diff --git a/include/flatbuffers/flexbuffers.h b/include/flatbuffers/flexbuffers.h
new file mode 100644
index 0000000..7cba5b7
--- /dev/null
+++ b/include/flatbuffers/flexbuffers.h
@@ -0,0 +1,1538 @@
+/*
+ * Copyright 2017 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_FLEXBUFFERS_H_
+#define FLATBUFFERS_FLEXBUFFERS_H_
+
+#include <map>
+// Used to select STL variant.
+#include "flatbuffers/base.h"
+// We use the basic binary writing functions from the regular FlatBuffers.
+#include "flatbuffers/util.h"
+
+#ifdef _MSC_VER
+#  include <intrin.h>
+#endif
+
+#if defined(_MSC_VER)
+#  pragma warning(push)
+#  pragma warning(disable : 4127)  // C4127: conditional expression is constant
+#endif
+
+namespace flexbuffers {
+
+class Reference;
+class Map;
+
+// These are used in the lower 2 bits of a type field to determine the size of
+// the elements (and or size field) of the item pointed to (e.g. vector).
+enum BitWidth {
+  BIT_WIDTH_8 = 0,
+  BIT_WIDTH_16 = 1,
+  BIT_WIDTH_32 = 2,
+  BIT_WIDTH_64 = 3,
+};
+
+// These are used as the upper 6 bits of a type field to indicate the actual
+// type.
+enum Type {
+  FBT_NULL = 0,
+  FBT_INT = 1,
+  FBT_UINT = 2,
+  FBT_FLOAT = 3,
+  // Types above stored inline, types below store an offset.
+  FBT_KEY = 4,
+  FBT_STRING = 5,
+  FBT_INDIRECT_INT = 6,
+  FBT_INDIRECT_UINT = 7,
+  FBT_INDIRECT_FLOAT = 8,
+  FBT_MAP = 9,
+  FBT_VECTOR = 10,      // Untyped.
+  FBT_VECTOR_INT = 11,  // Typed any size (stores no type table).
+  FBT_VECTOR_UINT = 12,
+  FBT_VECTOR_FLOAT = 13,
+  FBT_VECTOR_KEY = 14,
+  FBT_VECTOR_STRING = 15,
+  FBT_VECTOR_INT2 = 16,  // Typed tuple (no type table, no size field).
+  FBT_VECTOR_UINT2 = 17,
+  FBT_VECTOR_FLOAT2 = 18,
+  FBT_VECTOR_INT3 = 19,  // Typed triple (no type table, no size field).
+  FBT_VECTOR_UINT3 = 20,
+  FBT_VECTOR_FLOAT3 = 21,
+  FBT_VECTOR_INT4 = 22,  // Typed quad (no type table, no size field).
+  FBT_VECTOR_UINT4 = 23,
+  FBT_VECTOR_FLOAT4 = 24,
+  FBT_BLOB = 25,
+  FBT_BOOL = 26,
+  FBT_VECTOR_BOOL =
+      36,  // To Allow the same type of conversion of type to vector type
+};
+
+inline bool IsInline(Type t) { return t <= FBT_FLOAT || t == FBT_BOOL; }
+
+inline bool IsTypedVectorElementType(Type t) {
+  return (t >= FBT_INT && t <= FBT_STRING) || t == FBT_BOOL;
+}
+
+inline bool IsTypedVector(Type t) {
+  return (t >= FBT_VECTOR_INT && t <= FBT_VECTOR_STRING) ||
+         t == FBT_VECTOR_BOOL;
+}
+
+inline bool IsFixedTypedVector(Type t) {
+  return t >= FBT_VECTOR_INT2 && t <= FBT_VECTOR_FLOAT4;
+}
+
+inline Type ToTypedVector(Type t, size_t fixed_len = 0) {
+  FLATBUFFERS_ASSERT(IsTypedVectorElementType(t));
+  switch (fixed_len) {
+    case 0: return static_cast<Type>(t - FBT_INT + FBT_VECTOR_INT);
+    case 2: return static_cast<Type>(t - FBT_INT + FBT_VECTOR_INT2);
+    case 3: return static_cast<Type>(t - FBT_INT + FBT_VECTOR_INT3);
+    case 4: return static_cast<Type>(t - FBT_INT + FBT_VECTOR_INT4);
+    default: FLATBUFFERS_ASSERT(0); return FBT_NULL;
+  }
+}
+
+inline Type ToTypedVectorElementType(Type t) {
+  FLATBUFFERS_ASSERT(IsTypedVector(t));
+  return static_cast<Type>(t - FBT_VECTOR_INT + FBT_INT);
+}
+
+inline Type ToFixedTypedVectorElementType(Type t, uint8_t *len) {
+  FLATBUFFERS_ASSERT(IsFixedTypedVector(t));
+  auto fixed_type = t - FBT_VECTOR_INT2;
+  *len = static_cast<uint8_t>(fixed_type / 3 +
+                              2);  // 3 types each, starting from length 2.
+  return static_cast<Type>(fixed_type % 3 + FBT_INT);
+}
+
+// TODO: implement proper support for 8/16bit floats, or decide not to
+// support them.
+typedef int16_t half;
+typedef int8_t quarter;
+
+// TODO: can we do this without conditionals using intrinsics or inline asm
+// on some platforms? Given branch prediction the method below should be
+// decently quick, but it is the most frequently executed function.
+// We could do an (unaligned) 64-bit read if we ifdef out the platforms for
+// which that doesn't work (or where we'd read into un-owned memory).
+template<typename R, typename T1, typename T2, typename T4, typename T8>
+R ReadSizedScalar(const uint8_t *data, uint8_t byte_width) {
+  return byte_width < 4
+             ? (byte_width < 2
+                    ? static_cast<R>(flatbuffers::ReadScalar<T1>(data))
+                    : static_cast<R>(flatbuffers::ReadScalar<T2>(data)))
+             : (byte_width < 8
+                    ? static_cast<R>(flatbuffers::ReadScalar<T4>(data))
+                    : static_cast<R>(flatbuffers::ReadScalar<T8>(data)));
+}
+
+inline int64_t ReadInt64(const uint8_t *data, uint8_t byte_width) {
+  return ReadSizedScalar<int64_t, int8_t, int16_t, int32_t, int64_t>(
+      data, byte_width);
+}
+
+inline uint64_t ReadUInt64(const uint8_t *data, uint8_t byte_width) {
+  // This is the "hottest" function (all offset lookups use this), so worth
+  // optimizing if possible.
+  // TODO: GCC apparently replaces memcpy by a rep movsb, but only if count is a
+  // constant, which here it isn't. Test if memcpy is still faster than
+  // the conditionals in ReadSizedScalar. Can also use inline asm.
+  // clang-format off
+  #if defined(_MSC_VER) && (defined(_M_X64) || defined _M_IX86)
+    uint64_t u = 0;
+    __movsb(reinterpret_cast<uint8_t *>(&u),
+            reinterpret_cast<const uint8_t *>(data), byte_width);
+    return flatbuffers::EndianScalar(u);
+  #else
+    return ReadSizedScalar<uint64_t, uint8_t, uint16_t, uint32_t, uint64_t>(
+             data, byte_width);
+  #endif
+  // clang-format on
+}
+
+inline double ReadDouble(const uint8_t *data, uint8_t byte_width) {
+  return ReadSizedScalar<double, quarter, half, float, double>(data,
+                                                               byte_width);
+}
+
+inline const uint8_t *Indirect(const uint8_t *offset, uint8_t byte_width) {
+  return offset - ReadUInt64(offset, byte_width);
+}
+
+template<typename T> const uint8_t *Indirect(const uint8_t *offset) {
+  return offset - flatbuffers::ReadScalar<T>(offset);
+}
+
+inline BitWidth WidthU(uint64_t u) {
+#define FLATBUFFERS_GET_FIELD_BIT_WIDTH(value, width)                   \
+  {                                                                     \
+    if (!((u) & ~((1ULL << (width)) - 1ULL))) return BIT_WIDTH_##width; \
+  }
+  FLATBUFFERS_GET_FIELD_BIT_WIDTH(u, 8);
+  FLATBUFFERS_GET_FIELD_BIT_WIDTH(u, 16);
+  FLATBUFFERS_GET_FIELD_BIT_WIDTH(u, 32);
+#undef FLATBUFFERS_GET_FIELD_BIT_WIDTH
+  return BIT_WIDTH_64;
+}
+
+inline BitWidth WidthI(int64_t i) {
+  auto u = static_cast<uint64_t>(i) << 1;
+  return WidthU(i >= 0 ? u : ~u);
+}
+
+inline BitWidth WidthF(double f) {
+  return static_cast<double>(static_cast<float>(f)) == f ? BIT_WIDTH_32
+                                                         : BIT_WIDTH_64;
+}
+
+// Base class of all types below.
+// Points into the data buffer and allows access to one type.
+class Object {
+ public:
+  Object(const uint8_t *data, uint8_t byte_width)
+      : data_(data), byte_width_(byte_width) {}
+
+ protected:
+  const uint8_t *data_;
+  uint8_t byte_width_;
+};
+
+// Stores size in `byte_width_` bytes before data_ pointer.
+class Sized : public Object {
+ public:
+  Sized(const uint8_t *data, uint8_t byte_width) : Object(data, byte_width) {}
+  size_t size() const {
+    return static_cast<size_t>(ReadUInt64(data_ - byte_width_, byte_width_));
+  }
+};
+
+class String : public Sized {
+ public:
+  String(const uint8_t *data, uint8_t byte_width) : Sized(data, byte_width) {}
+
+  size_t length() const { return size(); }
+  const char *c_str() const { return reinterpret_cast<const char *>(data_); }
+  std::string str() const { return std::string(c_str(), length()); }
+
+  static String EmptyString() {
+    static const uint8_t empty_string[] = { 0 /*len*/, 0 /*terminator*/ };
+    return String(empty_string + 1, 1);
+  }
+  bool IsTheEmptyString() const { return data_ == EmptyString().data_; }
+};
+
+class Blob : public Sized {
+ public:
+  Blob(const uint8_t *data_buf, uint8_t byte_width)
+      : Sized(data_buf, byte_width) {}
+
+  static Blob EmptyBlob() {
+    static const uint8_t empty_blob[] = { 0 /*len*/ };
+    return Blob(empty_blob + 1, 1);
+  }
+  bool IsTheEmptyBlob() const { return data_ == EmptyBlob().data_; }
+  const uint8_t *data() const { return data_; }
+};
+
+class Vector : public Sized {
+ public:
+  Vector(const uint8_t *data, uint8_t byte_width) : Sized(data, byte_width) {}
+
+  Reference operator[](size_t i) const;
+
+  static Vector EmptyVector() {
+    static const uint8_t empty_vector[] = { 0 /*len*/ };
+    return Vector(empty_vector + 1, 1);
+  }
+  bool IsTheEmptyVector() const { return data_ == EmptyVector().data_; }
+};
+
+class TypedVector : public Sized {
+ public:
+  TypedVector(const uint8_t *data, uint8_t byte_width, Type element_type)
+      : Sized(data, byte_width), type_(element_type) {}
+
+  Reference operator[](size_t i) const;
+
+  static TypedVector EmptyTypedVector() {
+    static const uint8_t empty_typed_vector[] = { 0 /*len*/ };
+    return TypedVector(empty_typed_vector + 1, 1, FBT_INT);
+  }
+  bool IsTheEmptyVector() const {
+    return data_ == TypedVector::EmptyTypedVector().data_;
+  }
+
+  Type ElementType() { return type_; }
+
+ private:
+  Type type_;
+
+  friend Map;
+};
+
+class FixedTypedVector : public Object {
+ public:
+  FixedTypedVector(const uint8_t *data, uint8_t byte_width, Type element_type,
+                   uint8_t len)
+      : Object(data, byte_width), type_(element_type), len_(len) {}
+
+  Reference operator[](size_t i) const;
+
+  static FixedTypedVector EmptyFixedTypedVector() {
+    static const uint8_t fixed_empty_vector[] = { 0 /* unused */ };
+    return FixedTypedVector(fixed_empty_vector, 1, FBT_INT, 0);
+  }
+  bool IsTheEmptyFixedTypedVector() const {
+    return data_ == FixedTypedVector::EmptyFixedTypedVector().data_;
+  }
+
+  Type ElementType() { return type_; }
+  uint8_t size() { return len_; }
+
+ private:
+  Type type_;
+  uint8_t len_;
+};
+
+class Map : public Vector {
+ public:
+  Map(const uint8_t *data, uint8_t byte_width) : Vector(data, byte_width) {}
+
+  Reference operator[](const char *key) const;
+  Reference operator[](const std::string &key) const;
+
+  Vector Values() const { return Vector(data_, byte_width_); }
+
+  TypedVector Keys() const {
+    const size_t num_prefixed_fields = 3;
+    auto keys_offset = data_ - byte_width_ * num_prefixed_fields;
+    return TypedVector(Indirect(keys_offset, byte_width_),
+                       static_cast<uint8_t>(
+                           ReadUInt64(keys_offset + byte_width_, byte_width_)),
+                       FBT_KEY);
+  }
+
+  static Map EmptyMap() {
+    static const uint8_t empty_map[] = {
+      0 /*keys_len*/, 0 /*keys_offset*/, 1 /*keys_width*/, 0 /*len*/
+    };
+    return Map(empty_map + 4, 1);
+  }
+
+  bool IsTheEmptyMap() const { return data_ == EmptyMap().data_; }
+};
+
+template<typename T>
+void AppendToString(std::string &s, T &&v, bool keys_quoted) {
+    s += "[ ";
+    for (size_t i = 0; i < v.size(); i++) {
+      if (i) s += ", ";
+      v[i].ToString(true, keys_quoted, s);
+    }
+    s += " ]";
+}
+
+class Reference {
+ public:
+  Reference(const uint8_t *data, uint8_t parent_width, uint8_t byte_width,
+            Type type)
+      : data_(data),
+        parent_width_(parent_width),
+        byte_width_(byte_width),
+        type_(type) {}
+
+  Reference(const uint8_t *data, uint8_t parent_width, uint8_t packed_type)
+      : data_(data), parent_width_(parent_width) {
+    byte_width_ = 1U << static_cast<BitWidth>(packed_type & 3);
+    type_ = static_cast<Type>(packed_type >> 2);
+  }
+
+  Type GetType() const { return type_; }
+
+  bool IsNull() const { return type_ == FBT_NULL; }
+  bool IsBool() const { return type_ == FBT_BOOL; }
+  bool IsInt() const { return type_ == FBT_INT || type_ == FBT_INDIRECT_INT; }
+  bool IsUInt() const {
+    return type_ == FBT_UINT || type_ == FBT_INDIRECT_UINT;
+  }
+  bool IsIntOrUint() const { return IsInt() || IsUInt(); }
+  bool IsFloat() const {
+    return type_ == FBT_FLOAT || type_ == FBT_INDIRECT_FLOAT;
+  }
+  bool IsNumeric() const { return IsIntOrUint() || IsFloat(); }
+  bool IsString() const { return type_ == FBT_STRING; }
+  bool IsKey() const { return type_ == FBT_KEY; }
+  bool IsVector() const { return type_ == FBT_VECTOR || type_ == FBT_MAP; }
+  bool IsTypedVector() const { return flexbuffers::IsTypedVector(type_); }
+  bool IsFixedTypedVector() const { return flexbuffers::IsFixedTypedVector(type_); }
+  bool IsAnyVector() const { return (IsTypedVector() || IsFixedTypedVector() || IsVector());}
+  bool IsMap() const { return type_ == FBT_MAP; }
+  bool IsBlob() const { return type_ == FBT_BLOB; }
+
+  bool AsBool() const {
+    return (type_ == FBT_BOOL ? ReadUInt64(data_, parent_width_)
+                               : AsUInt64()) != 0;
+  }
+
+  // Reads any type as a int64_t. Never fails, does most sensible conversion.
+  // Truncates floats, strings are attempted to be parsed for a number,
+  // vectors/maps return their size. Returns 0 if all else fails.
+  int64_t AsInt64() const {
+    if (type_ == FBT_INT) {
+      // A fast path for the common case.
+      return ReadInt64(data_, parent_width_);
+    } else
+      switch (type_) {
+        case FBT_INDIRECT_INT: return ReadInt64(Indirect(), byte_width_);
+        case FBT_UINT: return ReadUInt64(data_, parent_width_);
+        case FBT_INDIRECT_UINT: return ReadUInt64(Indirect(), byte_width_);
+        case FBT_FLOAT:
+          return static_cast<int64_t>(ReadDouble(data_, parent_width_));
+        case FBT_INDIRECT_FLOAT:
+          return static_cast<int64_t>(ReadDouble(Indirect(), byte_width_));
+        case FBT_NULL: return 0;
+        case FBT_STRING: return flatbuffers::StringToInt(AsString().c_str());
+        case FBT_VECTOR: return static_cast<int64_t>(AsVector().size());
+        case FBT_BOOL: return ReadInt64(data_, parent_width_);
+        default:
+          // Convert other things to int.
+          return 0;
+      }
+  }
+
+  // TODO: could specialize these to not use AsInt64() if that saves
+  // extension ops in generated code, and use a faster op than ReadInt64.
+  int32_t AsInt32() const { return static_cast<int32_t>(AsInt64()); }
+  int16_t AsInt16() const { return static_cast<int16_t>(AsInt64()); }
+  int8_t AsInt8() const { return static_cast<int8_t>(AsInt64()); }
+
+  uint64_t AsUInt64() const {
+    if (type_ == FBT_UINT) {
+      // A fast path for the common case.
+      return ReadUInt64(data_, parent_width_);
+    } else
+      switch (type_) {
+        case FBT_INDIRECT_UINT: return ReadUInt64(Indirect(), byte_width_);
+        case FBT_INT: return ReadInt64(data_, parent_width_);
+        case FBT_INDIRECT_INT: return ReadInt64(Indirect(), byte_width_);
+        case FBT_FLOAT:
+          return static_cast<uint64_t>(ReadDouble(data_, parent_width_));
+        case FBT_INDIRECT_FLOAT:
+          return static_cast<uint64_t>(ReadDouble(Indirect(), byte_width_));
+        case FBT_NULL: return 0;
+        case FBT_STRING: return flatbuffers::StringToUInt(AsString().c_str());
+        case FBT_VECTOR: return static_cast<uint64_t>(AsVector().size());
+        case FBT_BOOL: return ReadUInt64(data_, parent_width_);
+        default:
+          // Convert other things to uint.
+          return 0;
+      }
+  }
+
+  uint32_t AsUInt32() const { return static_cast<uint32_t>(AsUInt64()); }
+  uint16_t AsUInt16() const { return static_cast<uint16_t>(AsUInt64()); }
+  uint8_t AsUInt8() const { return static_cast<uint8_t>(AsUInt64()); }
+
+  double AsDouble() const {
+    if (type_ == FBT_FLOAT) {
+      // A fast path for the common case.
+      return ReadDouble(data_, parent_width_);
+    } else
+      switch (type_) {
+        case FBT_INDIRECT_FLOAT: return ReadDouble(Indirect(), byte_width_);
+        case FBT_INT:
+          return static_cast<double>(ReadInt64(data_, parent_width_));
+        case FBT_UINT:
+          return static_cast<double>(ReadUInt64(data_, parent_width_));
+        case FBT_INDIRECT_INT:
+          return static_cast<double>(ReadInt64(Indirect(), byte_width_));
+        case FBT_INDIRECT_UINT:
+          return static_cast<double>(ReadUInt64(Indirect(), byte_width_));
+        case FBT_NULL: return 0.0;
+        case FBT_STRING: return strtod(AsString().c_str(), nullptr);
+        case FBT_VECTOR: return static_cast<double>(AsVector().size());
+        case FBT_BOOL:
+          return static_cast<double>(ReadUInt64(data_, parent_width_));
+        default:
+          // Convert strings and other things to float.
+          return 0;
+      }
+  }
+
+  float AsFloat() const { return static_cast<float>(AsDouble()); }
+
+  const char *AsKey() const {
+    if (type_ == FBT_KEY) {
+      return reinterpret_cast<const char *>(Indirect());
+    } else {
+      return "";
+    }
+  }
+
+  // This function returns the empty string if you try to read a not-string.
+  String AsString() const {
+    if (type_ == FBT_STRING) {
+      return String(Indirect(), byte_width_);
+    } else {
+      return String::EmptyString();
+    }
+  }
+
+  // Unlike AsString(), this will convert any type to a std::string.
+  std::string ToString() const {
+    std::string s;
+    ToString(false, false, s);
+    return s;
+  }
+
+  // Convert any type to a JSON-like string. strings_quoted determines if
+  // string values at the top level receive "" quotes (inside other values
+  // they always do). keys_quoted determines if keys are quoted, at any level.
+  // TODO(wvo): add further options to have indentation/newlines.
+  void ToString(bool strings_quoted, bool keys_quoted, std::string &s) const {
+    if (type_ == FBT_STRING) {
+      String str(Indirect(), byte_width_);
+      if (strings_quoted) {
+        flatbuffers::EscapeString(str.c_str(), str.length(), &s, true, false);
+      } else {
+        s.append(str.c_str(), str.length());
+      }
+    } else if (IsKey()) {
+      auto str = AsKey();
+      if (keys_quoted) {
+        flatbuffers::EscapeString(str, strlen(str), &s, true, false);
+      } else {
+        s += str;
+      }
+    } else if (IsInt()) {
+      s += flatbuffers::NumToString(AsInt64());
+    } else if (IsUInt()) {
+      s += flatbuffers::NumToString(AsUInt64());
+    } else if (IsFloat()) {
+      s += flatbuffers::NumToString(AsDouble());
+    } else if (IsNull()) {
+      s += "null";
+    } else if (IsBool()) {
+      s += AsBool() ? "true" : "false";
+    } else if (IsMap()) {
+      s += "{ ";
+      auto m = AsMap();
+      auto keys = m.Keys();
+      auto vals = m.Values();
+      for (size_t i = 0; i < keys.size(); i++) {
+        keys[i].ToString(true, keys_quoted, s);
+        s += ": ";
+        vals[i].ToString(true, keys_quoted, s);
+        if (i < keys.size() - 1) s += ", ";
+      }
+      s += " }";
+    } else if (IsVector()) {
+      AppendToString<Vector>(s, AsVector(), keys_quoted);
+    } else if (IsTypedVector()) {
+      AppendToString<TypedVector>(s, AsTypedVector(), keys_quoted);
+    } else if (IsFixedTypedVector()) {
+      AppendToString<FixedTypedVector>(s, AsFixedTypedVector(), keys_quoted);
+    } else if (IsBlob()) {
+      auto blob = AsBlob();
+      flatbuffers::EscapeString(reinterpret_cast<const char*>(blob.data()), blob.size(), &s, true, false);
+    } else {
+      s += "(?)";
+    }
+  }
+
+  // This function returns the empty blob if you try to read a not-blob.
+  // Strings can be viewed as blobs too.
+  Blob AsBlob() const {
+    if (type_ == FBT_BLOB || type_ == FBT_STRING) {
+      return Blob(Indirect(), byte_width_);
+    } else {
+      return Blob::EmptyBlob();
+    }
+  }
+
+  // This function returns the empty vector if you try to read a not-vector.
+  // Maps can be viewed as vectors too.
+  Vector AsVector() const {
+    if (type_ == FBT_VECTOR || type_ == FBT_MAP) {
+      return Vector(Indirect(), byte_width_);
+    } else {
+      return Vector::EmptyVector();
+    }
+  }
+
+  TypedVector AsTypedVector() const {
+    if (IsTypedVector()) {
+      return TypedVector(Indirect(), byte_width_,
+                         ToTypedVectorElementType(type_));
+    } else {
+      return TypedVector::EmptyTypedVector();
+    }
+  }
+
+  FixedTypedVector AsFixedTypedVector() const {
+    if (IsFixedTypedVector()) {
+      uint8_t len = 0;
+      auto vtype = ToFixedTypedVectorElementType(type_, &len);
+      return FixedTypedVector(Indirect(), byte_width_, vtype, len);
+    } else {
+      return FixedTypedVector::EmptyFixedTypedVector();
+    }
+  }
+
+  Map AsMap() const {
+    if (type_ == FBT_MAP) {
+      return Map(Indirect(), byte_width_);
+    } else {
+      return Map::EmptyMap();
+    }
+  }
+
+  template<typename T> T As() const;
+
+  // Experimental: Mutation functions.
+  // These allow scalars in an already created buffer to be updated in-place.
+  // Since by default scalars are stored in the smallest possible space,
+  // the new value may not fit, in which case these functions return false.
+  // To avoid this, you can construct the values you intend to mutate using
+  // Builder::ForceMinimumBitWidth.
+  bool MutateInt(int64_t i) {
+    if (type_ == FBT_INT) {
+      return Mutate(data_, i, parent_width_, WidthI(i));
+    } else if (type_ == FBT_INDIRECT_INT) {
+      return Mutate(Indirect(), i, byte_width_, WidthI(i));
+    } else if (type_ == FBT_UINT) {
+      auto u = static_cast<uint64_t>(i);
+      return Mutate(data_, u, parent_width_, WidthU(u));
+    } else if (type_ == FBT_INDIRECT_UINT) {
+      auto u = static_cast<uint64_t>(i);
+      return Mutate(Indirect(), u, byte_width_, WidthU(u));
+    } else {
+      return false;
+    }
+  }
+
+  bool MutateBool(bool b) {
+    return type_ == FBT_BOOL && Mutate(data_, b, parent_width_, BIT_WIDTH_8);
+  }
+
+  bool MutateUInt(uint64_t u) {
+    if (type_ == FBT_UINT) {
+      return Mutate(data_, u, parent_width_, WidthU(u));
+    } else if (type_ == FBT_INDIRECT_UINT) {
+      return Mutate(Indirect(), u, byte_width_, WidthU(u));
+    } else if (type_ == FBT_INT) {
+      auto i = static_cast<int64_t>(u);
+      return Mutate(data_, i, parent_width_, WidthI(i));
+    } else if (type_ == FBT_INDIRECT_INT) {
+      auto i = static_cast<int64_t>(u);
+      return Mutate(Indirect(), i, byte_width_, WidthI(i));
+    } else {
+      return false;
+    }
+  }
+
+  bool MutateFloat(float f) {
+    if (type_ == FBT_FLOAT) {
+      return MutateF(data_, f, parent_width_, BIT_WIDTH_32);
+    } else if (type_ == FBT_INDIRECT_FLOAT) {
+      return MutateF(Indirect(), f, byte_width_, BIT_WIDTH_32);
+    } else {
+      return false;
+    }
+  }
+
+  bool MutateFloat(double d) {
+    if (type_ == FBT_FLOAT) {
+      return MutateF(data_, d, parent_width_, WidthF(d));
+    } else if (type_ == FBT_INDIRECT_FLOAT) {
+      return MutateF(Indirect(), d, byte_width_, WidthF(d));
+    } else {
+      return false;
+    }
+  }
+
+  bool MutateString(const char *str, size_t len) {
+    auto s = AsString();
+    if (s.IsTheEmptyString()) return false;
+    // This is very strict, could allow shorter strings, but that creates
+    // garbage.
+    if (s.length() != len) return false;
+    memcpy(const_cast<char *>(s.c_str()), str, len);
+    return true;
+  }
+  bool MutateString(const char *str) { return MutateString(str, strlen(str)); }
+  bool MutateString(const std::string &str) {
+    return MutateString(str.data(), str.length());
+  }
+
+ private:
+  const uint8_t *Indirect() const {
+    return flexbuffers::Indirect(data_, parent_width_);
+  }
+
+  template<typename T>
+  bool Mutate(const uint8_t *dest, T t, size_t byte_width,
+              BitWidth value_width) {
+    auto fits = static_cast<size_t>(static_cast<size_t>(1U) << value_width) <=
+                byte_width;
+    if (fits) {
+      t = flatbuffers::EndianScalar(t);
+      memcpy(const_cast<uint8_t *>(dest), &t, byte_width);
+    }
+    return fits;
+  }
+
+  template<typename T>
+  bool MutateF(const uint8_t *dest, T t, size_t byte_width,
+               BitWidth value_width) {
+    if (byte_width == sizeof(double))
+      return Mutate(dest, static_cast<double>(t), byte_width, value_width);
+    if (byte_width == sizeof(float))
+      return Mutate(dest, static_cast<float>(t), byte_width, value_width);
+    FLATBUFFERS_ASSERT(false);
+    return false;
+  }
+
+  const uint8_t *data_;
+  uint8_t parent_width_;
+  uint8_t byte_width_;
+  Type type_;
+};
+
+// Template specialization for As().
+template<> inline bool Reference::As<bool>() const { return AsBool(); }
+
+template<> inline int8_t Reference::As<int8_t>() const { return AsInt8(); }
+template<> inline int16_t Reference::As<int16_t>() const { return AsInt16(); }
+template<> inline int32_t Reference::As<int32_t>() const { return AsInt32(); }
+template<> inline int64_t Reference::As<int64_t>() const { return AsInt64(); }
+
+template<> inline uint8_t Reference::As<uint8_t>() const { return AsUInt8(); }
+template<> inline uint16_t Reference::As<uint16_t>() const { return AsUInt16(); }
+template<> inline uint32_t Reference::As<uint32_t>() const { return AsUInt32(); }
+template<> inline uint64_t Reference::As<uint64_t>() const { return AsUInt64(); }
+
+template<> inline double Reference::As<double>() const { return AsDouble(); }
+template<> inline float Reference::As<float>() const { return AsFloat(); }
+
+template<> inline String Reference::As<String>() const { return AsString(); }
+template<> inline std::string Reference::As<std::string>() const {
+  return AsString().str();
+}
+
+template<> inline Blob Reference::As<Blob>() const { return AsBlob(); }
+template<> inline Vector Reference::As<Vector>() const { return AsVector(); }
+template<> inline TypedVector Reference::As<TypedVector>() const {
+  return AsTypedVector();
+}
+template<> inline FixedTypedVector Reference::As<FixedTypedVector>() const {
+  return AsFixedTypedVector();
+}
+template<> inline Map Reference::As<Map>() const { return AsMap(); }
+
+inline uint8_t PackedType(BitWidth bit_width, Type type) {
+  return static_cast<uint8_t>(bit_width | (type << 2));
+}
+
+inline uint8_t NullPackedType() { return PackedType(BIT_WIDTH_8, FBT_NULL); }
+
+// Vector accessors.
+// Note: if you try to access outside of bounds, you get a Null value back
+// instead. Normally this would be an assert, but since this is "dynamically
+// typed" data, you may not want that (someone sends you a 2d vector and you
+// wanted 3d).
+// The Null converts seamlessly into a default value for any other type.
+// TODO(wvo): Could introduce an #ifdef that makes this into an assert?
+inline Reference Vector::operator[](size_t i) const {
+  auto len = size();
+  if (i >= len) return Reference(nullptr, 1, NullPackedType());
+  auto packed_type = (data_ + len * byte_width_)[i];
+  auto elem = data_ + i * byte_width_;
+  return Reference(elem, byte_width_, packed_type);
+}
+
+inline Reference TypedVector::operator[](size_t i) const {
+  auto len = size();
+  if (i >= len) return Reference(nullptr, 1, NullPackedType());
+  auto elem = data_ + i * byte_width_;
+  return Reference(elem, byte_width_, 1, type_);
+}
+
+inline Reference FixedTypedVector::operator[](size_t i) const {
+  if (i >= len_) return Reference(nullptr, 1, NullPackedType());
+  auto elem = data_ + i * byte_width_;
+  return Reference(elem, byte_width_, 1, type_);
+}
+
+template<typename T> int KeyCompare(const void *key, const void *elem) {
+  auto str_elem = reinterpret_cast<const char *>(
+      Indirect<T>(reinterpret_cast<const uint8_t *>(elem)));
+  auto skey = reinterpret_cast<const char *>(key);
+  return strcmp(skey, str_elem);
+}
+
+inline Reference Map::operator[](const char *key) const {
+  auto keys = Keys();
+  // We can't pass keys.byte_width_ to the comparison function, so we have
+  // to pick the right one ahead of time.
+  int (*comp)(const void *, const void *) = nullptr;
+  switch (keys.byte_width_) {
+    case 1: comp = KeyCompare<uint8_t>; break;
+    case 2: comp = KeyCompare<uint16_t>; break;
+    case 4: comp = KeyCompare<uint32_t>; break;
+    case 8: comp = KeyCompare<uint64_t>; break;
+  }
+  auto res = std::bsearch(key, keys.data_, keys.size(), keys.byte_width_, comp);
+  if (!res) return Reference(nullptr, 1, NullPackedType());
+  auto i = (reinterpret_cast<uint8_t *>(res) - keys.data_) / keys.byte_width_;
+  return (*static_cast<const Vector *>(this))[i];
+}
+
+inline Reference Map::operator[](const std::string &key) const {
+  return (*this)[key.c_str()];
+}
+
+inline Reference GetRoot(const uint8_t *buffer, size_t size) {
+  // See Finish() below for the serialization counterpart of this.
+  // The root starts at the end of the buffer, so we parse backwards from there.
+  auto end = buffer + size;
+  auto byte_width = *--end;
+  auto packed_type = *--end;
+  end -= byte_width;  // The root data item.
+  return Reference(end, byte_width, packed_type);
+}
+
+inline Reference GetRoot(const std::vector<uint8_t> &buffer) {
+  return GetRoot(flatbuffers::vector_data(buffer), buffer.size());
+}
+
+// Flags that configure how the Builder behaves.
+// The "Share" flags determine if the Builder automatically tries to pool
+// this type. Pooling can reduce the size of serialized data if there are
+// multiple maps of the same kind, at the expense of slightly slower
+// serialization (the cost of lookups) and more memory use (std::set).
+// By default this is on for keys, but off for strings.
+// Turn keys off if you have e.g. only one map.
+// Turn strings on if you expect many non-unique string values.
+// Additionally, sharing key vectors can save space if you have maps with
+// identical field populations.
+enum BuilderFlag {
+  BUILDER_FLAG_NONE = 0,
+  BUILDER_FLAG_SHARE_KEYS = 1,
+  BUILDER_FLAG_SHARE_STRINGS = 2,
+  BUILDER_FLAG_SHARE_KEYS_AND_STRINGS = 3,
+  BUILDER_FLAG_SHARE_KEY_VECTORS = 4,
+  BUILDER_FLAG_SHARE_ALL = 7,
+};
+
+class Builder FLATBUFFERS_FINAL_CLASS {
+ public:
+  Builder(size_t initial_size = 256,
+          BuilderFlag flags = BUILDER_FLAG_SHARE_KEYS)
+      : buf_(initial_size),
+        finished_(false),
+        flags_(flags),
+        force_min_bit_width_(BIT_WIDTH_8),
+        key_pool(KeyOffsetCompare(buf_)),
+        string_pool(StringOffsetCompare(buf_)) {
+    buf_.clear();
+  }
+
+  /// @brief Get the serialized buffer (after you call `Finish()`).
+  /// @return Returns a vector owned by this class.
+  const std::vector<uint8_t> &GetBuffer() const {
+    Finished();
+    return buf_;
+  }
+
+  // Size of the buffer. Does not include unfinished values.
+  size_t GetSize() const { return buf_.size(); }
+
+  // Reset all state so we can re-use the buffer.
+  void Clear() {
+    buf_.clear();
+    stack_.clear();
+    finished_ = false;
+    // flags_ remains as-is;
+    force_min_bit_width_ = BIT_WIDTH_8;
+    key_pool.clear();
+    string_pool.clear();
+  }
+
+  // All value constructing functions below have two versions: one that
+  // takes a key (for placement inside a map) and one that doesn't (for inside
+  // vectors and elsewhere).
+
+  void Null() { stack_.push_back(Value()); }
+  void Null(const char *key) {
+    Key(key);
+    Null();
+  }
+
+  void Int(int64_t i) { stack_.push_back(Value(i, FBT_INT, WidthI(i))); }
+  void Int(const char *key, int64_t i) {
+    Key(key);
+    Int(i);
+  }
+
+  void UInt(uint64_t u) { stack_.push_back(Value(u, FBT_UINT, WidthU(u))); }
+  void UInt(const char *key, uint64_t u) {
+    Key(key);
+    UInt(u);
+  }
+
+  void Float(float f) { stack_.push_back(Value(f)); }
+  void Float(const char *key, float f) {
+    Key(key);
+    Float(f);
+  }
+
+  void Double(double f) { stack_.push_back(Value(f)); }
+  void Double(const char *key, double d) {
+    Key(key);
+    Double(d);
+  }
+
+  void Bool(bool b) { stack_.push_back(Value(b)); }
+  void Bool(const char *key, bool b) {
+    Key(key);
+    Bool(b);
+  }
+
+  void IndirectInt(int64_t i) { PushIndirect(i, FBT_INDIRECT_INT, WidthI(i)); }
+  void IndirectInt(const char *key, int64_t i) {
+    Key(key);
+    IndirectInt(i);
+  }
+
+  void IndirectUInt(uint64_t u) {
+    PushIndirect(u, FBT_INDIRECT_UINT, WidthU(u));
+  }
+  void IndirectUInt(const char *key, uint64_t u) {
+    Key(key);
+    IndirectUInt(u);
+  }
+
+  void IndirectFloat(float f) {
+    PushIndirect(f, FBT_INDIRECT_FLOAT, BIT_WIDTH_32);
+  }
+  void IndirectFloat(const char *key, float f) {
+    Key(key);
+    IndirectFloat(f);
+  }
+
+  void IndirectDouble(double f) {
+    PushIndirect(f, FBT_INDIRECT_FLOAT, WidthF(f));
+  }
+  void IndirectDouble(const char *key, double d) {
+    Key(key);
+    IndirectDouble(d);
+  }
+
+  size_t Key(const char *str, size_t len) {
+    auto sloc = buf_.size();
+    WriteBytes(str, len + 1);
+    if (flags_ & BUILDER_FLAG_SHARE_KEYS) {
+      auto it = key_pool.find(sloc);
+      if (it != key_pool.end()) {
+        // Already in the buffer. Remove key we just serialized, and use
+        // existing offset instead.
+        buf_.resize(sloc);
+        sloc = *it;
+      } else {
+        key_pool.insert(sloc);
+      }
+    }
+    stack_.push_back(Value(static_cast<uint64_t>(sloc), FBT_KEY, BIT_WIDTH_8));
+    return sloc;
+  }
+
+  size_t Key(const char *str) { return Key(str, strlen(str)); }
+  size_t Key(const std::string &str) { return Key(str.c_str(), str.size()); }
+
+  size_t String(const char *str, size_t len) {
+    auto reset_to = buf_.size();
+    auto sloc = CreateBlob(str, len, 1, FBT_STRING);
+    if (flags_ & BUILDER_FLAG_SHARE_STRINGS) {
+      StringOffset so(sloc, len);
+      auto it = string_pool.find(so);
+      if (it != string_pool.end()) {
+        // Already in the buffer. Remove string we just serialized, and use
+        // existing offset instead.
+        buf_.resize(reset_to);
+        sloc = it->first;
+        stack_.back().u_ = sloc;
+      } else {
+        string_pool.insert(so);
+      }
+    }
+    return sloc;
+  }
+  size_t String(const char *str) { return String(str, strlen(str)); }
+  size_t String(const std::string &str) {
+    return String(str.c_str(), str.size());
+  }
+  void String(const flexbuffers::String &str) {
+    String(str.c_str(), str.length());
+  }
+
+  void String(const char *key, const char *str) {
+    Key(key);
+    String(str);
+  }
+  void String(const char *key, const std::string &str) {
+    Key(key);
+    String(str);
+  }
+  void String(const char *key, const flexbuffers::String &str) {
+    Key(key);
+    String(str);
+  }
+
+  size_t Blob(const void *data, size_t len) {
+    return CreateBlob(data, len, 0, FBT_BLOB);
+  }
+  size_t Blob(const std::vector<uint8_t> &v) {
+    return CreateBlob(flatbuffers::vector_data(v), v.size(), 0, FBT_BLOB);
+  }
+
+  // TODO(wvo): support all the FlexBuffer types (like flexbuffers::String),
+  // e.g. Vector etc. Also in overloaded versions.
+  // Also some FlatBuffers types?
+
+  size_t StartVector() { return stack_.size(); }
+  size_t StartVector(const char *key) {
+    Key(key);
+    return stack_.size();
+  }
+  size_t StartMap() { return stack_.size(); }
+  size_t StartMap(const char *key) {
+    Key(key);
+    return stack_.size();
+  }
+
+  // TODO(wvo): allow this to specify an aligment greater than the natural
+  // alignment.
+  size_t EndVector(size_t start, bool typed, bool fixed) {
+    auto vec = CreateVector(start, stack_.size() - start, 1, typed, fixed);
+    // Remove temp elements and return vector.
+    stack_.resize(start);
+    stack_.push_back(vec);
+    return static_cast<size_t>(vec.u_);
+  }
+
+  size_t EndMap(size_t start) {
+    // We should have interleaved keys and values on the stack.
+    // Make sure it is an even number:
+    auto len = stack_.size() - start;
+    FLATBUFFERS_ASSERT(!(len & 1));
+    len /= 2;
+    // Make sure keys are all strings:
+    for (auto key = start; key < stack_.size(); key += 2) {
+      FLATBUFFERS_ASSERT(stack_[key].type_ == FBT_KEY);
+    }
+    // Now sort values, so later we can do a binary seach lookup.
+    // We want to sort 2 array elements at a time.
+    struct TwoValue {
+      Value key;
+      Value val;
+    };
+    // TODO(wvo): strict aliasing?
+    // TODO(wvo): allow the caller to indicate the data is already sorted
+    // for maximum efficiency? With an assert to check sortedness to make sure
+    // we're not breaking binary search.
+    // Or, we can track if the map is sorted as keys are added which would be
+    // be quite cheap (cheaper than checking it here), so we can skip this
+    // step automatically when appliccable, and encourage people to write in
+    // sorted fashion.
+    // std::sort is typically already a lot faster on sorted data though.
+    auto dict =
+        reinterpret_cast<TwoValue *>(flatbuffers::vector_data(stack_) + start);
+    std::sort(dict, dict + len,
+              [&](const TwoValue &a, const TwoValue &b) -> bool {
+                auto as = reinterpret_cast<const char *>(
+                    flatbuffers::vector_data(buf_) + a.key.u_);
+                auto bs = reinterpret_cast<const char *>(
+                    flatbuffers::vector_data(buf_) + b.key.u_);
+                auto comp = strcmp(as, bs);
+                // If this assertion hits, you've added two keys with the same
+                // value to this map.
+                // TODO: Have to check for pointer equality, as some sort
+                // implementation apparently call this function with the same
+                // element?? Why?
+                FLATBUFFERS_ASSERT(comp || &a == &b);
+                return comp < 0;
+              });
+    // First create a vector out of all keys.
+    // TODO(wvo): if kBuilderFlagShareKeyVectors is true, see if we can share
+    // the first vector.
+    auto keys = CreateVector(start, len, 2, true, false);
+    auto vec = CreateVector(start + 1, len, 2, false, false, &keys);
+    // Remove temp elements and return map.
+    stack_.resize(start);
+    stack_.push_back(vec);
+    return static_cast<size_t>(vec.u_);
+  }
+
+  template<typename F> size_t Vector(F f) {
+    auto start = StartVector();
+    f();
+    return EndVector(start, false, false);
+  }
+  template<typename F, typename T> size_t Vector(F f, T &state) {
+    auto start = StartVector();
+    f(state);
+    return EndVector(start, false, false);
+  }
+  template<typename F> size_t Vector(const char *key, F f) {
+    auto start = StartVector(key);
+    f();
+    return EndVector(start, false, false);
+  }
+  template<typename F, typename T>
+  size_t Vector(const char *key, F f, T &state) {
+    auto start = StartVector(key);
+    f(state);
+    return EndVector(start, false, false);
+  }
+
+  template<typename T> void Vector(const T *elems, size_t len) {
+    if (flatbuffers::is_scalar<T>::value) {
+      // This path should be a lot quicker and use less space.
+      ScalarVector(elems, len, false);
+    } else {
+      auto start = StartVector();
+      for (size_t i = 0; i < len; i++) Add(elems[i]);
+      EndVector(start, false, false);
+    }
+  }
+  template<typename T>
+  void Vector(const char *key, const T *elems, size_t len) {
+    Key(key);
+    Vector(elems, len);
+  }
+  template<typename T> void Vector(const std::vector<T> &vec) {
+    Vector(flatbuffers::vector_data(vec), vec.size());
+  }
+
+  template<typename F> size_t TypedVector(F f) {
+    auto start = StartVector();
+    f();
+    return EndVector(start, true, false);
+  }
+  template<typename F, typename T> size_t TypedVector(F f, T &state) {
+    auto start = StartVector();
+    f(state);
+    return EndVector(start, true, false);
+  }
+  template<typename F> size_t TypedVector(const char *key, F f) {
+    auto start = StartVector(key);
+    f();
+    return EndVector(start, true, false);
+  }
+  template<typename F, typename T>
+  size_t TypedVector(const char *key, F f, T &state) {
+    auto start = StartVector(key);
+    f(state);
+    return EndVector(start, true, false);
+  }
+
+  template<typename T> size_t FixedTypedVector(const T *elems, size_t len) {
+    // We only support a few fixed vector lengths. Anything bigger use a
+    // regular typed vector.
+    FLATBUFFERS_ASSERT(len >= 2 && len <= 4);
+    // And only scalar values.
+    static_assert(flatbuffers::is_scalar<T>::value, "Unrelated types");
+    return ScalarVector(elems, len, true);
+  }
+
+  template<typename T>
+  size_t FixedTypedVector(const char *key, const T *elems, size_t len) {
+    Key(key);
+    return FixedTypedVector(elems, len);
+  }
+
+  template<typename F> size_t Map(F f) {
+    auto start = StartMap();
+    f();
+    return EndMap(start);
+  }
+  template<typename F, typename T> size_t Map(F f, T &state) {
+    auto start = StartMap();
+    f(state);
+    return EndMap(start);
+  }
+  template<typename F> size_t Map(const char *key, F f) {
+    auto start = StartMap(key);
+    f();
+    return EndMap(start);
+  }
+  template<typename F, typename T> size_t Map(const char *key, F f, T &state) {
+    auto start = StartMap(key);
+    f(state);
+    return EndMap(start);
+  }
+  template<typename T> void Map(const std::map<std::string, T> &map) {
+    auto start = StartMap();
+    for (auto it = map.begin(); it != map.end(); ++it)
+      Add(it->first.c_str(), it->second);
+    EndMap(start);
+  }
+
+  // Overloaded Add that tries to call the correct function above.
+  void Add(int8_t i) { Int(i); }
+  void Add(int16_t i) { Int(i); }
+  void Add(int32_t i) { Int(i); }
+  void Add(int64_t i) { Int(i); }
+  void Add(uint8_t u) { UInt(u); }
+  void Add(uint16_t u) { UInt(u); }
+  void Add(uint32_t u) { UInt(u); }
+  void Add(uint64_t u) { UInt(u); }
+  void Add(float f) { Float(f); }
+  void Add(double d) { Double(d); }
+  void Add(bool b) { Bool(b); }
+  void Add(const char *str) { String(str); }
+  void Add(const std::string &str) { String(str); }
+  void Add(const flexbuffers::String &str) { String(str); }
+
+  template<typename T> void Add(const std::vector<T> &vec) { Vector(vec); }
+
+  template<typename T> void Add(const char *key, const T &t) {
+    Key(key);
+    Add(t);
+  }
+
+  template<typename T> void Add(const std::map<std::string, T> &map) {
+    Map(map);
+  }
+
+  template<typename T> void operator+=(const T &t) { Add(t); }
+
+  // This function is useful in combination with the Mutate* functions above.
+  // It forces elements of vectors and maps to have a minimum size, such that
+  // they can later be updated without failing.
+  // Call with no arguments to reset.
+  void ForceMinimumBitWidth(BitWidth bw = BIT_WIDTH_8) {
+    force_min_bit_width_ = bw;
+  }
+
+  void Finish() {
+    // If you hit this assert, you likely have objects that were never included
+    // in a parent. You need to have exactly one root to finish a buffer.
+    // Check your Start/End calls are matched, and all objects are inside
+    // some other object.
+    FLATBUFFERS_ASSERT(stack_.size() == 1);
+
+    // Write root value.
+    auto byte_width = Align(stack_[0].ElemWidth(buf_.size(), 0));
+    WriteAny(stack_[0], byte_width);
+    // Write root type.
+    Write(stack_[0].StoredPackedType(), 1);
+    // Write root size. Normally determined by parent, but root has no parent :)
+    Write(byte_width, 1);
+
+    finished_ = true;
+  }
+
+ private:
+  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
+    // Builder::Finish with your root object.
+    FLATBUFFERS_ASSERT(finished_);
+  }
+
+  // Align to prepare for writing a scalar with a certain size.
+  uint8_t Align(BitWidth alignment) {
+    auto byte_width = 1U << alignment;
+    buf_.insert(buf_.end(), flatbuffers::PaddingBytes(buf_.size(), byte_width),
+                0);
+    return static_cast<uint8_t>(byte_width);
+  }
+
+  void WriteBytes(const void *val, size_t size) {
+    buf_.insert(buf_.end(), reinterpret_cast<const uint8_t *>(val),
+                reinterpret_cast<const uint8_t *>(val) + size);
+  }
+
+  template<typename T> void Write(T val, size_t byte_width) {
+    FLATBUFFERS_ASSERT(sizeof(T) >= byte_width);
+    val = flatbuffers::EndianScalar(val);
+    WriteBytes(&val, byte_width);
+  }
+
+  void WriteDouble(double f, uint8_t byte_width) {
+    switch (byte_width) {
+      case 8: Write(f, byte_width); break;
+      case 4: Write(static_cast<float>(f), byte_width); break;
+      // case 2: Write(static_cast<half>(f), byte_width); break;
+      // case 1: Write(static_cast<quarter>(f), byte_width); break;
+      default: FLATBUFFERS_ASSERT(0);
+    }
+  }
+
+  void WriteOffset(uint64_t o, uint8_t byte_width) {
+    auto reloff = buf_.size() - o;
+    FLATBUFFERS_ASSERT(byte_width == 8 || reloff < 1ULL << (byte_width * 8));
+    Write(reloff, byte_width);
+  }
+
+  template<typename T> void PushIndirect(T val, Type type, BitWidth bit_width) {
+    auto byte_width = Align(bit_width);
+    auto iloc = buf_.size();
+    Write(val, byte_width);
+    stack_.push_back(Value(static_cast<uint64_t>(iloc), type, bit_width));
+  }
+
+  static BitWidth WidthB(size_t byte_width) {
+    switch (byte_width) {
+      case 1: return BIT_WIDTH_8;
+      case 2: return BIT_WIDTH_16;
+      case 4: return BIT_WIDTH_32;
+      case 8: return BIT_WIDTH_64;
+      default: FLATBUFFERS_ASSERT(false); return BIT_WIDTH_64;
+    }
+  }
+
+  template<typename T> static Type GetScalarType() {
+    static_assert(flatbuffers::is_scalar<T>::value, "Unrelated types");
+    return flatbuffers::is_floating_point<T>::value
+               ? FBT_FLOAT
+               : flatbuffers::is_same<T, bool>::value
+                     ? FBT_BOOL
+                     : (flatbuffers::is_unsigned<T>::value ? FBT_UINT
+                                                           : FBT_INT);
+  }
+
+  struct Value {
+    union {
+      int64_t i_;
+      uint64_t u_;
+      double f_;
+    };
+
+    Type type_;
+
+    // For scalars: of itself, for vector: of its elements, for string: length.
+    BitWidth min_bit_width_;
+
+    Value() : i_(0), type_(FBT_NULL), min_bit_width_(BIT_WIDTH_8) {}
+
+    Value(bool b)
+        : u_(static_cast<uint64_t>(b)),
+          type_(FBT_BOOL),
+          min_bit_width_(BIT_WIDTH_8) {}
+
+    Value(int64_t i, Type t, BitWidth bw)
+        : i_(i), type_(t), min_bit_width_(bw) {}
+    Value(uint64_t u, Type t, BitWidth bw)
+        : u_(u), type_(t), min_bit_width_(bw) {}
+
+    Value(float f) : f_(f), type_(FBT_FLOAT), min_bit_width_(BIT_WIDTH_32) {}
+    Value(double f) : f_(f), type_(FBT_FLOAT), min_bit_width_(WidthF(f)) {}
+
+    uint8_t StoredPackedType(BitWidth parent_bit_width_ = BIT_WIDTH_8) const {
+      return PackedType(StoredWidth(parent_bit_width_), type_);
+    }
+
+    BitWidth ElemWidth(size_t buf_size, size_t elem_index) const {
+      if (IsInline(type_)) {
+        return min_bit_width_;
+      } else {
+        // We have an absolute offset, but want to store a relative offset
+        // elem_index elements beyond the current buffer end. Since whether
+        // the relative offset fits in a certain byte_width depends on
+        // the size of the elements before it (and their alignment), we have
+        // to test for each size in turn.
+        for (size_t byte_width = 1;
+             byte_width <= sizeof(flatbuffers::largest_scalar_t);
+             byte_width *= 2) {
+          // Where are we going to write this offset?
+          auto offset_loc = buf_size +
+                            flatbuffers::PaddingBytes(buf_size, byte_width) +
+                            elem_index * byte_width;
+          // Compute relative offset.
+          auto offset = offset_loc - u_;
+          // Does it fit?
+          auto bit_width = WidthU(offset);
+          if (static_cast<size_t>(static_cast<size_t>(1U) << bit_width) ==
+              byte_width)
+            return bit_width;
+        }
+        FLATBUFFERS_ASSERT(false);  // Must match one of the sizes above.
+        return BIT_WIDTH_64;
+      }
+    }
+
+    BitWidth StoredWidth(BitWidth parent_bit_width_ = BIT_WIDTH_8) const {
+      if (IsInline(type_)) {
+        return (std::max)(min_bit_width_, parent_bit_width_);
+      } else {
+        return min_bit_width_;
+      }
+    }
+  };
+
+  void WriteAny(const Value &val, uint8_t byte_width) {
+    switch (val.type_) {
+      case FBT_NULL:
+      case FBT_INT: Write(val.i_, byte_width); break;
+      case FBT_BOOL:
+      case FBT_UINT: Write(val.u_, byte_width); break;
+      case FBT_FLOAT: WriteDouble(val.f_, byte_width); break;
+      default: WriteOffset(val.u_, byte_width); break;
+    }
+  }
+
+  size_t CreateBlob(const void *data, size_t len, size_t trailing, Type type) {
+    auto bit_width = WidthU(len);
+    auto byte_width = Align(bit_width);
+    Write<uint64_t>(len, byte_width);
+    auto sloc = buf_.size();
+    WriteBytes(data, len + trailing);
+    stack_.push_back(Value(static_cast<uint64_t>(sloc), type, bit_width));
+    return sloc;
+  }
+
+  template<typename T>
+  size_t ScalarVector(const T *elems, size_t len, bool fixed) {
+    auto vector_type = GetScalarType<T>();
+    auto byte_width = sizeof(T);
+    auto bit_width = WidthB(byte_width);
+    // If you get this assert, you're trying to write a vector with a size
+    // field that is bigger than the scalars you're trying to write (e.g. a
+    // byte vector > 255 elements). For such types, write a "blob" instead.
+    // TODO: instead of asserting, could write vector with larger elements
+    // instead, though that would be wasteful.
+    FLATBUFFERS_ASSERT(WidthU(len) <= bit_width);
+    if (!fixed) Write<uint64_t>(len, byte_width);
+    auto vloc = buf_.size();
+    for (size_t i = 0; i < len; i++) Write(elems[i], byte_width);
+    stack_.push_back(Value(static_cast<uint64_t>(vloc),
+                           ToTypedVector(vector_type, fixed ? len : 0),
+                           bit_width));
+    return vloc;
+  }
+
+  Value CreateVector(size_t start, size_t vec_len, size_t step, bool typed,
+                     bool fixed, const Value *keys = nullptr) {
+    FLATBUFFERS_ASSERT(!fixed || typed); // typed=false, fixed=true combination is not supported.
+    // Figure out smallest bit width we can store this vector with.
+    auto bit_width = (std::max)(force_min_bit_width_, WidthU(vec_len));
+    auto prefix_elems = 1;
+    if (keys) {
+      // If this vector is part of a map, we will pre-fix an offset to the keys
+      // to this vector.
+      bit_width = (std::max)(bit_width, keys->ElemWidth(buf_.size(), 0));
+      prefix_elems += 2;
+    }
+    Type vector_type = FBT_KEY;
+    // Check bit widths and types for all elements.
+    for (size_t i = start; i < stack_.size(); i += step) {
+      auto elem_width = stack_[i].ElemWidth(buf_.size(), i + prefix_elems);
+      bit_width = (std::max)(bit_width, elem_width);
+      if (typed) {
+        if (i == start) {
+          vector_type = stack_[i].type_;
+        } else {
+          // If you get this assert, you are writing a typed vector with
+          // elements that are not all the same type.
+          FLATBUFFERS_ASSERT(vector_type == stack_[i].type_);
+        }
+      }
+    }
+    // If you get this assert, your fixed types are not one of:
+    // Int / UInt / Float / Key.
+    FLATBUFFERS_ASSERT(!fixed || IsTypedVectorElementType(vector_type));
+    auto byte_width = Align(bit_width);
+    // Write vector. First the keys width/offset if available, and size.
+    if (keys) {
+      WriteOffset(keys->u_, byte_width);
+      Write<uint64_t>(1ULL << keys->min_bit_width_, byte_width);
+    }
+    if (!fixed) Write<uint64_t>(vec_len, byte_width);
+    // Then the actual data.
+    auto vloc = buf_.size();
+    for (size_t i = start; i < stack_.size(); i += step) {
+      WriteAny(stack_[i], byte_width);
+    }
+    // Then the types.
+    if (!typed) {
+      for (size_t i = start; i < stack_.size(); i += step) {
+        buf_.push_back(stack_[i].StoredPackedType(bit_width));
+      }
+    }
+    return Value(static_cast<uint64_t>(vloc),
+                 keys ? FBT_MAP
+                      : (typed ? ToTypedVector(vector_type, fixed ? vec_len : 0)
+                               : FBT_VECTOR),
+                 bit_width);
+  }
+
+  // You shouldn't really be copying instances of this class.
+  Builder(const Builder &);
+  Builder &operator=(const Builder &);
+
+  std::vector<uint8_t> buf_;
+  std::vector<Value> stack_;
+
+  bool finished_;
+
+  BuilderFlag flags_;
+
+  BitWidth force_min_bit_width_;
+
+  struct KeyOffsetCompare {
+    explicit KeyOffsetCompare(const std::vector<uint8_t> &buf) : buf_(&buf) {}
+    bool operator()(size_t a, size_t b) const {
+      auto stra =
+          reinterpret_cast<const char *>(flatbuffers::vector_data(*buf_) + a);
+      auto strb =
+          reinterpret_cast<const char *>(flatbuffers::vector_data(*buf_) + b);
+      return strcmp(stra, strb) < 0;
+    }
+    const std::vector<uint8_t> *buf_;
+  };
+
+  typedef std::pair<size_t, size_t> StringOffset;
+  struct StringOffsetCompare {
+    explicit StringOffsetCompare(const std::vector<uint8_t> &buf) : buf_(&buf) {}
+    bool operator()(const StringOffset &a, const StringOffset &b) const {
+      auto stra = reinterpret_cast<const char *>(
+          flatbuffers::vector_data(*buf_) + a.first);
+      auto strb = reinterpret_cast<const char *>(
+          flatbuffers::vector_data(*buf_) + b.first);
+      return strncmp(stra, strb, (std::min)(a.second, b.second) + 1) < 0;
+    }
+    const std::vector<uint8_t> *buf_;
+  };
+
+  typedef std::set<size_t, KeyOffsetCompare> KeyOffsetMap;
+  typedef std::set<StringOffset, StringOffsetCompare> StringOffsetMap;
+
+  KeyOffsetMap key_pool;
+  StringOffsetMap string_pool;
+};
+
+}  // namespace flexbuffers
+
+#  if defined(_MSC_VER)
+#    pragma warning(pop)
+#  endif
+
+#endif  // FLATBUFFERS_FLEXBUFFERS_H_