}

  // Allows "upcasting" from RepeatedPtrIterator<T**> to
  // RepeatedPtrIterator<const T*const*>.
  template <typename OtherElement,
            typename std::enable_if<std::is_convertible<
                OtherElement*, pointer>::value>::type* = nullptr>
  RepeatedPtrIterator(const RepeatedPtrIterator<OtherElement>& other)
      : it_(other.it_) {}

  // dereferenceable
  reference operator*() const { return *reinterpret_cast<Element*>(*it_); }
  pointer operator->() const { return &(operator*()); }

  // {inc,dec}rementable
  iterator& operator++() {
    ++it_;
    return *this;
  }
  iterator operator++(int) { return iterator(it_++); }
  iterator& operator--() {
    --it_;
    return *this;
  }
  iterator operator--(int) { return iterator(it_--); }

  // equality_comparable
  friend bool operator==(const iterator& x, const iterator& y) {
    return x.it_ == y.it_;
  }
  friend bool operator!=(const iterator& x, const iterator& y) {
    return x.it_ != y.it_;
  }

  // less_than_comparable
  friend bool operator<(const iterator& x, const iterator& y) {
    return x.it_ < y.it_;
  }
  friend bool operator<=(const iterator& x, const iterator& y) {
    return x.it_ <= y.it_;
  }
  friend bool operator>(const iterator& x, const iterator& y) {
    return x.it_ > y.it_;
  }
  friend bool operator>=(const iterator& x, const iterator& y) {
    return x.it_ >= y.it_;
  }

  // addable, subtractable
  iterator& operator+=(difference_type d) {
    it_ += d;
    return *this;
  }
  friend iterator operator+(iterator it, const difference_type d) {
    it += d;
    return it;
  }
  friend iterator operator+(const difference_type d, iterator it) {
    it += d;
    return it;
  }
  iterator& operator-=(difference_type d) {
    it_ -= d;
    return *this;
  }
  friend iterator operator-(iterator it, difference_type d) {
    it -= d;
    return it;
  }

  // indexable
  reference operator[](difference_type d) const { return *(*this + d); }

  // random access iterator
  friend difference_type operator-(iterator it1, iterator it2) {
    return it1.it_ - it2.it_;
  }

 private:
  template <typename OtherElement>
  friend class RepeatedPtrIterator;

  // The internal iterator.
  void* const* it_;
};

// Provides an iterator that operates on pointers to the underlying objects
// rather than the objects themselves as RepeatedPtrIterator does.
// Consider using this when working with stl algorithms that change
// the array.
// The VoidPtr template parameter holds the type-agnostic pointer value
// referenced by the iterator.  It should either be "void *" for a mutable
// iterator, or "const void* const" for a constant iterator.
template <typename Element, typename VoidPtr>
class RepeatedPtrOverPtrsIterator {
 public:
  using iterator = RepeatedPtrOverPtrsIterator<Element, VoidPtr>;
  using iterator_category = std::random_access_iterator_tag;
  using value_type = typename std::remove_const<Element>::type;
  using difference_type = std::ptrdiff_t;
  using pointer = Element*;
  using reference = Element&;

  RepeatedPtrOverPtrsIterator() : it_(nullptr) {}
  explicit RepeatedPtrOverPtrsIterator(VoidPtr* it) : it_(it) {}

  // Allows "upcasting" from RepeatedPtrOverPtrsIterator<T**> to
  // RepeatedPtrOverPtrsIterator<const T*const*>.
  template <
      typename OtherElement, typename OtherVoidPtr,
      typename std::enable_if<
          std::is_convertible<OtherElement*, pointer>::value &&
          std::is_convertible<OtherVoidPtr*, VoidPtr>::value>::type* = nullptr>
  RepeatedPtrOverPtrsIterator(
      const RepeatedPtrOverPtrsIterator<OtherElement, OtherVoidPtr>& other)
      : it_(other.it_) {}

  // dereferenceable
  reference operator*() const { return *reinterpret_cast<Element*>(it_); }
  pointer operator->() const { return &(operator*()); }

  // {inc,dec}rementable
  iterator& operator++() {
    ++it_;
    return *this;
  }
  iterator operator++(int) { return iterator(it_++); }
  iterator& operator--() {
    --it_;
    return *this;
  }
  iterator operator--(int) { return iterator(it_--); }

  // equality_comparable
  friend bool operator==(const iterator& x, const iterator& y) {
    return x.it_ == y.it_;
  }
  friend bool operator!=(const iterator& x, const iterator& y) {
    return x.it_ != y.it_;
  }

  // less_than_comparable
  friend bool operator<(const iterator& x, const iterator& y) {
    return x.it_ < y.it_;
  }
  friend bool operator<=(const iterator& x, const iterator& y) {
    return x.it_ <= y.it_;
  }
  friend bool operator>(const iterator& x, const iterator& y) {
    return x.it_ > y.it_;
  }
  friend bool operator>=(const iterator& x, const iterator& y) {
    return x.it_ >= y.it_;
  }

  // addable, subtractable
  iterator& operator+=(difference_type d) {
    it_ += d;
    return *this;
  }
  friend iterator operator+(iterator it, difference_type d) {
    it += d;
    return it;
  }
  friend iterator operator+(difference_type d, iterator it) {
    it += d;
    return it;
  }
  iterator& operator-=(difference_type d) {
    it_ -= d;
    return *this;
  }
  friend iterator operator-(iterator it, difference_type d) {
    it -= d;
    return it;
  }

  // indexable
  reference operator[](difference_type d) const { return *(*this + d); }

  // random access iterator
  friend difference_type operator-(iterator it1, iterator it2) {
    return it1.it_ - it2.it_;
  }

 private:
  template <typename OtherElement, typename OtherVoidPtr>
  friend class RepeatedPtrOverPtrsIterator;

  // The internal iterator.
  VoidPtr* it_;
};

}  // namespace internal

template <typename Element>
inline typename RepeatedPtrField<Element>::iterator
RepeatedPtrField<Element>::begin() {
  return iterator(raw_data());
}
template <typename Element>
inline typename RepeatedPtrField<Element>::const_iterator
RepeatedPtrField<Element>::begin() const {
  return iterator(raw_data());
}
template <typename Element>
inline typename RepeatedPtrField<Element>::const_iterator
RepeatedPtrField<Element>::cbegin() const {
  return begin();
}
template <typename Element>
inline typename RepeatedPtrField<Element>::iterator
RepeatedPtrField<Element>::end() {
  return iterator(raw_data() + size());
}
template <typename Element>
inline typename RepeatedPtrField<Element>::const_iterator
RepeatedPtrField<Element>::end() const {
  return iterator(raw_data() + size());
}
template <typename Element>
inline typename RepeatedPtrField<Element>::const_iterator
RepeatedPtrField<Element>::cend() const {
  return end();
}

template <typename Element>
inline typename RepeatedPtrField<Element>::pointer_iterator
RepeatedPtrField<Element>::pointer_begin() {
  return pointer_iterator(raw_mutable_data());
}
template <typename Element>
inline typename RepeatedPtrField<Element>::const_pointer_iterator
RepeatedPtrField<Element>::pointer_begin() const {
  return const_pointer_iterator(const_cast<const void* const*>(raw_data()));
}
template <typename Element>
inline typename RepeatedPtrField<Element>::pointer_iterator
RepeatedPtrField<Element>::pointer_end() {
  return pointer_iterator(raw_mutable_data() + size());
}
template <typename Element>
inline typename RepeatedPtrField<Element>::const_pointer_iterator
RepeatedPtrField<Element>::pointer_end() const {
  return const_pointer_iterator(
      const_cast<const void* const*>(raw_data() + size()));
}

// Iterators and helper functions that follow the spirit of the STL
// std::back_insert_iterator and std::back_inserter but are tailor-made
// for RepeatedField and RepeatedPtrField. Typical usage would be:
//
//   std::copy(some_sequence.begin(), some_sequence.end(),
//             RepeatedFieldBackInserter(proto.mutable_sequence()));
//
// Ported by johannes from util/gtl/proto-array-iterators.h

namespace internal {

// A back inserter for RepeatedPtrField objects.
template <typename T>
class RepeatedPtrFieldBackInsertIterator {
 public:
  using iterator_category = std::output_iterator_tag;
  using value_type = T;
  using pointer = void;
  using reference = void;
  using difference_type = std::ptrdiff_t;

  RepeatedPtrFieldBackInsertIterator(RepeatedPtrField<T>* const mutable_field)
      : field_(mutable_field) {}
  RepeatedPtrFieldBackInsertIterator<T>& operator=(const T& value) {
    *field_->Add() = value;
    return *this;
  }
  RepeatedPtrFieldBackInsertIterator<T>& operator=(
      const T* const ptr_to_value) {
    *field_->Add() = *ptr_to_value;
    return *this;
  }
  RepeatedPtrFieldBackInsertIterator<T>& operator=(T&& value) {
    *field_->Add() = std::move(value);
    return *this;
  }
  RepeatedPtrFieldBackInsertIterator<T>& operator*() { return *this; }
  RepeatedPtrFieldBackInsertIterator<T>& operator++() { return *this; }
  RepeatedPtrFieldBackInsertIterator<T>& operator++(int /* unused */) {
    return *this;
  }

 private:
  RepeatedPtrField<T>* field_;
};

// A back inserter for RepeatedPtrFields that inserts by transferring ownership
// of a pointer.
template <typename T>
class AllocatedRepeatedPtrFieldBackInsertIterator {
 public:
  using iterator_category = std::output_iterator_tag;
  using value_type = T;
  using pointer = void;
  using reference = void;
  using difference_type = std::ptrdiff_t;

  explicit AllocatedRepeatedPtrFieldBackInsertIterator(
      RepeatedPtrField<T>* const mutable_field)
      : field_(mutable_field) {}
  AllocatedRepeatedPtrFieldBackInsertIterator<T>& operator=(
      T* const ptr_to_value) {
    field_->AddAllocated(ptr_to_value);
    return *this;
  }
  AllocatedRepeatedPtrFieldBackInsertIterator<T>& operator*() { return *this; }
  AllocatedRepeatedPtrFieldBackInsertIterator<T>& operator++() { return *this; }
  AllocatedRepeatedPtrFieldBackInsertIterator<T>& operator++(int /* unused */) {
    return *this;
  }

 private:
  RepeatedPtrField<T>* field_;
};

// Almost identical to AllocatedRepeatedPtrFieldBackInsertIterator. This one
// uses the UnsafeArenaAddAllocated instead.
template <typename T>
class UnsafeArenaAllocatedRepeatedPtrFieldBackInsertIterator {
 public:
  using iterator_category = std::output_iterator_tag;
  using value_type = T;
  using pointer = void;
  using reference = void;
  using difference_type = std::ptrdiff_t;

  explicit UnsafeArenaAllocatedRepeatedPtrFieldBackInsertIterator(
      RepeatedPtrField<T>* const mutable_field)
      : field_(mutable_field) {}
  UnsafeArenaAllocatedRepeatedPtrFieldBackInsertIterator<T>& operator=(
      T const* const ptr_to_value) {
    field_->UnsafeArenaAddAllocated(const_cast<T*>(ptr_to_value));
    return *this;
  }
  UnsafeArenaAllocatedRepeatedPtrFieldBackInsertIterator<T>& operator*() {
    return *this;
  }
  UnsafeArenaAllocatedRepeatedPtrFieldBackInsertIterator<T>& operator++() {
    return *this;
  }
  UnsafeArenaAllocatedRepeatedPtrFieldBackInsertIterator<T>& operator++(
      int /* unused */) {
    return *this;
  }

 private:
  RepeatedPtrField<T>* field_;
};

}  // namespace internal

// Provides a back insert iterator for RepeatedPtrField instances,
// similar to std::back_inserter().
template <typename T>
internal::RepeatedPtrFieldBackInsertIterator<T> RepeatedPtrFieldBackInserter(
    RepeatedPtrField<T>* const mutable_field) {
  return internal::RepeatedPtrFieldBackInsertIterator<T>(mutable_field);
}

// Special back insert iterator for RepeatedPtrField instances, just in
// case someone wants to write generic template code that can access both
// RepeatedFields and RepeatedPtrFields using a common name.
template <typename T>
internal::RepeatedPtrFieldBackInsertIterator<T> RepeatedFieldBackInserter(
    RepeatedPtrField<T>* const mutable_field) {
  return internal::RepeatedPtrFieldBackInsertIterator<T>(mutable_field);
}

// Provides a back insert iterator for RepeatedPtrField instances
// similar to std::back_inserter() which transfers the ownership while
// copying elements.
template <typename T>
internal::AllocatedRepeatedPtrFieldBackInsertIterator<T>
AllocatedRepeatedPtrFieldBackInserter(
    RepeatedPtrField<T>* const mutable_field) {
  return internal::AllocatedRepeatedPtrFieldBackInsertIterator<T>(
      mutable_field);
}

// Similar to AllocatedRepeatedPtrFieldBackInserter, using
// UnsafeArenaAddAllocated instead of AddAllocated.
// This is slightly faster if that matters. It is also useful in legacy code
// that uses temporary ownership to avoid copies. Example:
//   RepeatedPtrField<T> temp_field;
//   temp_field.UnsafeArenaAddAllocated(new T);
//   ... // Do something with temp_field
//   temp_field.UnsafeArenaExtractSubrange(0, temp_field.size(), nullptr);
// Putting temp_field on the arena fails because the ownership transfers to the
// arena at the "AddAllocated" call and is not released anymore causing a
// double delete. This function uses UnsafeArenaAddAllocated to prevent this.
template <typename T>
internal::UnsafeArenaAllocatedRepeatedPtrFieldBackInsertIterator<T>
UnsafeArenaAllocatedRepeatedPtrFieldBackInserter(
    RepeatedPtrField<T>* const mutable_field) {
  return internal::UnsafeArenaAllocatedRepeatedPtrFieldBackInsertIterator<T>(
      mutable_field);
}

extern template class PROTOBUF_EXPORT_TEMPLATE_DECLARE
    RepeatedPtrField<std::string>;

}  // namespace protobuf
}  // namespace google

#include <google/protobuf/port_undef.inc>

#endif  // GOOGLE_PROTOBUF_REPEATED_PTR_FIELD_H__