flatbuffers.h

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/*
 * Copyright 2014 Google Inc. All rights reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef FLATBUFFERS_H_
#define FLATBUFFERS_H_

#include "behaviortree_cpp_v3/flatbuffers/base.h"
#include "behaviortree_cpp_v3/flatbuffers/stl_emulation.h"

#ifndef FLATBUFFERS_CPP98_STL
#include <functional>
#endif

#if defined(FLATBUFFERS_NAN_DEFAULTS)
#include <cmath>
#endif

namespace flatbuffers
{
// Generic 'operator==' with conditional specialisations.
// T e - new value of a scalar field.
// T def - default of scalar (is known at compile-time).
template <typename T>
inline bool IsTheSameAs(T e, T def)
{
  return e == def;
}

#if defined(FLATBUFFERS_NAN_DEFAULTS) && defined(FLATBUFFERS_HAS_NEW_STRTOD) &&          \
    (FLATBUFFERS_HAS_NEW_STRTOD > 0)
// Like `operator==(e, def)` with weak NaN if T=(float|double).
template <typename T>
inline bool IsFloatTheSameAs(T e, T def)
{
  return (e == def) || ((def != def) && (e != e));
}
template <>
inline bool IsTheSameAs<float>(float e, float def)
{
  return IsFloatTheSameAs(e, def);
}
template <>
inline bool IsTheSameAs<double>(double e, double def)
{
  return IsFloatTheSameAs(e, def);
}
#endif

// Check 'v' is out of closed range [low; high].
// Workaround for GCC warning [-Werror=type-limits]:
// comparison is always true due to limited range of data type.
template <typename T>
inline bool IsOutRange(const T& v, const T& low, const T& high)
{
  return (v < low) || (high < v);
}

// Check 'v' is in closed range [low; high].
template <typename T>
inline bool IsInRange(const T& v, const T& low, const T& high)
{
  return !IsOutRange(v, low, high);
}

// Wrapper for uoffset_t to allow safe template specialization.
// Value is allowed to be 0 to indicate a null object (see e.g. AddOffset).
template <typename T>
struct Offset
{
  uoffset_t o;
  Offset() : o(0)
  {}
  Offset(uoffset_t _o) : o(_o)
  {}
  Offset<void> Union() const
  {
    return Offset<void>(o);
  }
  bool IsNull() const
  {
    return !o;
  }
};

inline void EndianCheck()
{
  int endiantest = 1;
  // If this fails, see FLATBUFFERS_LITTLEENDIAN above.
  FLATBUFFERS_ASSERT(*reinterpret_cast<char*>(&endiantest) == FLATBUFFERS_LITTLEENDIAN);
  (void)endiantest;
}

template <typename T>
FLATBUFFERS_CONSTEXPR size_t AlignOf()
{
  // clang-format off
  #ifdef _MSC_VER
    return __alignof(T);
  #else
    #ifndef alignof
      return __alignof__(T);
    #else
      return alignof(T);
    #endif
  #endif
  // clang-format on
}

// When we read serialized data from memory, in the case of most scalars,
// we want to just read T, but in the case of Offset, we want to actually
// perform the indirection and return a pointer.
// The template specialization below does just that.
// It is wrapped in a struct since function templates can't overload on the
// return type like this.
// The typedef is for the convenience of callers of this function
// (avoiding the need for a trailing return decltype)
template <typename T>
struct IndirectHelper
{
  typedef T return_type;
  typedef T mutable_return_type;
  static const size_t element_stride = sizeof(T);
  static return_type Read(const uint8_t* p, uoffset_t i)
  {
    return EndianScalar((reinterpret_cast<const T*>(p))[i]);
  }
};
template <typename T>
struct IndirectHelper<Offset<T>>
{
  typedef const T* return_type;
  typedef T* mutable_return_type;
  static const size_t element_stride = sizeof(uoffset_t);
  static return_type Read(const uint8_t* p, uoffset_t i)
  {
    p += i * sizeof(uoffset_t);
    return reinterpret_cast<return_type>(p + ReadScalar<uoffset_t>(p));
  }
};
template <typename T>
struct IndirectHelper<const T*>
{
  typedef const T* return_type;
  typedef T* mutable_return_type;
  static const size_t element_stride = sizeof(T);
  static return_type Read(const uint8_t* p, uoffset_t i)
  {
    return reinterpret_cast<const T*>(p + i * sizeof(T));
  }
};

// An STL compatible iterator implementation for Vector below, effectively
// calling Get() for every element.
template <typename T, typename IT>
struct VectorIterator
{
  typedef std::random_access_iterator_tag iterator_category;
  typedef IT value_type;
  typedef ptrdiff_t difference_type;
  typedef IT* pointer;
  typedef IT& reference;

  VectorIterator(const uint8_t* data, uoffset_t i) :
    data_(data + IndirectHelper<T>::element_stride * i)
  {}
  VectorIterator(const VectorIterator& other) : data_(other.data_)
  {}
  VectorIterator() : data_(nullptr)
  {}

  VectorIterator& operator=(const VectorIterator& other)
  {
    data_ = other.data_;
    return *this;
  }

  // clang-format off
  #if !defined(FLATBUFFERS_CPP98_STL)
  VectorIterator &operator=(VectorIterator &&other) {
    data_ = other.data_;
    return *this;
  }
  #endif  // !defined(FLATBUFFERS_CPP98_STL)
  // clang-format on

  bool operator==(const VectorIterator& other) const
  {
    return data_ == other.data_;
  }

  bool operator<(const VectorIterator& other) const
  {
    return data_ < other.data_;
  }

  bool operator!=(const VectorIterator& other) const
  {
    return data_ != other.data_;
  }

  difference_type operator-(const VectorIterator& other) const
  {
    return (data_ - other.data_) / IndirectHelper<T>::element_stride;
  }

  IT operator*() const
  {
    return IndirectHelper<T>::Read(data_, 0);
  }

  IT operator->() const
  {
    return IndirectHelper<T>::Read(data_, 0);
  }

  VectorIterator& operator++()
  {
    data_ += IndirectHelper<T>::element_stride;
    return *this;
  }

  VectorIterator operator++(int)
  {
    VectorIterator temp(data_, 0);
    data_ += IndirectHelper<T>::element_stride;
    return temp;
  }

  VectorIterator operator+(const uoffset_t& offset) const
  {
    return VectorIterator(data_ + offset * IndirectHelper<T>::element_stride, 0);
  }

  VectorIterator& operator+=(const uoffset_t& offset)
  {
    data_ += offset * IndirectHelper<T>::element_stride;
    return *this;
  }

  VectorIterator& operator--()
  {
    data_ -= IndirectHelper<T>::element_stride;
    return *this;
  }

  VectorIterator operator--(int)
  {
    VectorIterator temp(data_, 0);
    data_ -= IndirectHelper<T>::element_stride;
    return temp;
  }

  VectorIterator operator-(const uoffset_t& offset) const
  {
    return VectorIterator(data_ - offset * IndirectHelper<T>::element_stride, 0);
  }

  VectorIterator& operator-=(const uoffset_t& offset)
  {
    data_ -= offset * IndirectHelper<T>::element_stride;
    return *this;
  }

private:
  const uint8_t* data_;
};

template <typename Iterator>
struct VectorReverseIterator : public std::reverse_iterator<Iterator>
{
  explicit VectorReverseIterator(Iterator iter) : std::reverse_iterator<Iterator>(iter)
  {}

  typename Iterator::value_type operator*() const
  {
    return *(std::reverse_iterator<Iterator>::current);
  }

  typename Iterator::value_type operator->() const
  {
    return *(std::reverse_iterator<Iterator>::current);
  }
};

struct String;

// This is used as a helper type for accessing vectors.
// Vector::data() assumes the vector elements start after the length field.
template <typename T>
class Vector
{
public:
  typedef VectorIterator<T, typename IndirectHelper<T>::mutable_return_type> iterator;
  typedef VectorIterator<T, typename IndirectHelper<T>::return_type> const_iterator;
  typedef VectorReverseIterator<iterator> reverse_iterator;
  typedef VectorReverseIterator<const_iterator> const_reverse_iterator;

  uoffset_t size() const
  {
    return EndianScalar(length_);
  }

  // Deprecated: use size(). Here for backwards compatibility.
  FLATBUFFERS_ATTRIBUTE(deprecated("use size() instead"))
  uoffset_t Length() const
  {
    return size();
  }

  typedef typename IndirectHelper<T>::return_type return_type;
  typedef typename IndirectHelper<T>::mutable_return_type mutable_return_type;
  typedef return_type value_type;

  return_type Get(uoffset_t i) const
  {
    FLATBUFFERS_ASSERT(i < size());
    return IndirectHelper<T>::Read(Data(), i);
  }

  return_type operator[](uoffset_t i) const
  {
    return Get(i);
  }

  // If this is a Vector of enums, T will be its storage type, not the enum
  // type. This function makes it convenient to retrieve value with enum
  // type E.
  template <typename E>
  E GetEnum(uoffset_t i) const
  {
    return static_cast<E>(Get(i));
  }

  // If this a vector of unions, this does the cast for you. There's no check
  // to make sure this is the right type!
  template <typename U>
  const U* GetAs(uoffset_t i) const
  {
    return reinterpret_cast<const U*>(Get(i));
  }

  // If this a vector of unions, this does the cast for you. There's no check
  // to make sure this is actually a string!
  const String* GetAsString(uoffset_t i) const
  {
    return reinterpret_cast<const String*>(Get(i));
  }

  const void* GetStructFromOffset(size_t o) const
  {
    return reinterpret_cast<const void*>(Data() + o);
  }

  iterator begin()
  {
    return iterator(Data(), 0);
  }
  const_iterator begin() const
  {
    return const_iterator(Data(), 0);
  }

  iterator end()
  {
    return iterator(Data(), size());
  }
  const_iterator end() const
  {
    return const_iterator(Data(), size());
  }

  reverse_iterator rbegin()
  {
    return reverse_iterator(end() - 1);
  }
  const_reverse_iterator rbegin() const
  {
    return const_reverse_iterator(end() - 1);
  }

  reverse_iterator rend()
  {
    return reverse_iterator(begin() - 1);
  }
  const_reverse_iterator rend() const
  {
    return const_reverse_iterator(begin() - 1);
  }

  const_iterator cbegin() const
  {
    return begin();
  }

  const_iterator cend() const
  {
    return end();
  }

  const_reverse_iterator crbegin() const
  {
    return rbegin();
  }

  const_reverse_iterator crend() const
  {
    return rend();
  }

  // Change elements if you have a non-const pointer to this object.
  // Scalars only. See reflection.h, and the documentation.
  void Mutate(uoffset_t i, const T& val)
  {
    FLATBUFFERS_ASSERT(i < size());
    WriteScalar(data() + i, val);
  }

  // Change an element of a vector of tables (or strings).
  // "val" points to the new table/string, as you can obtain from
  // e.g. reflection::AddFlatBuffer().
  void MutateOffset(uoffset_t i, const uint8_t* val)
  {
    FLATBUFFERS_ASSERT(i < size());
    static_assert(sizeof(T) == sizeof(uoffset_t), "Unrelated types");
    WriteScalar(data() + i,
                static_cast<uoffset_t>(val - (Data() + i * sizeof(uoffset_t))));
  }

  // Get a mutable pointer to tables/strings inside this vector.
  mutable_return_type GetMutableObject(uoffset_t i) const
  {
    FLATBUFFERS_ASSERT(i < size());
    return const_cast<mutable_return_type>(IndirectHelper<T>::Read(Data(), i));
  }

  // The raw data in little endian format. Use with care.
  const uint8_t* Data() const
  {
    return reinterpret_cast<const uint8_t*>(&length_ + 1);
  }

  uint8_t* Data()
  {
    return reinterpret_cast<uint8_t*>(&length_ + 1);
  }

  // Similarly, but typed, much like std::vector::data
  const T* data() const
  {
    return reinterpret_cast<const T*>(Data());
  }
  T* data()
  {
    return reinterpret_cast<T*>(Data());
  }

  template <typename K>
  return_type LookupByKey(K key) const
  {
    void* search_result = std::bsearch(&key, Data(), size(),
                                       IndirectHelper<T>::element_stride, KeyCompare<K>);

    if (!search_result)
    {
      return nullptr;   // Key not found.
    }

    const uint8_t* element = reinterpret_cast<const uint8_t*>(search_result);

    return IndirectHelper<T>::Read(element, 0);
  }

protected:
  // This class is only used to access pre-existing data. Don't ever
  // try to construct these manually.
  Vector();

  uoffset_t length_;

private:
  // This class is a pointer. Copying will therefore create an invalid object.
  // Private and unimplemented copy constructor.
  Vector(const Vector&);
  Vector& operator=(const Vector&);

  template <typename K>
  static int KeyCompare(const void* ap, const void* bp)
  {
    const K* key = reinterpret_cast<const K*>(ap);
    const uint8_t* data = reinterpret_cast<const uint8_t*>(bp);
    auto table = IndirectHelper<T>::Read(data, 0);

    // std::bsearch compares with the operands transposed, so we negate the
    // result here.
    return -table->KeyCompareWithValue(*key);
  }
};

// Represent a vector much like the template above, but in this case we
// don't know what the element types are (used with reflection.h).
class VectorOfAny
{
public:
  uoffset_t size() const
  {
    return EndianScalar(length_);
  }

  const uint8_t* Data() const
  {
    return reinterpret_cast<const uint8_t*>(&length_ + 1);
  }
  uint8_t* Data()
  {
    return reinterpret_cast<uint8_t*>(&length_ + 1);
  }

protected:
  VectorOfAny();

  uoffset_t length_;

private:
  VectorOfAny(const VectorOfAny&);
  VectorOfAny& operator=(const VectorOfAny&);
};

#ifndef FLATBUFFERS_CPP98_STL
template <typename T, typename U>
Vector<Offset<T>>* VectorCast(Vector<Offset<U>>* ptr)
{
  static_assert(std::is_base_of<T, U>::value, "Unrelated types");
  return reinterpret_cast<Vector<Offset<T>>*>(ptr);
}

template <typename T, typename U>
const Vector<Offset<T>>* VectorCast(const Vector<Offset<U>>* ptr)
{
  static_assert(std::is_base_of<T, U>::value, "Unrelated types");
  return reinterpret_cast<const Vector<Offset<T>>*>(ptr);
}
#endif

// Convenient helper function to get the length of any vector, regardless
// of whether it is null or not (the field is not set).
template <typename T>
static inline size_t VectorLength(const Vector<T>* v)
{
  return v ? v->size() : 0;
}

// This is used as a helper type for accessing arrays.
template <typename T, uint16_t length>
class Array
{
  typedef typename flatbuffers::integral_constant<bool, flatbuffers::is_scalar<T>::value>
      scalar_tag;
  typedef typename flatbuffers::conditional<scalar_tag::value, T, const T*>::type
      IndirectHelperType;

public:
  typedef uint16_t size_type;
  typedef typename IndirectHelper<IndirectHelperType>::return_type return_type;
  typedef VectorIterator<T, return_type> const_iterator;
  typedef VectorReverseIterator<const_iterator> const_reverse_iterator;

  FLATBUFFERS_CONSTEXPR uint16_t size() const
  {
    return length;
  }

  return_type Get(uoffset_t i) const
  {
    FLATBUFFERS_ASSERT(i < size());
    return IndirectHelper<IndirectHelperType>::Read(Data(), i);
  }

  return_type operator[](uoffset_t i) const
  {
    return Get(i);
  }

  // If this is a Vector of enums, T will be its storage type, not the enum
  // type. This function makes it convenient to retrieve value with enum
  // type E.
  template <typename E>
  E GetEnum(uoffset_t i) const
  {
    return static_cast<E>(Get(i));
  }

  const_iterator begin() const
  {
    return const_iterator(Data(), 0);
  }
  const_iterator end() const
  {
    return const_iterator(Data(), size());
  }

  const_reverse_iterator rbegin() const
  {
    return const_reverse_iterator(end());
  }
  const_reverse_iterator rend() const
  {
    return const_reverse_iterator(end());
  }

  const_iterator cbegin() const
  {
    return begin();
  }
  const_iterator cend() const
  {
    return end();
  }

  const_reverse_iterator crbegin() const
  {
    return rbegin();
  }
  const_reverse_iterator crend() const
  {
    return rend();
  }

  // Get a mutable pointer to elements inside this array.
  // This method used to mutate arrays of structs followed by a @p Mutate
  // operation. For primitive types use @p Mutate directly.
  // @warning Assignments and reads to/from the dereferenced pointer are not
  //  automatically converted to the correct endianness.
  typename flatbuffers::conditional<scalar_tag::value, void, T*>::type
  GetMutablePointer(uoffset_t i) const
  {
    FLATBUFFERS_ASSERT(i < size());
    return const_cast<T*>(&data()[i]);
  }

  // Change elements if you have a non-const pointer to this object.
  void Mutate(uoffset_t i, const T& val)
  {
    MutateImpl(scalar_tag(), i, val);
  }

  // The raw data in little endian format. Use with care.
  const uint8_t* Data() const
  {
    return data_;
  }

  uint8_t* Data()
  {
    return data_;
  }

  // Similarly, but typed, much like std::vector::data
  const T* data() const
  {
    return reinterpret_cast<const T*>(Data());
  }
  T* data()
  {
    return reinterpret_cast<T*>(Data());
  }

  // Copy data from a span with endian conversion.
  // If this Array and the span overlap, the behavior is undefined.
  void CopyFromSpan(flatbuffers::span<const T, length> src)
  {
    const auto p1 = reinterpret_cast<const uint8_t*>(src.data());
    const auto p2 = Data();
    FLATBUFFERS_ASSERT(!(p1 >= p2 && p1 < (p2 + length)) &&
                       !(p2 >= p1 && p2 < (p1 + length)));
    (void)p1;
    (void)p2;

    CopyFromSpanImpl(
        flatbuffers::integral_constant < bool,
        !scalar_tag::value || sizeof(T) == 1 || FLATBUFFERS_LITTLEENDIAN > (), src);
  }

protected:
  void MutateImpl(flatbuffers::integral_constant<bool, true>, uoffset_t i, const T& val)
  {
    FLATBUFFERS_ASSERT(i < size());
    WriteScalar(data() + i, val);
  }

  void MutateImpl(flatbuffers::integral_constant<bool, false>, uoffset_t i, const T& val)
  {
    *(GetMutablePointer(i)) = val;
  }

  void CopyFromSpanImpl(flatbuffers::integral_constant<bool, true>,
                        flatbuffers::span<const T, length> src)
  {
    // Use std::memcpy() instead of std::copy() to avoid preformance degradation
    // due to aliasing if T is char or unsigned char.
    // The size is known at compile time, so memcpy would be inlined.
    std::memcpy(data(), src.data(), length * sizeof(T));
  }

  // Copy data from flatbuffers::span with endian conversion.
  void CopyFromSpanImpl(flatbuffers::integral_constant<bool, false>,
                        flatbuffers::span<const T, length> src)
  {
    for (size_type k = 0; k < length; k++)
    {
      Mutate(k, src[k]);
    }
  }

  // This class is only used to access pre-existing data. Don't ever
  // try to construct these manually.
  // 'constexpr' allows us to use 'size()' at compile time.
  // @note Must not use 'FLATBUFFERS_CONSTEXPR' here, as const is not allowed on
  //  a constructor.
#if defined(__cpp_constexpr)
  constexpr Array();
#else
  Array();
#endif

  uint8_t data_[length * sizeof(T)];

private:
  // This class is a pointer. Copying will therefore create an invalid object.
  // Private and unimplemented copy constructor.
  Array(const Array&);
  Array& operator=(const Array&);
};

// Specialization for Array[struct] with access using Offset<void> pointer.
// This specialization used by idl_gen_text.cpp.
template <typename T, uint16_t length>
class Array<Offset<T>, length>
{
  static_assert(flatbuffers::is_same<T, void>::value, "unexpected type T");

public:
  typedef const void* return_type;

  const uint8_t* Data() const
  {
    return data_;
  }

  // Make idl_gen_text.cpp::PrintContainer happy.
  return_type operator[](uoffset_t) const
  {
    FLATBUFFERS_ASSERT(false);
    return nullptr;
  }

private:
  // This class is only used to access pre-existing data.
  Array();
  Array(const Array&);
  Array& operator=(const Array&);

  uint8_t data_[1];
};

// Cast a raw T[length] to a raw flatbuffers::Array<T, length>
// without endian conversion. Use with care.
template <typename T, uint16_t length>
Array<T, length>& CastToArray(T (&arr)[length])
{
  return *reinterpret_cast<Array<T, length>*>(arr);
}

template <typename T, uint16_t length>
const Array<T, length>& CastToArray(const T (&arr)[length])
{
  return *reinterpret_cast<const Array<T, length>*>(arr);
}

template <typename E, typename T, uint16_t length>
Array<E, length>& CastToArrayOfEnum(T (&arr)[length])
{
  static_assert(sizeof(E) == sizeof(T), "invalid enum type E");
  return *reinterpret_cast<Array<E, length>*>(arr);
}

template <typename E, typename T, uint16_t length>
const Array<E, length>& CastToArrayOfEnum(const T (&arr)[length])
{
  static_assert(sizeof(E) == sizeof(T), "invalid enum type E");
  return *reinterpret_cast<const Array<E, length>*>(arr);
}

// Lexicographically compare two strings (possibly containing nulls), and
// return true if the first is less than the second.
static inline bool StringLessThan(const char* a_data, uoffset_t a_size,
                                  const char* b_data, uoffset_t b_size)
{
  const auto cmp = memcmp(a_data, b_data, (std::min)(a_size, b_size));
  return cmp == 0 ? a_size < b_size : cmp < 0;
}

struct String : public Vector<char>
{
  const char* c_str() const
  {
    return reinterpret_cast<const char*>(Data());
  }
  std::string str() const
  {
    return std::string(c_str(), size());
  }

  // clang-format off
  #ifdef FLATBUFFERS_HAS_STRING_VIEW
  flatbuffers::string_view string_view() const {
    return flatbuffers::string_view(c_str(), size());
  }
  #endif // FLATBUFFERS_HAS_STRING_VIEW
  // clang-format on

  bool operator<(const String& o) const
  {
    return StringLessThan(this->data(), this->size(), o.data(), o.size());
  }
};

// Convenience function to get std::string from a String returning an empty
// string on null pointer.
static inline std::string GetString(const String* str)
{
  return str ? str->str() : "";
}

// Convenience function to get char* from a String returning an empty string on
// null pointer.
static inline const char* GetCstring(const String* str)
{
  return str ? str->c_str() : "";
}

#ifdef FLATBUFFERS_HAS_STRING_VIEW
// Convenience function to get string_view from a String returning an empty
// string_view on null pointer.
static inline flatbuffers::string_view GetStringView(const String* str)
{
  return str ? str->string_view() : flatbuffers::string_view();
}
#endif   // FLATBUFFERS_HAS_STRING_VIEW

// Allocator interface. This is flatbuffers-specific and meant only for
// `vector_downward` usage.
class Allocator
{
public:
  virtual ~Allocator()
  {}

  // Allocate `size` bytes of memory.
  virtual uint8_t* allocate(size_t size) = 0;

  // Deallocate `size` bytes of memory at `p` allocated by this allocator.
  virtual void deallocate(uint8_t* p, size_t size) = 0;

  // Reallocate `new_size` bytes of memory, replacing the old region of size
  // `old_size` at `p`. In contrast to a normal realloc, this grows downwards,
  // and is intended specifcally for `vector_downward` use.
  // `in_use_back` and `in_use_front` indicate how much of `old_size` is
  // actually in use at each end, and needs to be copied.
  virtual uint8_t* reallocate_downward(uint8_t* old_p, size_t old_size, size_t new_size,
                                       size_t in_use_back, size_t in_use_front)
  {
    FLATBUFFERS_ASSERT(new_size > old_size);   // vector_downward only grows
    uint8_t* new_p = allocate(new_size);
    memcpy_downward(old_p, old_size, new_p, new_size, in_use_back, in_use_front);
    deallocate(old_p, old_size);
    return new_p;
  }

protected:
  // Called by `reallocate_downward` to copy memory from `old_p` of `old_size`
  // to `new_p` of `new_size`. Only memory of size `in_use_front` and
  // `in_use_back` will be copied from the front and back of the old memory
  // allocation.
  void memcpy_downward(uint8_t* old_p, size_t old_size, uint8_t* new_p, size_t new_size,
                       size_t in_use_back, size_t in_use_front)
  {
    memcpy(new_p + new_size - in_use_back, old_p + old_size - in_use_back, in_use_back);
    memcpy(new_p, old_p, in_use_front);
  }
};

// DefaultAllocator uses new/delete to allocate memory regions
class DefaultAllocator : public Allocator
{
public:
  uint8_t* allocate(size_t size) FLATBUFFERS_OVERRIDE
  {
    return new uint8_t[size];
  }

  void deallocate(uint8_t* p, size_t) FLATBUFFERS_OVERRIDE
  {
    delete[] p;
  }

  static void dealloc(void* p, size_t)
  {
    delete[] static_cast<uint8_t*>(p);
  }
};

// These functions allow for a null allocator to mean use the default allocator,
// as used by DetachedBuffer and vector_downward below.
// This is to avoid having a statically or dynamically allocated default
// allocator, or having to move it between the classes that may own it.
inline uint8_t* Allocate(Allocator* allocator, size_t size)
{
  return allocator ? allocator->allocate(size) : DefaultAllocator().allocate(size);
}

inline void Deallocate(Allocator* allocator, uint8_t* p, size_t size)
{
  if (allocator)
    allocator->deallocate(p, size);
  else
    DefaultAllocator().deallocate(p, size);
}

inline uint8_t* ReallocateDownward(Allocator* allocator, uint8_t* old_p, size_t old_size,
                                   size_t new_size, size_t in_use_back,
                                   size_t in_use_front)
{
  return allocator ? allocator->reallocate_downward(old_p, old_size, new_size,
                                                    in_use_back, in_use_front) :
                     DefaultAllocator().reallocate_downward(old_p, old_size, new_size,
                                                            in_use_back, in_use_front);
}

// DetachedBuffer is a finished flatbuffer memory region, detached from its
// builder. The original memory region and allocator are also stored so that
// the DetachedBuffer can manage the memory lifetime.
class DetachedBuffer
{
public:
  DetachedBuffer() :
    allocator_(nullptr),
    own_allocator_(false),
    buf_(nullptr),
    reserved_(0),
    cur_(nullptr),
    size_(0)
  {}

  DetachedBuffer(Allocator* allocator, bool own_allocator, uint8_t* buf, size_t reserved,
                 uint8_t* cur, size_t sz) :
    allocator_(allocator),
    own_allocator_(own_allocator),
    buf_(buf),
    reserved_(reserved),
    cur_(cur),
    size_(sz)
  {}

  // clang-format off
  #if !defined(FLATBUFFERS_CPP98_STL)
  // clang-format on
  DetachedBuffer(DetachedBuffer&& other) :
    allocator_(other.allocator_),
    own_allocator_(other.own_allocator_),
    buf_(other.buf_),
    reserved_(other.reserved_),
    cur_(other.cur_),
    size_(other.size_)
  {
    other.reset();
  }
  // clang-format off
  #endif  // !defined(FLATBUFFERS_CPP98_STL)
  // clang-format on

  // clang-format off
  #if !defined(FLATBUFFERS_CPP98_STL)
  // clang-format on
  DetachedBuffer& operator=(DetachedBuffer&& other)
  {
    if (this == &other)
      return *this;

    destroy();

    allocator_ = other.allocator_;
    own_allocator_ = other.own_allocator_;
    buf_ = other.buf_;
    reserved_ = other.reserved_;
    cur_ = other.cur_;
    size_ = other.size_;

    other.reset();

    return *this;
  }
  // clang-format off
  #endif  // !defined(FLATBUFFERS_CPP98_STL)
  // clang-format on

  ~DetachedBuffer()
  {
    destroy();
  }

  const uint8_t* data() const
  {
    return cur_;
  }

  uint8_t* data()
  {
    return cur_;
  }

  size_t size() const
  {
    return size_;
  }

  // clang-format off
  #if 0  // disabled for now due to the ordering of classes in this header
  template <class T>
  bool Verify() const {
    Verifier verifier(data(), size());
    return verifier.Verify<T>(nullptr);
  }

  template <class T>
  const T* GetRoot() const {
    return flatbuffers::GetRoot<T>(data());
  }

  template <class T>
  T* GetRoot() {
    return flatbuffers::GetRoot<T>(data());
  }
  #endif
  // clang-format on

  // clang-format off
  #if !defined(FLATBUFFERS_CPP98_STL)
  // clang-format on
  // These may change access mode, leave these at end of public section
  FLATBUFFERS_DELETE_FUNC(DetachedBuffer(const DetachedBuffer& other));
  FLATBUFFERS_DELETE_FUNC(DetachedBuffer& operator=(const DetachedBuffer& other));
  // clang-format off
  #endif  // !defined(FLATBUFFERS_CPP98_STL)
  // clang-format on

protected:
  Allocator* allocator_;
  bool own_allocator_;
  uint8_t* buf_;
  size_t reserved_;
  uint8_t* cur_;
  size_t size_;

  inline void destroy()
  {
    if (buf_)
      Deallocate(allocator_, buf_, reserved_);
    if (own_allocator_ && allocator_)
    {
      delete allocator_;
    }
    reset();
  }

  inline void reset()
  {
    allocator_ = nullptr;
    own_allocator_ = false;
    buf_ = nullptr;
    reserved_ = 0;
    cur_ = nullptr;
    size_ = 0;
  }
};

// This is a minimal replication of std::vector<uint8_t> functionality,
// except growing from higher to lower addresses. i.e push_back() inserts data
// in the lowest address in the vector.
// Since this vector leaves the lower part unused, we support a "scratch-pad"
// that can be stored there for temporary data, to share the allocated space.
// Essentially, this supports 2 std::vectors in a single buffer.
class vector_downward
{
public:
  explicit vector_downward(size_t initial_size, Allocator* allocator, bool own_allocator,
                           size_t buffer_minalign) :
    allocator_(allocator),
    own_allocator_(own_allocator),
    initial_size_(initial_size),
    buffer_minalign_(buffer_minalign),
    reserved_(0),
    buf_(nullptr),
    cur_(nullptr),
    scratch_(nullptr)
  {}

  // clang-format off
  #if !defined(FLATBUFFERS_CPP98_STL)
  vector_downward(vector_downward &&other)
  #else
  vector_downward(vector_downward &other)
  #endif  // defined(FLATBUFFERS_CPP98_STL)
    // clang-format on
    :
    allocator_(other.allocator_),
    own_allocator_(other.own_allocator_),
    initial_size_(other.initial_size_),
    buffer_minalign_(other.buffer_minalign_),
    reserved_(other.reserved_),
    buf_(other.buf_),
    cur_(other.cur_),
    scratch_(other.scratch_)
  {
    // No change in other.allocator_
    // No change in other.initial_size_
    // No change in other.buffer_minalign_
    other.own_allocator_ = false;
    other.reserved_ = 0;
    other.buf_ = nullptr;
    other.cur_ = nullptr;
    other.scratch_ = nullptr;
  }

  // clang-format off
  #if !defined(FLATBUFFERS_CPP98_STL)
  // clang-format on
  vector_downward& operator=(vector_downward&& other)
  {
    // Move construct a temporary and swap idiom
    vector_downward temp(std::move(other));
    swap(temp);
    return *this;
  }
  // clang-format off
  #endif  // defined(FLATBUFFERS_CPP98_STL)
  // clang-format on

  ~vector_downward()
  {
    clear_buffer();
    clear_allocator();
  }

  void reset()
  {
    clear_buffer();
    clear();
  }

  void clear()
  {
    if (buf_)
    {
      cur_ = buf_ + reserved_;
    }
    else
    {
      reserved_ = 0;
      cur_ = nullptr;
    }
    clear_scratch();
  }

  void clear_scratch()
  {
    scratch_ = buf_;
  }

  void clear_allocator()
  {
    if (own_allocator_ && allocator_)
    {
      delete allocator_;
    }
    allocator_ = nullptr;
    own_allocator_ = false;
  }

  void clear_buffer()
  {
    if (buf_)
      Deallocate(allocator_, buf_, reserved_);
    buf_ = nullptr;
  }

  // Relinquish the pointer to the caller.
  uint8_t* release_raw(size_t& allocated_bytes, size_t& offset)
  {
    auto* buf = buf_;
    allocated_bytes = reserved_;
    offset = static_cast<size_t>(cur_ - buf_);

    // release_raw only relinquishes the buffer ownership.
    // Does not deallocate or reset the allocator. Destructor will do that.
    buf_ = nullptr;
    clear();
    return buf;
  }

  // Relinquish the pointer to the caller.
  DetachedBuffer release()
  {
    // allocator ownership (if any) is transferred to DetachedBuffer.
    DetachedBuffer fb(allocator_, own_allocator_, buf_, reserved_, cur_, size());
    if (own_allocator_)
    {
      allocator_ = nullptr;
      own_allocator_ = false;
    }
    buf_ = nullptr;
    clear();
    return fb;
  }

  size_t ensure_space(size_t len)
  {
    FLATBUFFERS_ASSERT(cur_ >= scratch_ && scratch_ >= buf_);
    if (len > static_cast<size_t>(cur_ - scratch_))
    {
      reallocate(len);
    }
    // Beyond this, signed offsets may not have enough range:
    // (FlatBuffers > 2GB not supported).
    FLATBUFFERS_ASSERT(size() < FLATBUFFERS_MAX_BUFFER_SIZE);
    return len;
  }

  inline uint8_t* make_space(size_t len)
  {
    size_t space = ensure_space(len);
    cur_ -= space;
    return cur_;
  }

  // Returns nullptr if using the DefaultAllocator.
  Allocator* get_custom_allocator()
  {
    return allocator_;
  }

  uoffset_t size() const
  {
    return static_cast<uoffset_t>(reserved_ - static_cast<size_t>(cur_ - buf_));
  }

  uoffset_t scratch_size() const
  {
    return static_cast<uoffset_t>(scratch_ - buf_);
  }

  size_t capacity() const
  {
    return reserved_;
  }

  uint8_t* data() const
  {
    FLATBUFFERS_ASSERT(cur_);
    return cur_;
  }

  uint8_t* scratch_data() const
  {
    FLATBUFFERS_ASSERT(buf_);
    return buf_;
  }

  uint8_t* scratch_end() const
  {
    FLATBUFFERS_ASSERT(scratch_);
    return scratch_;
  }

  uint8_t* data_at(size_t offset) const
  {
    return buf_ + reserved_ - offset;
  }

  void push(const uint8_t* bytes, size_t num)
  {
    if (num > 0)
    {
      memcpy(make_space(num), bytes, num);
    }
  }

  // Specialized version of push() that avoids memcpy call for small data.
  template <typename T>
  void push_small(const T& little_endian_t)
  {
    make_space(sizeof(T));
    *reinterpret_cast<T*>(cur_) = little_endian_t;
  }

  template <typename T>
  void scratch_push_small(const T& t)
  {
    ensure_space(sizeof(T));
    *reinterpret_cast<T*>(scratch_) = t;
    scratch_ += sizeof(T);
  }

  // fill() is most frequently called with small byte counts (<= 4),
  // which is why we're using loops rather than calling memset.
  void fill(size_t zero_pad_bytes)
  {
    make_space(zero_pad_bytes);
    for (size_t i = 0; i < zero_pad_bytes; i++)
      cur_[i] = 0;
  }

  // Version for when we know the size is larger.
  // Precondition: zero_pad_bytes > 0
  void fill_big(size_t zero_pad_bytes)
  {
    memset(make_space(zero_pad_bytes), 0, zero_pad_bytes);
  }

  void pop(size_t bytes_to_remove)
  {
    cur_ += bytes_to_remove;
  }
  void scratch_pop(size_t bytes_to_remove)
  {
    scratch_ -= bytes_to_remove;
  }

  void swap(vector_downward& other)
  {
    using std::swap;
    swap(allocator_, other.allocator_);
    swap(own_allocator_, other.own_allocator_);
    swap(initial_size_, other.initial_size_);
    swap(buffer_minalign_, other.buffer_minalign_);
    swap(reserved_, other.reserved_);
    swap(buf_, other.buf_);
    swap(cur_, other.cur_);
    swap(scratch_, other.scratch_);
  }

  void swap_allocator(vector_downward& other)
  {
    using std::swap;
    swap(allocator_, other.allocator_);
    swap(own_allocator_, other.own_allocator_);
  }

private:
  // You shouldn't really be copying instances of this class.
  FLATBUFFERS_DELETE_FUNC(vector_downward(const vector_downward&));
  FLATBUFFERS_DELETE_FUNC(vector_downward& operator=(const vector_downward&));

  Allocator* allocator_;
  bool own_allocator_;
  size_t initial_size_;
  size_t buffer_minalign_;
  size_t reserved_;
  uint8_t* buf_;
  uint8_t* cur_;       // Points at location between empty (below) and used (above).
  uint8_t* scratch_;   // Points to the end of the scratchpad in use.

  void reallocate(size_t len)
  {
    auto old_reserved = reserved_;
    auto old_size = size();
    auto old_scratch_size = scratch_size();
    reserved_ += (std::max)(len, old_reserved ? old_reserved / 2 : initial_size_);
    reserved_ = (reserved_ + buffer_minalign_ - 1) & ~(buffer_minalign_ - 1);
    if (buf_)
    {
      buf_ = ReallocateDownward(allocator_, buf_, old_reserved, reserved_, old_size,
                                old_scratch_size);
    }
    else
    {
      buf_ = Allocate(allocator_, reserved_);
    }
    cur_ = buf_ + reserved_ - old_size;
    scratch_ = buf_ + old_scratch_size;
  }
};

// Converts a Field ID to a virtual table offset.
inline voffset_t FieldIndexToOffset(voffset_t field_id)
{
  // Should correspond to what EndTable() below builds up.
  const int fixed_fields = 2;   // Vtable size and Object Size.
  return static_cast<voffset_t>((field_id + fixed_fields) * sizeof(voffset_t));
}

template <typename T, typename Alloc>
const T* data(const std::vector<T, Alloc>& v)
{
  // Eventually the returned pointer gets passed down to memcpy, so
  // we need it to be non-null to avoid undefined behavior.
  static uint8_t t;
  return v.empty() ? reinterpret_cast<const T*>(&t) : &v.front();
}
template <typename T, typename Alloc>
T* data(std::vector<T, Alloc>& v)
{
  // Eventually the returned pointer gets passed down to memcpy, so
  // we need it to be non-null to avoid undefined behavior.
  static uint8_t t;
  return v.empty() ? reinterpret_cast<T*>(&t) : &v.front();
}


class FlatBufferBuilder
{
public:
  explicit FlatBufferBuilder(size_t initial_size = 1024, Allocator* allocator = nullptr,
                             bool own_allocator = false,
                             size_t buffer_minalign = AlignOf<largest_scalar_t>()) :
    buf_(initial_size, allocator, own_allocator, buffer_minalign),
    num_field_loc(0),
    max_voffset_(0),
    nested(false),
    finished(false),
    minalign_(1),
    force_defaults_(false),
    dedup_vtables_(true),
    string_pool(nullptr)
  {
    EndianCheck();
  }

  // clang-format off
  #if !defined(FLATBUFFERS_CPP98_STL)
  FlatBufferBuilder(FlatBufferBuilder &&other)
  #else
  FlatBufferBuilder(FlatBufferBuilder &other)
  #endif  // #if !defined(FLATBUFFERS_CPP98_STL)
    : buf_(1024, nullptr, false, AlignOf<largest_scalar_t>()),
      num_field_loc(0),
      max_voffset_(0),
      nested(false),
      finished(false),
      minalign_(1),
      force_defaults_(false),
      dedup_vtables_(true),
      string_pool(nullptr) {
    EndianCheck();
    // Default construct and swap idiom.
    // Lack of delegating constructors in vs2010 makes it more verbose than needed.
    Swap(other);
  }
  // clang-format on

  // clang-format off
  #if !defined(FLATBUFFERS_CPP98_STL)
  // clang-format on
  FlatBufferBuilder& operator=(FlatBufferBuilder&& other)
  {
    // Move construct a temporary and swap idiom
    FlatBufferBuilder temp(std::move(other));
    Swap(temp);
    return *this;
  }
  // clang-format off
  #endif  // defined(FLATBUFFERS_CPP98_STL)
  // clang-format on

  void Swap(FlatBufferBuilder& other)
  {
    using std::swap;
    buf_.swap(other.buf_);
    swap(num_field_loc, other.num_field_loc);
    swap(max_voffset_, other.max_voffset_);
    swap(nested, other.nested);
    swap(finished, other.finished);
    swap(minalign_, other.minalign_);
    swap(force_defaults_, other.force_defaults_);
    swap(dedup_vtables_, other.dedup_vtables_);
    swap(string_pool, other.string_pool);
  }

  ~FlatBufferBuilder()
  {
    if (string_pool)
      delete string_pool;
  }

  void Reset()
  {
    Clear();        // clear builder state
    buf_.reset();   // deallocate buffer
  }

  void Clear()
  {
    ClearOffsets();
    buf_.clear();
    nested = false;
    finished = false;
    minalign_ = 1;
    if (string_pool)
      string_pool->clear();
  }

  uoffset_t GetSize() const
  {
    return buf_.size();
  }

  uint8_t* GetBufferPointer() const
  {
    Finished();
    return buf_.data();
  }

  flatbuffers::span<uint8_t> GetBufferSpan() const
  {
    Finished();
    return flatbuffers::span<uint8_t>(buf_.data(), buf_.size());
  }

  uint8_t* GetCurrentBufferPointer() const
  {
    return buf_.data();
  }

  FLATBUFFERS_ATTRIBUTE(deprecated("use Release() instead"))
  DetachedBuffer ReleaseBufferPointer()
  {
    Finished();
    return buf_.release();
  }

  DetachedBuffer Release()
  {
    Finished();
    return buf_.release();
  }

  uint8_t* ReleaseRaw(size_t& size, size_t& offset)
  {
    Finished();
    return buf_.release_raw(size, offset);
  }

  size_t GetBufferMinAlignment() const
  {
    Finished();
    return minalign_;
  }

  void Finished() const
  {
    // If you get this assert, you're attempting to get access a buffer
    // which hasn't been finished yet. Be sure to call
    // FlatBufferBuilder::Finish with your root table.
    // If you really need to access an unfinished buffer, call
    // GetCurrentBufferPointer instead.
    FLATBUFFERS_ASSERT(finished);
  }

  void ForceDefaults(bool fd)
  {
    force_defaults_ = fd;
  }

  void DedupVtables(bool dedup)
  {
    dedup_vtables_ = dedup;
  }

  void Pad(size_t num_bytes)
  {
    buf_.fill(num_bytes);
  }

  void TrackMinAlign(size_t elem_size)
  {
    if (elem_size > minalign_)
      minalign_ = elem_size;
  }

  void Align(size_t elem_size)
  {
    TrackMinAlign(elem_size);
    buf_.fill(PaddingBytes(buf_.size(), elem_size));
  }

  void PushFlatBuffer(const uint8_t* bytes, size_t size)
  {
    PushBytes(bytes, size);
    finished = true;
  }

  void PushBytes(const uint8_t* bytes, size_t size)
  {
    buf_.push(bytes, size);
  }

  void PopBytes(size_t amount)
  {
    buf_.pop(amount);
  }

  template <typename T>
  void AssertScalarT()
  {
    // The code assumes power of 2 sizes and endian-swap-ability.
    static_assert(flatbuffers::is_scalar<T>::value, "T must be a scalar type");
  }

  // Write a single aligned scalar to the buffer
  template <typename T>
  uoffset_t PushElement(T element)
  {
    AssertScalarT<T>();
    T litle_endian_element = EndianScalar(element);
    Align(sizeof(T));
    buf_.push_small(litle_endian_element);
    return GetSize();
  }

  template <typename T>
  uoffset_t PushElement(Offset<T> off)
  {
    // Special case for offsets: see ReferTo below.
    return PushElement(ReferTo(off.o));
  }

  // When writing fields, we track where they are, so we can create correct
  // vtables later.
  void TrackField(voffset_t field, uoffset_t off)
  {
    FieldLoc fl = {off, field};
    buf_.scratch_push_small(fl);
    num_field_loc++;
    max_voffset_ = (std::max)(max_voffset_, field);
  }

  // Like PushElement, but additionally tracks the field this represents.
  template <typename T>
  void AddElement(voffset_t field, T e, T def)
  {
    // We don't serialize values equal to the default.
    if (IsTheSameAs(e, def) && !force_defaults_)
      return;
    auto off = PushElement(e);
    TrackField(field, off);
  }

  template <typename T>
  void AddElement(voffset_t field, T e)
  {
    auto off = PushElement(e);
    TrackField(field, off);
  }

  template <typename T>
  void AddOffset(voffset_t field, Offset<T> off)
  {
    if (off.IsNull())
      return;   // Don't store.
    AddElement(field, ReferTo(off.o), static_cast<uoffset_t>(0));
  }

  template <typename T>
  void AddStruct(voffset_t field, const T* structptr)
  {
    if (!structptr)
      return;   // Default, don't store.
    Align(AlignOf<T>());
    buf_.push_small(*structptr);
    TrackField(field, GetSize());
  }

  void AddStructOffset(voffset_t field, uoffset_t off)
  {
    TrackField(field, off);
  }

  // Offsets initially are relative to the end of the buffer (downwards).
  // This function converts them to be relative to the current location
  // in the buffer (when stored here), pointing upwards.
  uoffset_t ReferTo(uoffset_t off)
  {
    // Align to ensure GetSize() below is correct.
    Align(sizeof(uoffset_t));
    // Offset must refer to something already in buffer.
    FLATBUFFERS_ASSERT(off && off <= GetSize());
    return GetSize() - off + static_cast<uoffset_t>(sizeof(uoffset_t));
  }

  void NotNested()
  {
    // If you hit this, you're trying to construct a Table/Vector/String
    // during the construction of its parent table (between the MyTableBuilder
    // and table.Finish().
    // Move the creation of these sub-objects to above the MyTableBuilder to
    // not get this assert.
    // Ignoring this assert may appear to work in simple cases, but the reason
    // it is here is that storing objects in-line may cause vtable offsets
    // to not fit anymore. It also leads to vtable duplication.
    FLATBUFFERS_ASSERT(!nested);
    // If you hit this, fields were added outside the scope of a table.
    FLATBUFFERS_ASSERT(!num_field_loc);
  }

  // From generated code (or from the parser), we call StartTable/EndTable
  // with a sequence of AddElement calls in between.
  uoffset_t StartTable()
  {
    NotNested();
    nested = true;
    return GetSize();
  }

  // This finishes one serialized object by generating the vtable if it's a
  // table, comparing it against existing vtables, and writing the
  // resulting vtable offset.
  uoffset_t EndTable(uoffset_t start)
  {
    // If you get this assert, a corresponding StartTable wasn't called.
    FLATBUFFERS_ASSERT(nested);
    // Write the vtable offset, which is the start of any Table.
    // We fill it's value later.
    auto vtableoffsetloc = PushElement<soffset_t>(0);
    // Write a vtable, which consists entirely of voffset_t elements.
    // It starts with the number of offsets, followed by a type id, followed
    // by the offsets themselves. In reverse:
    // Include space for the last offset and ensure empty tables have a
    // minimum size.
    max_voffset_ = (std::max)(static_cast<voffset_t>(max_voffset_ + sizeof(voffset_t)),
                              FieldIndexToOffset(0));
    buf_.fill_big(max_voffset_);
    auto table_object_size = vtableoffsetloc - start;
    // Vtable use 16bit offsets.
    FLATBUFFERS_ASSERT(table_object_size < 0x10000);
    WriteScalar<voffset_t>(buf_.data() + sizeof(voffset_t),
                           static_cast<voffset_t>(table_object_size));
    WriteScalar<voffset_t>(buf_.data(), max_voffset_);
    // Write the offsets into the table
    for (auto it = buf_.scratch_end() - num_field_loc * sizeof(FieldLoc);
         it < buf_.scratch_end(); it += sizeof(FieldLoc))
    {
      auto field_location = reinterpret_cast<FieldLoc*>(it);
      auto pos = static_cast<voffset_t>(vtableoffsetloc - field_location->off);
      // If this asserts, it means you've set a field twice.
      FLATBUFFERS_ASSERT(!ReadScalar<voffset_t>(buf_.data() + field_location->id));
      WriteScalar<voffset_t>(buf_.data() + field_location->id, pos);
    }
    ClearOffsets();
    auto vt1 = reinterpret_cast<voffset_t*>(buf_.data());
    auto vt1_size = ReadScalar<voffset_t>(vt1);
    auto vt_use = GetSize();
    // See if we already have generated a vtable with this exact same
    // layout before. If so, make it point to the old one, remove this one.
    if (dedup_vtables_)
    {
      for (auto it = buf_.scratch_data(); it < buf_.scratch_end();
           it += sizeof(uoffset_t))
      {
        auto vt_offset_ptr = reinterpret_cast<uoffset_t*>(it);
        auto vt2 = reinterpret_cast<voffset_t*>(buf_.data_at(*vt_offset_ptr));
        auto vt2_size = ReadScalar<voffset_t>(vt2);
        if (vt1_size != vt2_size || 0 != memcmp(vt2, vt1, vt1_size))
          continue;
        vt_use = *vt_offset_ptr;
        buf_.pop(GetSize() - vtableoffsetloc);
        break;
      }
    }
    // If this is a new vtable, remember it.
    if (vt_use == GetSize())
    {
      buf_.scratch_push_small(vt_use);
    }
    // Fill the vtable offset we created above.
    // The offset points from the beginning of the object to where the
    // vtable is stored.
    // Offsets default direction is downward in memory for future format
    // flexibility (storing all vtables at the start of the file).
    WriteScalar(buf_.data_at(vtableoffsetloc),
                static_cast<soffset_t>(vt_use) - static_cast<soffset_t>(vtableoffsetloc));

    nested = false;
    return vtableoffsetloc;
  }

  FLATBUFFERS_ATTRIBUTE(deprecated("call the version above instead"))
  uoffset_t EndTable(uoffset_t start, voffset_t /*numfields*/)
  {
    return EndTable(start);
  }

  // This checks a required field has been set in a given table that has
  // just been constructed.
  template <typename T>
  void Required(Offset<T> table, voffset_t field);

  uoffset_t StartStruct(size_t alignment)
  {
    Align(alignment);
    return GetSize();
  }

  uoffset_t EndStruct()
  {
    return GetSize();
  }

  void ClearOffsets()
  {
    buf_.scratch_pop(num_field_loc * sizeof(FieldLoc));
    num_field_loc = 0;
    max_voffset_ = 0;
  }

  // Aligns such that when "len" bytes are written, an object can be written
  // after it with "alignment" without padding.
  void PreAlign(size_t len, size_t alignment)
  {
    TrackMinAlign(alignment);
    buf_.fill(PaddingBytes(GetSize() + len, alignment));
  }
  template <typename T>
  void PreAlign(size_t len)
  {
    AssertScalarT<T>();
    PreAlign(len, sizeof(T));
  }

  Offset<String> CreateString(const char* str, size_t len)
  {
    NotNested();
    PreAlign<uoffset_t>(len + 1);   // Always 0-terminated.
    buf_.fill(1);
    PushBytes(reinterpret_cast<const uint8_t*>(str), len);
    PushElement(static_cast<uoffset_t>(len));
    return Offset<String>(GetSize());
  }

  Offset<String> CreateString(const char* str)
  {
    return CreateString(str, strlen(str));
  }

  Offset<String> CreateString(char* str)
  {
    return CreateString(str, strlen(str));
  }

  Offset<String> CreateString(const std::string& str)
  {
    return CreateString(str.c_str(), str.length());
  }

  // clang-format off
  #ifdef FLATBUFFERS_HAS_STRING_VIEW
  Offset<String> CreateString(flatbuffers::string_view str) {
    return CreateString(str.data(), str.size());
  }
  #endif // FLATBUFFERS_HAS_STRING_VIEW
  // clang-format on

  Offset<String> CreateString(const String* str)
  {
    return str ? CreateString(str->c_str(), str->size()) : 0;
  }

  template <typename T>
  Offset<String> CreateString(const T& str)
  {
    return CreateString(str.c_str(), str.length());
  }

  Offset<String> CreateSharedString(const char* str, size_t len)
  {
    if (!string_pool)
      string_pool = new StringOffsetMap(StringOffsetCompare(buf_));
    auto size_before_string = buf_.size();
    // Must first serialize the string, since the set is all offsets into
    // buffer.
    auto off = CreateString(str, len);
    auto it = string_pool->find(off);
    // If it exists we reuse existing serialized data!
    if (it != string_pool->end())
    {
      // We can remove the string we serialized.
      buf_.pop(buf_.size() - size_before_string);
      return *it;
    }
    // Record this string for future use.
    string_pool->insert(off);
    return off;
  }

#ifdef FLATBUFFERS_HAS_STRING_VIEW
  Offset<String> CreateSharedString(const flatbuffers::string_view str)
  {
    return CreateSharedString(str.data(), str.size());
  }
#else
  Offset<String> CreateSharedString(const char* str)
  {
    return CreateSharedString(str, strlen(str));
  }

  Offset<String> CreateSharedString(const std::string& str)
  {
    return CreateSharedString(str.c_str(), str.length());
  }
#endif

  Offset<String> CreateSharedString(const String* str)
  {
    return CreateSharedString(str->c_str(), str->size());
  }

  uoffset_t EndVector(size_t len)
  {
    FLATBUFFERS_ASSERT(nested);   // Hit if no corresponding StartVector.
    nested = false;
    return PushElement(static_cast<uoffset_t>(len));
  }

  void StartVector(size_t len, size_t elemsize)
  {
    NotNested();
    nested = true;
    PreAlign<uoffset_t>(len * elemsize);
    PreAlign(len * elemsize, elemsize);   // Just in case elemsize > uoffset_t.
  }

  // Call this right before StartVector/CreateVector if you want to force the
  // alignment to be something different than what the element size would
  // normally dictate.
  // This is useful when storing a nested_flatbuffer in a vector of bytes,
  // or when storing SIMD floats, etc.
  void ForceVectorAlignment(size_t len, size_t elemsize, size_t alignment)
  {
    FLATBUFFERS_ASSERT(VerifyAlignmentRequirements(alignment));
    PreAlign(len * elemsize, alignment);
  }

  // Similar to ForceVectorAlignment but for String fields.
  void ForceStringAlignment(size_t len, size_t alignment)
  {
    FLATBUFFERS_ASSERT(VerifyAlignmentRequirements(alignment));
    PreAlign((len + 1) * sizeof(char), alignment);
  }


  template <typename T>
  Offset<Vector<T>> CreateVector(const T* v, size_t len)
  {
    // If this assert hits, you're specifying a template argument that is
    // causing the wrong overload to be selected, remove it.
    AssertScalarT<T>();
    StartVector(len, sizeof(T));
    if (len == 0)
    {
      return Offset<Vector<T>>(EndVector(len));
    }
    // clang-format off
    #if FLATBUFFERS_LITTLEENDIAN
      PushBytes(reinterpret_cast<const uint8_t *>(v), len * sizeof(T));
    #else
      if (sizeof(T) == 1) {
        PushBytes(reinterpret_cast<const uint8_t *>(v), len);
      } else {
        for (auto i = len; i > 0; ) {
          PushElement(v[--i]);
        }
      }
    #endif
    // clang-format on
    return Offset<Vector<T>>(EndVector(len));
  }

  template <typename T>
  Offset<Vector<Offset<T>>> CreateVector(const Offset<T>* v, size_t len)
  {
    StartVector(len, sizeof(Offset<T>));
    for (auto i = len; i > 0;)
    {
      PushElement(v[--i]);
    }
    return Offset<Vector<Offset<T>>>(EndVector(len));
  }

  template <typename T>
  Offset<Vector<T>> CreateVector(const std::vector<T>& v)
  {
    return CreateVector(data(v), v.size());
  }

  // vector<bool> may be implemented using a bit-set, so we can't access it as
  // an array. Instead, read elements manually.
  // Background: https://isocpp.org/blog/2012/11/on-vectorbool
  Offset<Vector<uint8_t>> CreateVector(const std::vector<bool>& v)
  {
    StartVector(v.size(), sizeof(uint8_t));
    for (auto i = v.size(); i > 0;)
    {
      PushElement(static_cast<uint8_t>(v[--i]));
    }
    return Offset<Vector<uint8_t>>(EndVector(v.size()));
  }

  // clang-format off
  #ifndef FLATBUFFERS_CPP98_STL
  template<typename T> Offset<Vector<T>> CreateVector(size_t vector_size,
      const std::function<T (size_t i)> &f) {
    std::vector<T> elems(vector_size);
    for (size_t i = 0; i < vector_size; i++) elems[i] = f(i);
    return CreateVector(elems);
  }
  #endif
  // clang-format on

  template <typename T, typename F, typename S>
  Offset<Vector<T>> CreateVector(size_t vector_size, F f, S* state)
  {
    std::vector<T> elems(vector_size);
    for (size_t i = 0; i < vector_size; i++)
      elems[i] = f(i, state);
    return CreateVector(elems);
  }

  Offset<Vector<Offset<String>>> CreateVectorOfStrings(const std::vector<std::string>& v)
  {
    std::vector<Offset<String>> offsets(v.size());
    for (size_t i = 0; i < v.size(); i++)
      offsets[i] = CreateString(v[i]);
    return CreateVector(offsets);
  }

  template <typename T>
  Offset<Vector<const T*>> CreateVectorOfStructs(const T* v, size_t len)
  {
    StartVector(len * sizeof(T) / AlignOf<T>(), AlignOf<T>());
    PushBytes(reinterpret_cast<const uint8_t*>(v), sizeof(T) * len);
    return Offset<Vector<const T*>>(EndVector(len));
  }

  template <typename T, typename S>
  Offset<Vector<const T*>> CreateVectorOfNativeStructs(const S* v, size_t len,
                                                       T((*const pack_func)(const S&)))
  {
    FLATBUFFERS_ASSERT(pack_func);
    std::vector<T> vv(len);
    std::transform(v, v + len, vv.begin(), pack_func);
    return CreateVectorOfStructs<T>(data(vv), vv.size());
  }

  template <typename T, typename S>
  Offset<Vector<const T*>> CreateVectorOfNativeStructs(const S* v, size_t len)
  {
    extern T Pack(const S&);
    return CreateVectorOfNativeStructs(v, len, Pack);
  }

  // clang-format off
  #ifndef FLATBUFFERS_CPP98_STL
  template<typename T> Offset<Vector<const T *>> CreateVectorOfStructs(
      size_t vector_size, const std::function<void(size_t i, T *)> &filler) {
    T* structs = StartVectorOfStructs<T>(vector_size);
    for (size_t i = 0; i < vector_size; i++) {
      filler(i, structs);
      structs++;
    }
    return EndVectorOfStructs<T>(vector_size);
  }
  #endif
  // clang-format on

  template <typename T, typename F, typename S>
  Offset<Vector<const T*>> CreateVectorOfStructs(size_t vector_size, F f, S* state)
  {
    T* structs = StartVectorOfStructs<T>(vector_size);
    for (size_t i = 0; i < vector_size; i++)
    {
      f(i, structs, state);
      structs++;
    }
    return EndVectorOfStructs<T>(vector_size);
  }

  template <typename T, typename Alloc>
  Offset<Vector<const T*>> CreateVectorOfStructs(const std::vector<T, Alloc>& v)
  {
    return CreateVectorOfStructs(data(v), v.size());
  }

  template <typename T, typename S>
  Offset<Vector<const T*>> CreateVectorOfNativeStructs(const std::vector<S>& v,
                                                       T((*const pack_func)(const S&)))
  {
    return CreateVectorOfNativeStructs<T, S>(data(v), v.size(), pack_func);
  }

  template <typename T, typename S>
  Offset<Vector<const T*>> CreateVectorOfNativeStructs(const std::vector<S>& v)
  {
    return CreateVectorOfNativeStructs<T, S>(data(v), v.size());
  }

  template <typename T>
  struct StructKeyComparator
  {
    bool operator()(const T& a, const T& b) const
    {
      return a.KeyCompareLessThan(&b);
    }

    FLATBUFFERS_DELETE_FUNC(StructKeyComparator& operator=(const StructKeyComparator&));
  };

  template <typename T>
  Offset<Vector<const T*>> CreateVectorOfSortedStructs(std::vector<T>* v)
  {
    return CreateVectorOfSortedStructs(data(*v), v->size());
  }

  template <typename T, typename S>
  Offset<Vector<const T*>> CreateVectorOfSortedNativeStructs(std::vector<S>* v)
  {
    return CreateVectorOfSortedNativeStructs<T, S>(data(*v), v->size());
  }

  template <typename T>
  Offset<Vector<const T*>> CreateVectorOfSortedStructs(T* v, size_t len)
  {
    std::sort(v, v + len, StructKeyComparator<T>());
    return CreateVectorOfStructs(v, len);
  }

  template <typename T, typename S>
  Offset<Vector<const T*>> CreateVectorOfSortedNativeStructs(S* v, size_t len)
  {
    extern T Pack(const S&);
    typedef T (*Pack_t)(const S&);
    std::vector<T> vv(len);
    std::transform(v, v + len, vv.begin(), static_cast<Pack_t&>(Pack));
    return CreateVectorOfSortedStructs<T>(vv, len);
  }

  template <typename T>
  struct TableKeyComparator
  {
    TableKeyComparator(vector_downward& buf) : buf_(buf)
    {}
    TableKeyComparator(const TableKeyComparator& other) : buf_(other.buf_)
    {}
    bool operator()(const Offset<T>& a, const Offset<T>& b) const
    {
      auto table_a = reinterpret_cast<T*>(buf_.data_at(a.o));
      auto table_b = reinterpret_cast<T*>(buf_.data_at(b.o));
      return table_a->KeyCompareLessThan(table_b);
    }
    vector_downward& buf_;

  private:
    FLATBUFFERS_DELETE_FUNC(
        TableKeyComparator& operator=(const TableKeyComparator& other));
  };

  template <typename T>
  Offset<Vector<Offset<T>>> CreateVectorOfSortedTables(Offset<T>* v, size_t len)
  {
    std::sort(v, v + len, TableKeyComparator<T>(buf_));
    return CreateVector(v, len);
  }

  template <typename T>
  Offset<Vector<Offset<T>>> CreateVectorOfSortedTables(std::vector<Offset<T>>* v)
  {
    return CreateVectorOfSortedTables(data(*v), v->size());
  }

  uoffset_t CreateUninitializedVector(size_t len, size_t elemsize, uint8_t** buf)
  {
    NotNested();
    StartVector(len, elemsize);
    buf_.make_space(len * elemsize);
    auto vec_start = GetSize();
    auto vec_end = EndVector(len);
    *buf = buf_.data_at(vec_start);
    return vec_end;
  }

  template <typename T>
  Offset<Vector<T>> CreateUninitializedVector(size_t len, T** buf)
  {
    AssertScalarT<T>();
    return CreateUninitializedVector(len, sizeof(T), reinterpret_cast<uint8_t**>(buf));
  }

  template <typename T>
  Offset<Vector<const T*>> CreateUninitializedVectorOfStructs(size_t len, T** buf)
  {
    return CreateUninitializedVector(len, sizeof(T), reinterpret_cast<uint8_t**>(buf));
  }

  // @brief Create a vector of scalar type T given as input a vector of scalar
  // type U, useful with e.g. pre "enum class" enums, or any existing scalar
  // data of the wrong type.
  template <typename T, typename U>
  Offset<Vector<T>> CreateVectorScalarCast(const U* v, size_t len)
  {
    AssertScalarT<T>();
    AssertScalarT<U>();
    StartVector(len, sizeof(T));
    for (auto i = len; i > 0;)
    {
      PushElement(static_cast<T>(v[--i]));
    }
    return Offset<Vector<T>>(EndVector(len));
  }

  template <typename T>
  Offset<const T*> CreateStruct(const T& structobj)
  {
    NotNested();
    Align(AlignOf<T>());
    buf_.push_small(structobj);
    return Offset<const T*>(GetSize());
  }

  static const size_t kFileIdentifierLength = 4;

  template <typename T>
  void Finish(Offset<T> root, const char* file_identifier = nullptr)
  {
    Finish(root.o, file_identifier, false);
  }

  template <typename T>
  void FinishSizePrefixed(Offset<T> root, const char* file_identifier = nullptr)
  {
    Finish(root.o, file_identifier, true);
  }

  void SwapBufAllocator(FlatBufferBuilder& other)
  {
    buf_.swap_allocator(other.buf_);
  }

protected:
  // You shouldn't really be copying instances of this class.
  FlatBufferBuilder(const FlatBufferBuilder&);
  FlatBufferBuilder& operator=(const FlatBufferBuilder&);

  void Finish(uoffset_t root, const char* file_identifier, bool size_prefix)
  {
    NotNested();
    buf_.clear_scratch();
    // This will cause the whole buffer to be aligned.
    PreAlign((size_prefix ? sizeof(uoffset_t) : 0) + sizeof(uoffset_t) +
                 (file_identifier ? kFileIdentifierLength : 0),
             minalign_);
    if (file_identifier)
    {
      FLATBUFFERS_ASSERT(strlen(file_identifier) == kFileIdentifierLength);
      PushBytes(reinterpret_cast<const uint8_t*>(file_identifier), kFileIdentifierLength);
    }
    PushElement(ReferTo(root));   // Location of root.
    if (size_prefix)
    {
      PushElement(GetSize());
    }
    finished = true;
  }

  struct FieldLoc
  {
    uoffset_t off;
    voffset_t id;
  };

  vector_downward buf_;

  // Accumulating offsets of table members while it is being built.
  // We store these in the scratch pad of buf_, after the vtable offsets.
  uoffset_t num_field_loc;
  // Track how much of the vtable is in use, so we can output the most compact
  // possible vtable.
  voffset_t max_voffset_;

  // Ensure objects are not nested.
  bool nested;

  // Ensure the buffer is finished before it is being accessed.
  bool finished;

  size_t minalign_;

  bool force_defaults_;   // Serialize values equal to their defaults anyway.

  bool dedup_vtables_;

  struct StringOffsetCompare
  {
    StringOffsetCompare(const vector_downward& buf) : buf_(&buf)
    {}
    bool operator()(const Offset<String>& a, const Offset<String>& b) const
    {
      auto stra = reinterpret_cast<const String*>(buf_->data_at(a.o));
      auto strb = reinterpret_cast<const String*>(buf_->data_at(b.o));
      return StringLessThan(stra->data(), stra->size(), strb->data(), strb->size());
    }
    const vector_downward* buf_;
  };

  // For use with CreateSharedString. Instantiated on first use only.
  typedef std::set<Offset<String>, StringOffsetCompare> StringOffsetMap;
  StringOffsetMap* string_pool;

private:
  // Allocates space for a vector of structures.
  // Must be completed with EndVectorOfStructs().
  template <typename T>
  T* StartVectorOfStructs(size_t vector_size)
  {
    StartVector(vector_size * sizeof(T) / AlignOf<T>(), AlignOf<T>());
    return reinterpret_cast<T*>(buf_.make_space(vector_size * sizeof(T)));
  }

  // End the vector of structues in the flatbuffers.
  // Vector should have previously be started with StartVectorOfStructs().
  template <typename T>
  Offset<Vector<const T*>> EndVectorOfStructs(size_t vector_size)
  {
    return Offset<Vector<const T*>>(EndVector(vector_size));
  }
};

// Helpers to get a typed pointer to the root object contained in the buffer.
template <typename T>
T* GetMutableRoot(void* buf)
{
  EndianCheck();
  return reinterpret_cast<T*>(reinterpret_cast<uint8_t*>(buf) +
                              EndianScalar(*reinterpret_cast<uoffset_t*>(buf)));
}

template <typename T>
const T* GetRoot(const void* buf)
{
  return GetMutableRoot<T>(const_cast<void*>(buf));
}

template <typename T>
const T* GetSizePrefixedRoot(const void* buf)
{
  return GetRoot<T>(reinterpret_cast<const uint8_t*>(buf) + sizeof(uoffset_t));
}

template <typename T>
T* GetMutableTemporaryPointer(FlatBufferBuilder& fbb, Offset<T> offset)
{
  return reinterpret_cast<T*>(fbb.GetCurrentBufferPointer() + fbb.GetSize() - offset.o);
}

template <typename T>
const T* GetTemporaryPointer(FlatBufferBuilder& fbb, Offset<T> offset)
{
  return GetMutableTemporaryPointer<T>(fbb, offset);
}

inline const char* GetBufferIdentifier(const void* buf, bool size_prefixed = false)
{
  return reinterpret_cast<const char*>(buf) +
         ((size_prefixed) ? 2 * sizeof(uoffset_t) : sizeof(uoffset_t));
}

// Helper to see if the identifier in a buffer has the expected value.
inline bool BufferHasIdentifier(const void* buf, const char* identifier,
                                bool size_prefixed = false)
{
  return strncmp(GetBufferIdentifier(buf, size_prefixed), identifier,
                 FlatBufferBuilder::kFileIdentifierLength) == 0;
}

// Helper class to verify the integrity of a FlatBuffer
class Verifier FLATBUFFERS_FINAL_CLASS
{
public:
  Verifier(const uint8_t* buf, size_t buf_len, uoffset_t _max_depth = 64,
           uoffset_t _max_tables = 1000000, bool _check_alignment = true) :
    buf_(buf),
    size_(buf_len),
    depth_(0),
    max_depth_(_max_depth),
    num_tables_(0),
    max_tables_(_max_tables),
    upper_bound_(0),
    check_alignment_(_check_alignment)
  {
    FLATBUFFERS_ASSERT(size_ < FLATBUFFERS_MAX_BUFFER_SIZE);
  }

  // Central location where any verification failures register.
  bool Check(bool ok) const
  {
    // clang-format off
    #ifdef FLATBUFFERS_DEBUG_VERIFICATION_FAILURE
      FLATBUFFERS_ASSERT(ok);
    #endif
    #ifdef FLATBUFFERS_TRACK_VERIFIER_BUFFER_SIZE
      if (!ok)
        upper_bound_ = 0;
    #endif
    // clang-format on
    return ok;
  }

  // Verify any range within the buffer.
  bool Verify(size_t elem, size_t elem_len) const
  {
    // clang-format off
    #ifdef FLATBUFFERS_TRACK_VERIFIER_BUFFER_SIZE
      auto upper_bound = elem + elem_len;
      if (upper_bound_ < upper_bound)
        upper_bound_ =  upper_bound;
    #endif
    // clang-format on
    return Check(elem_len < size_ && elem <= size_ - elem_len);
  }

  template <typename T>
  bool VerifyAlignment(size_t elem) const
  {
    return Check((elem & (sizeof(T) - 1)) == 0 || !check_alignment_);
  }

  // Verify a range indicated by sizeof(T).
  template <typename T>
  bool Verify(size_t elem) const
  {
    return VerifyAlignment<T>(elem) && Verify(elem, sizeof(T));
  }

  bool VerifyFromPointer(const uint8_t* p, size_t len)
  {
    auto o = static_cast<size_t>(p - buf_);
    return Verify(o, len);
  }

  // Verify relative to a known-good base pointer.
  bool Verify(const uint8_t* base, voffset_t elem_off, size_t elem_len) const
  {
    return Verify(static_cast<size_t>(base - buf_) + elem_off, elem_len);
  }

  template <typename T>
  bool Verify(const uint8_t* base, voffset_t elem_off) const
  {
    return Verify(static_cast<size_t>(base - buf_) + elem_off, sizeof(T));
  }

  // Verify a pointer (may be NULL) of a table type.
  template <typename T>
  bool VerifyTable(const T* table)
  {
    return !table || table->Verify(*this);
  }

  // Verify a pointer (may be NULL) of any vector type.
  template <typename T>
  bool VerifyVector(const Vector<T>* vec) const
  {
    return !vec || VerifyVectorOrString(reinterpret_cast<const uint8_t*>(vec), sizeof(T));
  }

  // Verify a pointer (may be NULL) of a vector to struct.
  template <typename T>
  bool VerifyVector(const Vector<const T*>* vec) const
  {
    return VerifyVector(reinterpret_cast<const Vector<T>*>(vec));
  }

  // Verify a pointer (may be NULL) to string.
  bool VerifyString(const String* str) const
  {
    size_t end;
    return !str ||
           (VerifyVectorOrString(reinterpret_cast<const uint8_t*>(str), 1, &end) &&
            Verify(end, 1) &&            // Must have terminator
            Check(buf_[end] == '\0'));   // Terminating byte must be 0.
  }

  // Common code between vectors and strings.
  bool VerifyVectorOrString(const uint8_t* vec, size_t elem_size,
                            size_t* end = nullptr) const
  {
    auto veco = static_cast<size_t>(vec - buf_);
    // Check we can read the size field.
    if (!Verify<uoffset_t>(veco))
      return false;
    // Check the whole array. If this is a string, the byte past the array
    // must be 0.
    auto size = ReadScalar<uoffset_t>(vec);
    auto max_elems = FLATBUFFERS_MAX_BUFFER_SIZE / elem_size;
    if (!Check(size < max_elems))
      return false;   // Protect against byte_size overflowing.
    auto byte_size = sizeof(size) + elem_size * size;
    if (end)
      *end = veco + byte_size;
    return Verify(veco, byte_size);
  }

  // Special case for string contents, after the above has been called.
  bool VerifyVectorOfStrings(const Vector<Offset<String>>* vec) const
  {
    if (vec)
    {
      for (uoffset_t i = 0; i < vec->size(); i++)
      {
        if (!VerifyString(vec->Get(i)))
          return false;
      }
    }
    return true;
  }

  // Special case for table contents, after the above has been called.
  template <typename T>
  bool VerifyVectorOfTables(const Vector<Offset<T>>* vec)
  {
    if (vec)
    {
      for (uoffset_t i = 0; i < vec->size(); i++)
      {
        if (!vec->Get(i)->Verify(*this))
          return false;
      }
    }
    return true;
  }

  __supress_ubsan__("unsigned-integer-overflow") bool VerifyTableStart(
      const uint8_t* table)
  {
    // Check the vtable offset.
    auto tableo = static_cast<size_t>(table - buf_);
    if (!Verify<soffset_t>(tableo))
      return false;
    // This offset may be signed, but doing the subtraction unsigned always
    // gives the result we want.
    auto vtableo = tableo - static_cast<size_t>(ReadScalar<soffset_t>(table));
    // Check the vtable size field, then check vtable fits in its entirety.
    return VerifyComplexity() && Verify<voffset_t>(vtableo) &&
           VerifyAlignment<voffset_t>(ReadScalar<voffset_t>(buf_ + vtableo)) &&
           Verify(vtableo, ReadScalar<voffset_t>(buf_ + vtableo));
  }

  template <typename T>
  bool VerifyBufferFromStart(const char* identifier, size_t start)
  {
    if (identifier && !Check((size_ >= 2 * sizeof(flatbuffers::uoffset_t) &&
                              BufferHasIdentifier(buf_ + start, identifier))))
    {
      return false;
    }

    // Call T::Verify, which must be in the generated code for this type.
    auto o = VerifyOffset(start);
    return o && reinterpret_cast<const T*>(buf_ + start + o)->Verify(*this)
    // clang-format off
    #ifdef FLATBUFFERS_TRACK_VERIFIER_BUFFER_SIZE
           && GetComputedSize()
    #endif
        ;
    // clang-format on
  }

  // Verify this whole buffer, starting with root type T.
  template <typename T>
  bool VerifyBuffer()
  {
    return VerifyBuffer<T>(nullptr);
  }

  template <typename T>
  bool VerifyBuffer(const char* identifier)
  {
    return VerifyBufferFromStart<T>(identifier, 0);
  }

  template <typename T>
  bool VerifySizePrefixedBuffer(const char* identifier)
  {
    return Verify<uoffset_t>(0U) &&
           ReadScalar<uoffset_t>(buf_) == size_ - sizeof(uoffset_t) &&
           VerifyBufferFromStart<T>(identifier, sizeof(uoffset_t));
  }

  uoffset_t VerifyOffset(size_t start) const
  {
    if (!Verify<uoffset_t>(start))
      return 0;
    auto o = ReadScalar<uoffset_t>(buf_ + start);
    // May not point to itself.
    if (!Check(o != 0))
      return 0;
    // Can't wrap around / buffers are max 2GB.
    if (!Check(static_cast<soffset_t>(o) >= 0))
      return 0;
    // Must be inside the buffer to create a pointer from it (pointer outside
    // buffer is UB).
    if (!Verify(start + o, 1))
      return 0;
    return o;
  }

  uoffset_t VerifyOffset(const uint8_t* base, voffset_t start) const
  {
    return VerifyOffset(static_cast<size_t>(base - buf_) + start);
  }

  // Called at the start of a table to increase counters measuring data
  // structure depth and amount, and possibly bails out with false if
  // limits set by the constructor have been hit. Needs to be balanced
  // with EndTable().
  bool VerifyComplexity()
  {
    depth_++;
    num_tables_++;
    return Check(depth_ <= max_depth_ && num_tables_ <= max_tables_);
  }

  // Called at the end of a table to pop the depth count.
  bool EndTable()
  {
    depth_--;
    return true;
  }

  // Returns the message size in bytes
  size_t GetComputedSize() const
  {
    // clang-format off
    #ifdef FLATBUFFERS_TRACK_VERIFIER_BUFFER_SIZE
      uintptr_t size = upper_bound_;
      // Align the size to uoffset_t
      size = (size - 1 + sizeof(uoffset_t)) & ~(sizeof(uoffset_t) - 1);
      return (size > size_) ?  0 : size;
    #else
      // Must turn on FLATBUFFERS_TRACK_VERIFIER_BUFFER_SIZE for this to work.
      (void)upper_bound_;
      FLATBUFFERS_ASSERT(false);
      return 0;
    #endif
    // clang-format on
  }

private:
  const uint8_t* buf_;
  size_t size_;
  uoffset_t depth_;
  uoffset_t max_depth_;
  uoffset_t num_tables_;
  uoffset_t max_tables_;
  mutable size_t upper_bound_;
  bool check_alignment_;
};

// Convenient way to bundle a buffer and its length, to pass it around
// typed by its root.
// A BufferRef does not own its buffer.
struct BufferRefBase
{
};   // for std::is_base_of
template <typename T>
struct BufferRef : BufferRefBase
{
  BufferRef() : buf(nullptr), len(0), must_free(false)
  {}
  BufferRef(uint8_t* _buf, uoffset_t _len) : buf(_buf), len(_len), must_free(false)
  {}

  ~BufferRef()
  {
    if (must_free)
      free(buf);
  }

  const T* GetRoot() const
  {
    return flatbuffers::GetRoot<T>(buf);
  }

  bool Verify()
  {
    Verifier verifier(buf, len);
    return verifier.VerifyBuffer<T>(nullptr);
  }

  uint8_t* buf;
  uoffset_t len;
  bool must_free;
};

// "structs" are flat structures that do not have an offset table, thus
// always have all members present and do not support forwards/backwards
// compatible extensions.

class Struct FLATBUFFERS_FINAL_CLASS
{
public:
  template <typename T>
  T GetField(uoffset_t o) const
  {
    return ReadScalar<T>(&data_[o]);
  }

  template <typename T>
  T GetStruct(uoffset_t o) const
  {
    return reinterpret_cast<T>(&data_[o]);
  }

  const uint8_t* GetAddressOf(uoffset_t o) const
  {
    return &data_[o];
  }
  uint8_t* GetAddressOf(uoffset_t o)
  {
    return &data_[o];
  }

private:
  // private constructor & copy constructor: you obtain instances of this
  // class by pointing to existing data only
  Struct();
  Struct(const Struct&);
  Struct& operator=(const Struct&);

  uint8_t data_[1];
};

// "tables" use an offset table (possibly shared) that allows fields to be
// omitted and added at will, but uses an extra indirection to read.
class Table
{
public:
  const uint8_t* GetVTable() const
  {
    return data_ - ReadScalar<soffset_t>(data_);
  }

  // This gets the field offset for any of the functions below it, or 0
  // if the field was not present.
  voffset_t GetOptionalFieldOffset(voffset_t field) const
  {
    // The vtable offset is always at the start.
    auto vtable = GetVTable();
    // The first element is the size of the vtable (fields + type id + itself).
    auto vtsize = ReadScalar<voffset_t>(vtable);
    // If the field we're accessing is outside the vtable, we're reading older
    // data, so it's the same as if the offset was 0 (not present).
    return field < vtsize ? ReadScalar<voffset_t>(vtable + field) : 0;
  }

  template <typename T>
  T GetField(voffset_t field, T defaultval) const
  {
    auto field_offset = GetOptionalFieldOffset(field);
    return field_offset ? ReadScalar<T>(data_ + field_offset) : defaultval;
  }

  template <typename P>
  P GetPointer(voffset_t field)
  {
    auto field_offset = GetOptionalFieldOffset(field);
    auto p = data_ + field_offset;
    return field_offset ? reinterpret_cast<P>(p + ReadScalar<uoffset_t>(p)) : nullptr;
  }
  template <typename P>
  P GetPointer(voffset_t field) const
  {
    return const_cast<Table*>(this)->GetPointer<P>(field);
  }

  template <typename P>
  P GetStruct(voffset_t field) const
  {
    auto field_offset = GetOptionalFieldOffset(field);
    auto p = const_cast<uint8_t*>(data_ + field_offset);
    return field_offset ? reinterpret_cast<P>(p) : nullptr;
  }

  template <typename Raw, typename Face>
  flatbuffers::Optional<Face> GetOptional(voffset_t field) const
  {
    auto field_offset = GetOptionalFieldOffset(field);
    auto p = data_ + field_offset;
    return field_offset ? Optional<Face>(static_cast<Face>(ReadScalar<Raw>(p))) :
                          Optional<Face>();
  }

  template <typename T>
  bool SetField(voffset_t field, T val, T def)
  {
    auto field_offset = GetOptionalFieldOffset(field);
    if (!field_offset)
      return IsTheSameAs(val, def);
    WriteScalar(data_ + field_offset, val);
    return true;
  }
  template <typename T>
  bool SetField(voffset_t field, T val)
  {
    auto field_offset = GetOptionalFieldOffset(field);
    if (!field_offset)
      return false;
    WriteScalar(data_ + field_offset, val);
    return true;
  }

  bool SetPointer(voffset_t field, const uint8_t* val)
  {
    auto field_offset = GetOptionalFieldOffset(field);
    if (!field_offset)
      return false;
    WriteScalar(data_ + field_offset,
                static_cast<uoffset_t>(val - (data_ + field_offset)));
    return true;
  }

  uint8_t* GetAddressOf(voffset_t field)
  {
    auto field_offset = GetOptionalFieldOffset(field);
    return field_offset ? data_ + field_offset : nullptr;
  }
  const uint8_t* GetAddressOf(voffset_t field) const
  {
    return const_cast<Table*>(this)->GetAddressOf(field);
  }

  bool CheckField(voffset_t field) const
  {
    return GetOptionalFieldOffset(field) != 0;
  }

  // Verify the vtable of this table.
  // Call this once per table, followed by VerifyField once per field.
  bool VerifyTableStart(Verifier& verifier) const
  {
    return verifier.VerifyTableStart(data_);
  }

  // Verify a particular field.
  template <typename T>
  bool VerifyField(const Verifier& verifier, voffset_t field) const
  {
    // Calling GetOptionalFieldOffset should be safe now thanks to
    // VerifyTable().
    auto field_offset = GetOptionalFieldOffset(field);
    // Check the actual field.
    return !field_offset || verifier.Verify<T>(data_, field_offset);
  }

  // VerifyField for required fields.
  template <typename T>
  bool VerifyFieldRequired(const Verifier& verifier, voffset_t field) const
  {
    auto field_offset = GetOptionalFieldOffset(field);
    return verifier.Check(field_offset != 0) && verifier.Verify<T>(data_, field_offset);
  }

  // Versions for offsets.
  bool VerifyOffset(const Verifier& verifier, voffset_t field) const
  {
    auto field_offset = GetOptionalFieldOffset(field);
    return !field_offset || verifier.VerifyOffset(data_, field_offset);
  }

  bool VerifyOffsetRequired(const Verifier& verifier, voffset_t field) const
  {
    auto field_offset = GetOptionalFieldOffset(field);
    return verifier.Check(field_offset != 0) &&
           verifier.VerifyOffset(data_, field_offset);
  }

private:
  // private constructor & copy constructor: you obtain instances of this
  // class by pointing to existing data only
  Table();
  Table(const Table& other);
  Table& operator=(const Table&);

  uint8_t data_[1];
};

// This specialization allows avoiding warnings like:
// MSVC C4800: type: forcing value to bool 'true' or 'false'.
template <>
inline flatbuffers::Optional<bool>
Table::GetOptional<uint8_t, bool>(voffset_t field) const
{
  auto field_offset = GetOptionalFieldOffset(field);
  auto p = data_ + field_offset;
  return field_offset ? Optional<bool>(ReadScalar<uint8_t>(p) != 0) : Optional<bool>();
}

template <typename T>
void FlatBufferBuilder::Required(Offset<T> table, voffset_t field)
{
  auto table_ptr = reinterpret_cast<const Table*>(buf_.data_at(table.o));
  bool ok = table_ptr->GetOptionalFieldOffset(field) != 0;
  // If this fails, the caller will show what field needs to be set.
  FLATBUFFERS_ASSERT(ok);
  (void)ok;
}

inline const uint8_t* GetBufferStartFromRootPointer(const void* root)
{
  auto table = reinterpret_cast<const Table*>(root);
  auto vtable = table->GetVTable();
  // Either the vtable is before the root or after the root.
  auto start = (std::min)(vtable, reinterpret_cast<const uint8_t*>(root));
  // Align to at least sizeof(uoffset_t).
  start = reinterpret_cast<const uint8_t*>(reinterpret_cast<uintptr_t>(start) &
                                           ~(sizeof(uoffset_t) - 1));
  // Additionally, there may be a file_identifier in the buffer, and the root
  // offset. The buffer may have been aligned to any size between
  // sizeof(uoffset_t) and FLATBUFFERS_MAX_ALIGNMENT (see "force_align").
  // Sadly, the exact alignment is only known when constructing the buffer,
  // since it depends on the presence of values with said alignment properties.
  // So instead, we simply look at the next uoffset_t values (root,
  // file_identifier, and alignment padding) to see which points to the root.
  // None of the other values can "impersonate" the root since they will either
  // be 0 or four ASCII characters.
  static_assert(FlatBufferBuilder::kFileIdentifierLength == sizeof(uoffset_t), "file_"
                                                                               "identifie"
                                                                               "r "
                                                                               "is "
                                                                               "assumed "
                                                                               "to be "
                                                                               "the same "
                                                                               "size as "
                                                                               "uoffset_"
                                                                               "t");
  for (auto possible_roots = FLATBUFFERS_MAX_ALIGNMENT / sizeof(uoffset_t) + 1;
       possible_roots; possible_roots--)
  {
    start -= sizeof(uoffset_t);
    if (ReadScalar<uoffset_t>(start) + start == reinterpret_cast<const uint8_t*>(root))
      return start;
  }
  // We didn't find the root, either the "root" passed isn't really a root,
  // or the buffer is corrupt.
  // Assert, because calling this function with bad data may cause reads
  // outside of buffer boundaries.
  FLATBUFFERS_ASSERT(false);
  return nullptr;
}

inline uoffset_t GetPrefixedSize(const uint8_t* buf)
{
  return ReadScalar<uoffset_t>(buf);
}

// Base class for native objects (FlatBuffer data de-serialized into native
// C++ data structures).
// Contains no functionality, purely documentative.
struct NativeTable
{
};

typedef uint64_t hash_value_t;
// clang-format off
#ifdef FLATBUFFERS_CPP98_STL
  typedef void (*resolver_function_t)(void **pointer_adr, hash_value_t hash);
  typedef hash_value_t (*rehasher_function_t)(void *pointer);
#else
  typedef std::function<void (void **pointer_adr, hash_value_t hash)>
          resolver_function_t;
  typedef std::function<hash_value_t (void *pointer)> rehasher_function_t;
#endif
// clang-format on

// Helper function to test if a field is present, using any of the field
// enums in the generated code.
// `table` must be a generated table type. Since this is a template parameter,
// this is not typechecked to be a subclass of Table, so beware!
// Note: this function will return false for fields equal to the default
// value, since they're not stored in the buffer (unless force_defaults was
// used).
template <typename T>
bool IsFieldPresent(const T* table, typename T::FlatBuffersVTableOffset field)
{
  // Cast, since Table is a private baseclass of any table types.
  return reinterpret_cast<const Table*>(table)->CheckField(static_cast<voffset_t>(field));
}

// Utility function for reverse lookups on the EnumNames*() functions
// (in the generated C++ code)
// names must be NULL terminated.
inline int LookupEnum(const char** names, const char* name)
{
  for (const char** p = names; *p; p++)
    if (!strcmp(*p, name))
      return static_cast<int>(p - names);
  return -1;
}

// These macros allow us to layout a struct with a guarantee that they'll end
// up looking the same on different compilers and platforms.
// It does this by disallowing the compiler to do any padding, and then
// does padding itself by inserting extra padding fields that make every
// element aligned to its own size.
// Additionally, it manually sets the alignment of the struct as a whole,
// which is typically its largest element, or a custom size set in the schema
// by the force_align attribute.
// These are used in the generated code only.

// clang-format off
#if defined(_MSC_VER)
  #define FLATBUFFERS_MANUALLY_ALIGNED_STRUCT(alignment) \
    __pragma(pack(1)) \
    struct __declspec(align(alignment))
  #define FLATBUFFERS_STRUCT_END(name, size) \
    __pragma(pack()) \
    static_assert(sizeof(name) == size, "compiler breaks packing rules")
#elif defined(__GNUC__) || defined(__clang__) || defined(__ICCARM__)
  #define FLATBUFFERS_MANUALLY_ALIGNED_STRUCT(alignment) \
    _Pragma("pack(1)") \
    struct __attribute__((aligned(alignment)))
  #define FLATBUFFERS_STRUCT_END(name, size) \
    _Pragma("pack()") \
    static_assert(sizeof(name) == size, "compiler breaks packing rules")
#else
  #error Unknown compiler, please define structure alignment macros
#endif
// clang-format on

// Minimal reflection via code generation.
// Besides full-fat reflection (see reflection.h) and parsing/printing by
// loading schemas (see idl.h), we can also have code generation for mimimal
// reflection data which allows pretty-printing and other uses without needing
// a schema or a parser.
// Generate code with --reflect-types (types only) or --reflect-names (names
// also) to enable.
// See minireflect.h for utilities using this functionality.

// These types are organized slightly differently as the ones in idl.h.
enum SequenceType
{
  ST_TABLE,
  ST_STRUCT,
  ST_UNION,
  ST_ENUM
};

// Scalars have the same order as in idl.h
// clang-format off
#define FLATBUFFERS_GEN_ELEMENTARY_TYPES(ET) \
  ET(ET_UTYPE) \
  ET(ET_BOOL) \
  ET(ET_CHAR) \
  ET(ET_UCHAR) \
  ET(ET_SHORT) \
  ET(ET_USHORT) \
  ET(ET_INT) \
  ET(ET_UINT) \
  ET(ET_LONG) \
  ET(ET_ULONG) \
  ET(ET_FLOAT) \
  ET(ET_DOUBLE) \
  ET(ET_STRING) \
  ET(ET_SEQUENCE)  // See SequenceType.

enum ElementaryType {
  #define FLATBUFFERS_ET(E) E,
    FLATBUFFERS_GEN_ELEMENTARY_TYPES(FLATBUFFERS_ET)
  #undef FLATBUFFERS_ET
};

inline const char * const *ElementaryTypeNames() {
  static const char * const names[] = {
    #define FLATBUFFERS_ET(E) #E,
      FLATBUFFERS_GEN_ELEMENTARY_TYPES(FLATBUFFERS_ET)
    #undef FLATBUFFERS_ET
  };
  return names;
}
// clang-format on

// Basic type info cost just 16bits per field!
// We're explicitly defining the signedness since the signedness of integer
// bitfields is otherwise implementation-defined and causes warnings on older
// GCC compilers.
struct TypeCode
{
  // ElementaryType
  unsigned short base_type : 4;
  // Either vector (in table) or array (in struct)
  unsigned short is_repeating : 1;
  // Index into type_refs below, or -1 for none.
  signed short sequence_ref : 11;
};

static_assert(sizeof(TypeCode) == 2, "TypeCode");

struct TypeTable;

// Signature of the static method present in each type.
typedef const TypeTable* (*TypeFunction)();

struct TypeTable
{
  SequenceType st;
  size_t num_elems;                // of type_codes, values, names (but not type_refs).
  const TypeCode* type_codes;      // num_elems count
  const TypeFunction* type_refs;   // less than num_elems entries (see TypeCode).
  const int16_t* array_sizes;      // less than num_elems entries (see TypeCode).
  const int64_t* values;           // Only set for non-consecutive enum/union or structs.
  const char* const* names;        // Only set if compiled with --reflect-names.
};

// String which identifies the current version of FlatBuffers.
// flatbuffer_version_string is used by Google developers to identify which
// applications uploaded to Google Play are using this library.  This allows
// the development team at Google to determine the popularity of the library.
// How it works: Applications that are uploaded to the Google Play Store are
// scanned for this version string.  We track which applications are using it
// to measure popularity.  You are free to remove it (of course) but we would
// appreciate if you left it in.

// Weak linkage is culled by VS & doesn't work on cygwin.
// clang-format off
#if !defined(_WIN32) && !defined(__CYGWIN__)

extern volatile __attribute__((weak)) const char *flatbuffer_version_string;
volatile __attribute__((weak)) const char *flatbuffer_version_string =
  "FlatBuffers "
  FLATBUFFERS_STRING(FLATBUFFERS_VERSION_MAJOR) "."
  FLATBUFFERS_STRING(FLATBUFFERS_VERSION_MINOR) "."
  FLATBUFFERS_STRING(FLATBUFFERS_VERSION_REVISION);

#endif  // !defined(_WIN32) && !defined(__CYGWIN__)

#define FLATBUFFERS_DEFINE_BITMASK_OPERATORS(E, T)\
    inline E operator | (E lhs, E rhs){\
        return E(T(lhs) | T(rhs));\
    }\
    inline E operator & (E lhs, E rhs){\
        return E(T(lhs) & T(rhs));\
    }\
    inline E operator ^ (E lhs, E rhs){\
        return E(T(lhs) ^ T(rhs));\
    }\
    inline E operator ~ (E lhs){\
        return E(~T(lhs));\
    }\
    inline E operator |= (E &lhs, E rhs){\
        lhs = lhs | rhs;\
        return lhs;\
    }\
    inline E operator &= (E &lhs, E rhs){\
        lhs = lhs & rhs;\
        return lhs;\
    }\
    inline E operator ^= (E &lhs, E rhs){\
        lhs = lhs ^ rhs;\
        return lhs;\
    }\
    inline bool operator !(E rhs) \
    {\
        return !bool(T(rhs)); \
    }
}  // namespace flatbuffers

// clang-format on

#endif   // FLATBUFFERS_H_