[C++] Fix compile failure on Object API union construction for struct member (#6923)

* Add dedicated traits to Object API version of unions.

* Add suppression for unused parameters on unions of structs.

27 files changed, 1954 insertions, 11 deletions

diff --git a/tests/FlatBuffers.Test.Swift/Tests/FlatBuffers.Test.SwiftTests/union_vector_generated.swift b/tests/FlatBuffers.Test.Swift/Tests/FlatBuffers.Test.SwiftTests/union_vector_generated.swift
index 13abd04c..59ed0053 100644
--- a/tests/FlatBuffers.Test.Swift/Tests/FlatBuffers.Test.SwiftTests/union_vector_generated.swift
+++ b/tests/FlatBuffers.Test.Swift/Tests/FlatBuffers.Test.SwiftTests/union_vector_generated.swift
@@ -71,6 +71,53 @@ public struct CharacterUnion {
     }
   }
 }
+public enum Gadget: UInt8, UnionEnum {
+  public typealias T = UInt8
+
+  public init?(value: T) {
+    self.init(rawValue: value)
+  }
+
+  public static var byteSize: Int { return MemoryLayout<UInt8>.size }
+  public var value: UInt8 { return self.rawValue }
+  case none_ = 0
+  case fallingtub = 1
+  case handfan = 2
+
+  public static var max: Gadget { return .handfan }
+  public static var min: Gadget { return .none_ }
+}
+
+extension Gadget: Encodable {
+  public func encode(to encoder: Encoder) throws {
+    var container = encoder.singleValueContainer()
+    switch self {
+    case .none_: try container.encode("NONE")
+    case .fallingtub: try container.encode("FallingTub")
+    case .handfan: try container.encode("HandFan")
+    }
+  }
+}
+
+public struct GadgetUnion {
+  public var type: Gadget
+  public var value: NativeObject?
+  public init(_ v: NativeObject?, type: Gadget) {
+    self.type = type
+    self.value = v
+  }
+  public func pack(builder: inout FlatBufferBuilder) -> Offset {
+    switch type {
+    case .fallingtub:
+      var __obj = value as? FallingTub
+      return FallingTub_Mutable.pack(&builder, obj: &__obj)
+    case .handfan:
+      var __obj = value as? HandFanT
+      return HandFan.pack(&builder, obj: &__obj)
+    default: return Offset()
+    }
+  }
+}
 public struct Rapunzel: NativeStruct, Verifiable, FlatbuffersInitializable, NativeObject {
 
   static func validateVersion() { FlatBuffersVersion_2_0_0() }
@@ -207,6 +254,74 @@ public struct BookReader_Mutable: FlatBufferObject {
   }
 }
 
+public struct FallingTub: NativeStruct, Verifiable, FlatbuffersInitializable, NativeObject {
+
+  static func validateVersion() { FlatBuffersVersion_2_0_0() }
+
+  private var _weight: Int32
+
+  public init(_ bb: ByteBuffer, o: Int32) {
+    let _accessor = Struct(bb: bb, position: o)
+    _weight = _accessor.readBuffer(of: Int32.self, at: 0)
+  }
+
+  public init(weight: Int32) {
+    _weight = weight
+  }
+
+  public init() {
+    _weight = 0
+  }
+
+  public init(_ _t: inout FallingTub_Mutable) {
+    _weight = _t.weight
+  }
+
+  public var weight: Int32 { _weight }
+
+  public static func verify<T>(_ verifier: inout Verifier, at position: Int, of type: T.Type) throws where T: Verifiable {
+    try verifier.inBuffer(position: position, of: FallingTub.self)
+  }
+}
+
+extension FallingTub: Encodable {
+
+  enum CodingKeys: String, CodingKey {
+    case weight = "weight"
+  }
+  public func encode(to encoder: Encoder) throws {
+    var container = encoder.container(keyedBy: CodingKeys.self)
+    if weight != 0 {
+      try container.encodeIfPresent(weight, forKey: .weight)
+    }
+  }
+}
+
+public struct FallingTub_Mutable: FlatBufferObject {
+
+  static func validateVersion() { FlatBuffersVersion_2_0_0() }
+  public var __buffer: ByteBuffer! { return _accessor.bb }
+  private var _accessor: Struct
+
+  public init(_ bb: ByteBuffer, o: Int32) { _accessor = Struct(bb: bb, position: o) }
+
+  public var weight: Int32 { return _accessor.readBuffer(of: Int32.self, at: 0) }
+  @discardableResult public func mutate(weight: Int32) -> Bool { return _accessor.mutate(weight, index: 0) }
+  
+
+  public mutating func unpack() -> FallingTub {
+    return FallingTub(&self)
+  }
+  public static func pack(_ builder: inout FlatBufferBuilder, obj: inout FallingTub?) -> Offset {
+    guard var obj = obj else { return Offset() }
+    return pack(&builder, obj: &obj)
+  }
+
+  public static func pack(_ builder: inout FlatBufferBuilder, obj: inout FallingTub) -> Offset {
+    return builder.create(struct: obj)
+  }
+}
+
 public struct Attacker: FlatBufferObject, Verifiable, ObjectAPIPacker {
 
   static func validateVersion() { FlatBuffersVersion_2_0_0() }
@@ -289,6 +404,88 @@ public class AttackerT: NativeObject {
   public func serialize() -> ByteBuffer { return serialize(type: Attacker.self) }
 
 }
+public struct HandFan: FlatBufferObject, Verifiable, ObjectAPIPacker {
+
+  static func validateVersion() { FlatBuffersVersion_2_0_0() }
+  public var __buffer: ByteBuffer! { return _accessor.bb }
+  private var _accessor: Table
+
+  public static func finish(_ fbb: inout FlatBufferBuilder, end: Offset, prefix: Bool = false) { fbb.finish(offset: end, fileId: "MOVI", addPrefix: prefix) }
+  public static func getRootAsHandFan(bb: ByteBuffer) -> HandFan { return HandFan(Table(bb: bb, position: Int32(bb.read(def: UOffset.self, position: bb.reader)) + Int32(bb.reader))) }
+
+  private init(_ t: Table) { _accessor = t }
+  public init(_ bb: ByteBuffer, o: Int32) { _accessor = Table(bb: bb, position: o) }
+
+  private enum VTOFFSET: VOffset {
+    case length = 4
+    var v: Int32 { Int32(self.rawValue) }
+    var p: VOffset { self.rawValue }
+  }
+
+  public var length: Int32 { let o = _accessor.offset(VTOFFSET.length.v); return o == 0 ? 0 : _accessor.readBuffer(of: Int32.self, at: o) }
+  @discardableResult public func mutate(length: Int32) -> Bool {let o = _accessor.offset(VTOFFSET.length.v);  return _accessor.mutate(length, index: o) }
+  public static func startHandFan(_ fbb: inout FlatBufferBuilder) -> UOffset { fbb.startTable(with: 1) }
+  public static func add(length: Int32, _ fbb: inout FlatBufferBuilder) { fbb.add(element: length, def: 0, at: VTOFFSET.length.p) }
+  public static func endHandFan(_ fbb: inout FlatBufferBuilder, start: UOffset) -> Offset { let end = Offset(offset: fbb.endTable(at: start)); return end }
+  public static func createHandFan(
+    _ fbb: inout FlatBufferBuilder,
+    length: Int32 = 0
+  ) -> Offset {
+    let __start = HandFan.startHandFan(&fbb)
+    HandFan.add(length: length, &fbb)
+    return HandFan.endHandFan(&fbb, start: __start)
+  }
+  
+
+  public mutating func unpack() -> HandFanT {
+    return HandFanT(&self)
+  }
+  public static func pack(_ builder: inout FlatBufferBuilder, obj: inout HandFanT?) -> Offset {
+    guard var obj = obj else { return Offset() }
+    return pack(&builder, obj: &obj)
+  }
+
+  public static func pack(_ builder: inout FlatBufferBuilder, obj: inout HandFanT) -> Offset {
+    let __root = HandFan.startHandFan(&builder)
+    HandFan.add(length: obj.length, &builder)
+    return HandFan.endHandFan(&builder, start: __root)
+  }
+
+  public static func verify<T>(_ verifier: inout Verifier, at position: Int, of type: T.Type) throws where T: Verifiable {
+    var _v = try verifier.visitTable(at: position)
+    try _v.visit(field: VTOFFSET.length.p, fieldName: "length", required: false, type: Int32.self)
+    _v.finish()
+  }
+}
+
+extension HandFan: Encodable {
+
+  enum CodingKeys: String, CodingKey {
+    case length = "length"
+  }
+  public func encode(to encoder: Encoder) throws {
+    var container = encoder.container(keyedBy: CodingKeys.self)
+    if length != 0 {
+      try container.encodeIfPresent(length, forKey: .length)
+    }
+  }
+}
+
+public class HandFanT: NativeObject {
+
+  public var length: Int32
+
+  public init(_ _t: inout HandFan) {
+    length = _t.length
+  }
+
+  public init() {
+    length = 0
+  }
+
+  public func serialize() -> ByteBuffer { return serialize(type: HandFan.self) }
+
+}
 public struct Movie: FlatBufferObject, Verifiable, ObjectAPIPacker {
 
   static func validateVersion() { FlatBuffersVersion_2_0_0() }
diff --git a/tests/cpp17/generated_cpp17/monster_test_generated.h b/tests/cpp17/generated_cpp17/monster_test_generated.h
index 430d7aaf..db45b604 100644
--- a/tests/cpp17/generated_cpp17/monster_test_generated.h
+++ b/tests/cpp17/generated_cpp17/monster_test_generated.h
@@ -212,6 +212,22 @@ template<> struct AnyTraits<MyGame::Example2::Monster> {
   static const Any enum_value = Any::MyGame_Example2_Monster;
 };
 
+template<typename T> struct AnyUnionTraits {
+  static const Any enum_value = Any::NONE;
+};
+
+template<> struct AnyUnionTraits<MyGame::Example::MonsterT> {
+  static const Any enum_value = Any::Monster;
+};
+
+template<> struct AnyUnionTraits<MyGame::Example::TestSimpleTableWithEnumT> {
+  static const Any enum_value = Any::TestSimpleTableWithEnum;
+};
+
+template<> struct AnyUnionTraits<MyGame::Example2::MonsterT> {
+  static const Any enum_value = Any::MyGame_Example2_Monster;
+};
+
 struct AnyUnion {
   Any type;
   void *value;
@@ -231,9 +247,9 @@ struct AnyUnion {
 
   template <typename T>
   void Set(T&& val) {
-    using RT = typename std::remove_reference<T>::type;
+    typedef typename std::remove_reference<T>::type RT;
     Reset();
-    type = AnyTraits<typename RT::TableType>::enum_value;
+    type = AnyUnionTraits<RT>::enum_value;
     if (type != Any::NONE) {
       value = new RT(std::forward<T>(val));
     }
@@ -323,6 +339,22 @@ template<> struct AnyUniqueAliasesTraits<MyGame::Example2::Monster> {
   static const AnyUniqueAliases enum_value = AnyUniqueAliases::M2;
 };
 
+template<typename T> struct AnyUniqueAliasesUnionTraits {
+  static const AnyUniqueAliases enum_value = AnyUniqueAliases::NONE;
+};
+
+template<> struct AnyUniqueAliasesUnionTraits<MyGame::Example::MonsterT> {
+  static const AnyUniqueAliases enum_value = AnyUniqueAliases::M;
+};
+
+template<> struct AnyUniqueAliasesUnionTraits<MyGame::Example::TestSimpleTableWithEnumT> {
+  static const AnyUniqueAliases enum_value = AnyUniqueAliases::TS;
+};
+
+template<> struct AnyUniqueAliasesUnionTraits<MyGame::Example2::MonsterT> {
+  static const AnyUniqueAliases enum_value = AnyUniqueAliases::M2;
+};
+
 struct AnyUniqueAliasesUnion {
   AnyUniqueAliases type;
   void *value;
@@ -342,9 +374,9 @@ struct AnyUniqueAliasesUnion {
 
   template <typename T>
   void Set(T&& val) {
-    using RT = typename std::remove_reference<T>::type;
+    typedef typename std::remove_reference<T>::type RT;
     Reset();
-    type = AnyUniqueAliasesTraits<typename RT::TableType>::enum_value;
+    type = AnyUniqueAliasesUnionTraits<RT>::enum_value;
     if (type != AnyUniqueAliases::NONE) {
       value = new RT(std::forward<T>(val));
     }
@@ -2936,6 +2968,7 @@ inline bool VerifyAnyVector(flatbuffers::Verifier &verifier, const flatbuffers::
 }
 
 inline void *AnyUnion::UnPack(const void *obj, Any type, const flatbuffers::resolver_function_t *resolver) {
+  (void)resolver;
   switch (type) {
     case Any::Monster: {
       auto ptr = reinterpret_cast<const MyGame::Example::Monster *>(obj);
@@ -2954,6 +2987,7 @@ inline void *AnyUnion::UnPack(const void *obj, Any type, const flatbuffers::reso
 }
 
 inline flatbuffers::Offset<void> AnyUnion::Pack(flatbuffers::FlatBufferBuilder &_fbb, const flatbuffers::rehasher_function_t *_rehasher) const {
+  (void)_rehasher;
   switch (type) {
     case Any::Monster: {
       auto ptr = reinterpret_cast<const MyGame::Example::MonsterT *>(value);
@@ -3047,6 +3081,7 @@ inline bool VerifyAnyUniqueAliasesVector(flatbuffers::Verifier &verifier, const
 }
 
 inline void *AnyUniqueAliasesUnion::UnPack(const void *obj, AnyUniqueAliases type, const flatbuffers::resolver_function_t *resolver) {
+  (void)resolver;
   switch (type) {
     case AnyUniqueAliases::M: {
       auto ptr = reinterpret_cast<const MyGame::Example::Monster *>(obj);
@@ -3065,6 +3100,7 @@ inline void *AnyUniqueAliasesUnion::UnPack(const void *obj, AnyUniqueAliases typ
 }
 
 inline flatbuffers::Offset<void> AnyUniqueAliasesUnion::Pack(flatbuffers::FlatBufferBuilder &_fbb, const flatbuffers::rehasher_function_t *_rehasher) const {
+  (void)_rehasher;
   switch (type) {
     case AnyUniqueAliases::M: {
       auto ptr = reinterpret_cast<const MyGame::Example::MonsterT *>(value);
@@ -3158,6 +3194,7 @@ inline bool VerifyAnyAmbiguousAliasesVector(flatbuffers::Verifier &verifier, con
 }
 
 inline void *AnyAmbiguousAliasesUnion::UnPack(const void *obj, AnyAmbiguousAliases type, const flatbuffers::resolver_function_t *resolver) {
+  (void)resolver;
   switch (type) {
     case AnyAmbiguousAliases::M1: {
       auto ptr = reinterpret_cast<const MyGame::Example::Monster *>(obj);
@@ -3176,6 +3213,7 @@ inline void *AnyAmbiguousAliasesUnion::UnPack(const void *obj, AnyAmbiguousAlias
 }
 
 inline flatbuffers::Offset<void> AnyAmbiguousAliasesUnion::Pack(flatbuffers::FlatBufferBuilder &_fbb, const flatbuffers::rehasher_function_t *_rehasher) const {
+  (void)_rehasher;
   switch (type) {
     case AnyAmbiguousAliases::M1: {
       auto ptr = reinterpret_cast<const MyGame::Example::MonsterT *>(value);
diff --git a/tests/cpp17/generated_cpp17/union_vector_generated.h b/tests/cpp17/generated_cpp17/union_vector_generated.h
index b8b8fb5d..6b794fb2 100644
--- a/tests/cpp17/generated_cpp17/union_vector_generated.h
+++ b/tests/cpp17/generated_cpp17/union_vector_generated.h
@@ -14,6 +14,12 @@ struct Rapunzel;
 
 struct BookReader;
 
+struct FallingTub;
+
+struct HandFan;
+struct HandFanBuilder;
+struct HandFanT;
+
 struct Movie;
 struct MovieBuilder;
 struct MovieT;
@@ -24,6 +30,10 @@ inline const flatbuffers::TypeTable *RapunzelTypeTable();
 
 inline const flatbuffers::TypeTable *BookReaderTypeTable();
 
+inline const flatbuffers::TypeTable *FallingTubTypeTable();
+
+inline const flatbuffers::TypeTable *HandFanTypeTable();
+
 inline const flatbuffers::TypeTable *MovieTypeTable();
 
 enum class Character : uint8_t {
@@ -144,6 +154,114 @@ struct CharacterUnion {
 bool VerifyCharacter(flatbuffers::Verifier &verifier, const void *obj, Character type);
 bool VerifyCharacterVector(flatbuffers::Verifier &verifier, const flatbuffers::Vector<flatbuffers::Offset<void>> *values, const flatbuffers::Vector<Character> *types);
 
+enum class Gadget : uint8_t {
+  NONE = 0,
+  FallingTub = 1,
+  HandFan = 2,
+  MIN = NONE,
+  MAX = HandFan
+};
+
+inline const Gadget (&EnumValuesGadget())[3] {
+  static const Gadget values[] = {
+    Gadget::NONE,
+    Gadget::FallingTub,
+    Gadget::HandFan
+  };
+  return values;
+}
+
+inline const char * const *EnumNamesGadget() {
+  static const char * const names[4] = {
+    "NONE",
+    "FallingTub",
+    "HandFan",
+    nullptr
+  };
+  return names;
+}
+
+inline const char *EnumNameGadget(Gadget e) {
+  if (flatbuffers::IsOutRange(e, Gadget::NONE, Gadget::HandFan)) return "";
+  const size_t index = static_cast<size_t>(e);
+  return EnumNamesGadget()[index];
+}
+
+template<typename T> struct GadgetTraits {
+  static const Gadget enum_value = Gadget::NONE;
+};
+
+template<> struct GadgetTraits<FallingTub> {
+  static const Gadget enum_value = Gadget::FallingTub;
+};
+
+template<> struct GadgetTraits<HandFan> {
+  static const Gadget enum_value = Gadget::HandFan;
+};
+
+template<typename T> struct GadgetUnionTraits {
+  static const Gadget enum_value = Gadget::NONE;
+};
+
+template<> struct GadgetUnionTraits<FallingTub> {
+  static const Gadget enum_value = Gadget::FallingTub;
+};
+
+template<> struct GadgetUnionTraits<HandFanT> {
+  static const Gadget enum_value = Gadget::HandFan;
+};
+
+struct GadgetUnion {
+  Gadget type;
+  void *value;
+
+  GadgetUnion() : type(Gadget::NONE), value(nullptr) {}
+  GadgetUnion(GadgetUnion&& u) FLATBUFFERS_NOEXCEPT :
+    type(Gadget::NONE), value(nullptr)
+    { std::swap(type, u.type); std::swap(value, u.value); }
+  GadgetUnion(const GadgetUnion &);
+  GadgetUnion &operator=(const GadgetUnion &u)
+    { GadgetUnion t(u); std::swap(type, t.type); std::swap(value, t.value); return *this; }
+  GadgetUnion &operator=(GadgetUnion &&u) FLATBUFFERS_NOEXCEPT
+    { std::swap(type, u.type); std::swap(value, u.value); return *this; }
+  ~GadgetUnion() { Reset(); }
+
+  void Reset();
+
+  template <typename T>
+  void Set(T&& val) {
+    typedef typename std::remove_reference<T>::type RT;
+    Reset();
+    type = GadgetUnionTraits<RT>::enum_value;
+    if (type != Gadget::NONE) {
+      value = new RT(std::forward<T>(val));
+    }
+  }
+
+  static void *UnPack(const void *obj, Gadget type, const flatbuffers::resolver_function_t *resolver);
+  flatbuffers::Offset<void> Pack(flatbuffers::FlatBufferBuilder &_fbb, const flatbuffers::rehasher_function_t *_rehasher = nullptr) const;
+
+  FallingTub *AsFallingTub() {
+    return type == Gadget::FallingTub ?
+      reinterpret_cast<FallingTub *>(value) : nullptr;
+  }
+  const FallingTub *AsFallingTub() const {
+    return type == Gadget::FallingTub ?
+      reinterpret_cast<const FallingTub *>(value) : nullptr;
+  }
+  HandFanT *AsHandFan() {
+    return type == Gadget::HandFan ?
+      reinterpret_cast<HandFanT *>(value) : nullptr;
+  }
+  const HandFanT *AsHandFan() const {
+    return type == Gadget::HandFan ?
+      reinterpret_cast<const HandFanT *>(value) : nullptr;
+  }
+};
+
+bool VerifyGadget(flatbuffers::Verifier &verifier, const void *obj, Gadget type);
+bool VerifyGadgetVector(flatbuffers::Verifier &verifier, const flatbuffers::Vector<flatbuffers::Offset<void>> *values, const flatbuffers::Vector<Gadget> *types);
+
 FLATBUFFERS_MANUALLY_ALIGNED_STRUCT(4) Rapunzel FLATBUFFERS_FINAL_CLASS {
  private:
   int32_t hair_length_;
@@ -226,6 +344,47 @@ struct BookReader::Traits {
   using FieldType = decltype(std::declval<type>().get_field<Index>());
 };
 
+FLATBUFFERS_MANUALLY_ALIGNED_STRUCT(4) FallingTub FLATBUFFERS_FINAL_CLASS {
+ private:
+  int32_t weight_;
+
+ public:
+  struct Traits;
+  static const flatbuffers::TypeTable *MiniReflectTypeTable() {
+    return FallingTubTypeTable();
+  }
+  FallingTub()
+      : weight_(0) {
+  }
+  FallingTub(int32_t _weight)
+      : weight_(flatbuffers::EndianScalar(_weight)) {
+  }
+  int32_t weight() const {
+    return flatbuffers::EndianScalar(weight_);
+  }
+  void mutate_weight(int32_t _weight) {
+    flatbuffers::WriteScalar(&weight_, _weight);
+  }
+  template<size_t Index>
+  auto get_field() const {
+         if constexpr (Index == 0) return weight();
+    else static_assert(Index != Index, "Invalid Field Index");
+  }
+};
+FLATBUFFERS_STRUCT_END(FallingTub, 4);
+
+struct FallingTub::Traits {
+  using type = FallingTub;
+  static constexpr auto name = "FallingTub";
+  static constexpr auto fully_qualified_name = "FallingTub";
+  static constexpr size_t fields_number = 1;
+  static constexpr std::array<const char *, fields_number> field_names = {
+    "weight"
+  };
+  template<size_t Index>
+  using FieldType = decltype(std::declval<type>().get_field<Index>());
+};
+
 struct AttackerT : public flatbuffers::NativeTable {
   typedef Attacker TableType;
   int32_t sword_attack_damage = 0;
@@ -303,6 +462,83 @@ struct Attacker::Traits {
 
 flatbuffers::Offset<Attacker> CreateAttacker(flatbuffers::FlatBufferBuilder &_fbb, const AttackerT *_o, const flatbuffers::rehasher_function_t *_rehasher = nullptr);
 
+struct HandFanT : public flatbuffers::NativeTable {
+  typedef HandFan TableType;
+  int32_t length = 0;
+};
+
+struct HandFan FLATBUFFERS_FINAL_CLASS : private flatbuffers::Table {
+  typedef HandFanT NativeTableType;
+  typedef HandFanBuilder Builder;
+  struct Traits;
+  static const flatbuffers::TypeTable *MiniReflectTypeTable() {
+    return HandFanTypeTable();
+  }
+  enum FlatBuffersVTableOffset FLATBUFFERS_VTABLE_UNDERLYING_TYPE {
+    VT_LENGTH = 4
+  };
+  int32_t length() const {
+    return GetField<int32_t>(VT_LENGTH, 0);
+  }
+  bool mutate_length(int32_t _length = 0) {
+    return SetField<int32_t>(VT_LENGTH, _length, 0);
+  }
+  template<size_t Index>
+  auto get_field() const {
+         if constexpr (Index == 0) return length();
+    else static_assert(Index != Index, "Invalid Field Index");
+  }
+  bool Verify(flatbuffers::Verifier &verifier) const {
+    return VerifyTableStart(verifier) &&
+           VerifyField<int32_t>(verifier, VT_LENGTH) &&
+           verifier.EndTable();
+  }
+  HandFanT *UnPack(const flatbuffers::resolver_function_t *_resolver = nullptr) const;
+  void UnPackTo(HandFanT *_o, const flatbuffers::resolver_function_t *_resolver = nullptr) const;
+  static flatbuffers::Offset<HandFan> Pack(flatbuffers::FlatBufferBuilder &_fbb, const HandFanT* _o, const flatbuffers::rehasher_function_t *_rehasher = nullptr);
+};
+
+struct HandFanBuilder {
+  typedef HandFan Table;
+  flatbuffers::FlatBufferBuilder &fbb_;
+  flatbuffers::uoffset_t start_;
+  void add_length(int32_t length) {
+    fbb_.AddElement<int32_t>(HandFan::VT_LENGTH, length, 0);
+  }
+  explicit HandFanBuilder(flatbuffers::FlatBufferBuilder &_fbb)
+        : fbb_(_fbb) {
+    start_ = fbb_.StartTable();
+  }
+  flatbuffers::Offset<HandFan> Finish() {
+    const auto end = fbb_.EndTable(start_);
+    auto o = flatbuffers::Offset<HandFan>(end);
+    return o;
+  }
+};
+
+inline flatbuffers::Offset<HandFan> CreateHandFan(
+    flatbuffers::FlatBufferBuilder &_fbb,
+    int32_t length = 0) {
+  HandFanBuilder builder_(_fbb);
+  builder_.add_length(length);
+  return builder_.Finish();
+}
+
+struct HandFan::Traits {
+  using type = HandFan;
+  static auto constexpr Create = CreateHandFan;
+  static constexpr auto name = "HandFan";
+  static constexpr auto fully_qualified_name = "HandFan";
+  static constexpr size_t fields_number = 1;
+  static constexpr std::array<const char *, fields_number> field_names = {
+    "length"
+  };
+  template<size_t Index>
+  using FieldType = decltype(std::declval<type>().get_field<Index>());
+};
+
+flatbuffers::Offset<HandFan> CreateHandFan(flatbuffers::FlatBufferBuilder &_fbb, const HandFanT *_o, const flatbuffers::rehasher_function_t *_rehasher = nullptr);
+
 struct MovieT : public flatbuffers::NativeTable {
   typedef Movie TableType;
   CharacterUnion main_character{};
@@ -487,6 +723,32 @@ inline flatbuffers::Offset<Attacker> CreateAttacker(flatbuffers::FlatBufferBuild
       _sword_attack_damage);
 }
 
+inline HandFanT *HandFan::UnPack(const flatbuffers::resolver_function_t *_resolver) const {
+  auto _o = std::make_unique<HandFanT>();
+  UnPackTo(_o.get(), _resolver);
+  return _o.release();
+}
+
+inline void HandFan::UnPackTo(HandFanT *_o, const flatbuffers::resolver_function_t *_resolver) const {
+  (void)_o;
+  (void)_resolver;
+  { auto _e = length(); _o->length = _e; }
+}
+
+inline flatbuffers::Offset<HandFan> HandFan::Pack(flatbuffers::FlatBufferBuilder &_fbb, const HandFanT* _o, const flatbuffers::rehasher_function_t *_rehasher) {
+  return CreateHandFan(_fbb, _o, _rehasher);
+}
+
+inline flatbuffers::Offset<HandFan> CreateHandFan(flatbuffers::FlatBufferBuilder &_fbb, const HandFanT *_o, const flatbuffers::rehasher_function_t *_rehasher) {
+  (void)_rehasher;
+  (void)_o;
+  struct _VectorArgs { flatbuffers::FlatBufferBuilder *__fbb; const HandFanT* __o; const flatbuffers::rehasher_function_t *__rehasher; } _va = { &_fbb, _o, _rehasher}; (void)_va;
+  auto _length = _o->length;
+  return CreateHandFan(
+      _fbb,
+      _length);
+}
+
 inline MovieT *Movie::UnPack(const flatbuffers::resolver_function_t *_resolver) const {
   auto _o = std::make_unique<MovieT>();
   UnPackTo(_o.get(), _resolver);
@@ -565,6 +827,7 @@ inline bool VerifyCharacterVector(flatbuffers::Verifier &verifier, const flatbuf
 }
 
 inline void *CharacterUnion::UnPack(const void *obj, Character type, const flatbuffers::resolver_function_t *resolver) {
+  (void)resolver;
   switch (type) {
     case Character::MuLan: {
       auto ptr = reinterpret_cast<const Attacker *>(obj);
@@ -595,6 +858,7 @@ inline void *CharacterUnion::UnPack(const void *obj, Character type, const flatb
 }
 
 inline flatbuffers::Offset<void> CharacterUnion::Pack(flatbuffers::FlatBufferBuilder &_fbb, const flatbuffers::rehasher_function_t *_rehasher) const {
+  (void)_rehasher;
   switch (type) {
     case Character::MuLan: {
       auto ptr = reinterpret_cast<const AttackerT *>(value);
@@ -693,6 +957,97 @@ inline void CharacterUnion::Reset() {
   type = Character::NONE;
 }
 
+inline bool VerifyGadget(flatbuffers::Verifier &verifier, const void *obj, Gadget type) {
+  switch (type) {
+    case Gadget::NONE: {
+      return true;
+    }
+    case Gadget::FallingTub: {
+      return verifier.Verify<FallingTub>(static_cast<const uint8_t *>(obj), 0);
+    }
+    case Gadget::HandFan: {
+      auto ptr = reinterpret_cast<const HandFan *>(obj);
+      return verifier.VerifyTable(ptr);
+    }
+    default: return true;
+  }
+}
+
+inline bool VerifyGadgetVector(flatbuffers::Verifier &verifier, const flatbuffers::Vector<flatbuffers::Offset<void>> *values, const flatbuffers::Vector<Gadget> *types) {
+  if (!values || !types) return !values && !types;
+  if (values->size() != types->size()) return false;
+  for (flatbuffers::uoffset_t i = 0; i < values->size(); ++i) {
+    if (!VerifyGadget(
+        verifier,  values->Get(i), types->GetEnum<Gadget>(i))) {
+      return false;
+    }
+  }
+  return true;
+}
+
+inline void *GadgetUnion::UnPack(const void *obj, Gadget type, const flatbuffers::resolver_function_t *resolver) {
+  (void)resolver;
+  switch (type) {
+    case Gadget::FallingTub: {
+      auto ptr = reinterpret_cast<const FallingTub *>(obj);
+      return new FallingTub(*ptr);
+    }
+    case Gadget::HandFan: {
+      auto ptr = reinterpret_cast<const HandFan *>(obj);
+      return ptr->UnPack(resolver);
+    }
+    default: return nullptr;
+  }
+}
+
+inline flatbuffers::Offset<void> GadgetUnion::Pack(flatbuffers::FlatBufferBuilder &_fbb, const flatbuffers::rehasher_function_t *_rehasher) const {
+  (void)_rehasher;
+  switch (type) {
+    case Gadget::FallingTub: {
+      auto ptr = reinterpret_cast<const FallingTub *>(value);
+      return _fbb.CreateStruct(*ptr).Union();
+    }
+    case Gadget::HandFan: {
+      auto ptr = reinterpret_cast<const HandFanT *>(value);
+      return CreateHandFan(_fbb, ptr, _rehasher).Union();
+    }
+    default: return 0;
+  }
+}
+
+inline GadgetUnion::GadgetUnion(const GadgetUnion &u) : type(u.type), value(nullptr) {
+  switch (type) {
+    case Gadget::FallingTub: {
+      value = new FallingTub(*reinterpret_cast<FallingTub *>(u.value));
+      break;
+    }
+    case Gadget::HandFan: {
+      value = new HandFanT(*reinterpret_cast<HandFanT *>(u.value));
+      break;
+    }
+    default:
+      break;
+  }
+}
+
+inline void GadgetUnion::Reset() {
+  switch (type) {
+    case Gadget::FallingTub: {
+      auto ptr = reinterpret_cast<FallingTub *>(value);
+      delete ptr;
+      break;
+    }
+    case Gadget::HandFan: {
+      auto ptr = reinterpret_cast<HandFanT *>(value);
+      delete ptr;
+      break;
+    }
+    default: break;
+  }
+  value = nullptr;
+  type = Gadget::NONE;
+}
+
 inline const flatbuffers::TypeTable *CharacterTypeTable() {
   static const flatbuffers::TypeCode type_codes[] = {
     { flatbuffers::ET_SEQUENCE, 0, -1 },
@@ -723,6 +1078,27 @@ inline const flatbuffers::TypeTable *CharacterTypeTable() {
   return &tt;
 }
 
+inline const flatbuffers::TypeTable *GadgetTypeTable() {
+  static const flatbuffers::TypeCode type_codes[] = {
+    { flatbuffers::ET_SEQUENCE, 0, -1 },
+    { flatbuffers::ET_SEQUENCE, 0, 0 },
+    { flatbuffers::ET_SEQUENCE, 0, 1 }
+  };
+  static const flatbuffers::TypeFunction type_refs[] = {
+    FallingTubTypeTable,
+    HandFanTypeTable
+  };
+  static const char * const names[] = {
+    "NONE",
+    "FallingTub",
+    "HandFan"
+  };
+  static const flatbuffers::TypeTable tt = {
+    flatbuffers::ST_UNION, 3, type_codes, type_refs, nullptr, nullptr, names
+  };
+  return &tt;
+}
+
 inline const flatbuffers::TypeTable *AttackerTypeTable() {
   static const flatbuffers::TypeCode type_codes[] = {
     { flatbuffers::ET_INT, 0, -1 }
@@ -764,6 +1140,33 @@ inline const flatbuffers::TypeTable *BookReaderTypeTable() {
   return &tt;
 }
 
+inline const flatbuffers::TypeTable *FallingTubTypeTable() {
+  static const flatbuffers::TypeCode type_codes[] = {
+    { flatbuffers::ET_INT, 0, -1 }
+  };
+  static const int64_t values[] = { 0, 4 };
+  static const char * const names[] = {
+    "weight"
+  };
+  static const flatbuffers::TypeTable tt = {
+    flatbuffers::ST_STRUCT, 1, type_codes, nullptr, nullptr, values, names
+  };
+  return &tt;
+}
+
+inline const flatbuffers::TypeTable *HandFanTypeTable() {
+  static const flatbuffers::TypeCode type_codes[] = {
+    { flatbuffers::ET_INT, 0, -1 }
+  };
+  static const char * const names[] = {
+    "length"
+  };
+  static const flatbuffers::TypeTable tt = {
+    flatbuffers::ST_TABLE, 1, type_codes, nullptr, nullptr, nullptr, names
+  };
+  return &tt;
+}
+
 inline const flatbuffers::TypeTable *MovieTypeTable() {
   static const flatbuffers::TypeCode type_codes[] = {
     { flatbuffers::ET_UTYPE, 0, 0 },
diff --git a/tests/monster_test_generated.h b/tests/monster_test_generated.h
index 598dc902..0345d4b1 100644
--- a/tests/monster_test_generated.h
+++ b/tests/monster_test_generated.h
@@ -242,6 +242,22 @@ template<> struct AnyTraits<MyGame::Example2::Monster> {
   static const Any enum_value = Any_MyGame_Example2_Monster;
 };
 
+template<typename T> struct AnyUnionTraits {
+  static const Any enum_value = Any_NONE;
+};
+
+template<> struct AnyUnionTraits<MyGame::Example::MonsterT> {
+  static const Any enum_value = Any_Monster;
+};
+
+template<> struct AnyUnionTraits<MyGame::Example::TestSimpleTableWithEnumT> {
+  static const Any enum_value = Any_TestSimpleTableWithEnum;
+};
+
+template<> struct AnyUnionTraits<MyGame::Example2::MonsterT> {
+  static const Any enum_value = Any_MyGame_Example2_Monster;
+};
+
 struct AnyUnion {
   Any type;
   void *value;
@@ -261,9 +277,9 @@ struct AnyUnion {
 
   template <typename T>
   void Set(T&& val) {
-    using RT = typename std::remove_reference<T>::type;
+    typedef typename std::remove_reference<T>::type RT;
     Reset();
-    type = AnyTraits<typename RT::TableType>::enum_value;
+    type = AnyUnionTraits<RT>::enum_value;
     if (type != Any_NONE) {
       value = new RT(std::forward<T>(val));
     }
@@ -382,6 +398,22 @@ template<> struct AnyUniqueAliasesTraits<MyGame::Example2::Monster> {
   static const AnyUniqueAliases enum_value = AnyUniqueAliases_M2;
 };
 
+template<typename T> struct AnyUniqueAliasesUnionTraits {
+  static const AnyUniqueAliases enum_value = AnyUniqueAliases_NONE;
+};
+
+template<> struct AnyUniqueAliasesUnionTraits<MyGame::Example::MonsterT> {
+  static const AnyUniqueAliases enum_value = AnyUniqueAliases_M;
+};
+
+template<> struct AnyUniqueAliasesUnionTraits<MyGame::Example::TestSimpleTableWithEnumT> {
+  static const AnyUniqueAliases enum_value = AnyUniqueAliases_TS;
+};
+
+template<> struct AnyUniqueAliasesUnionTraits<MyGame::Example2::MonsterT> {
+  static const AnyUniqueAliases enum_value = AnyUniqueAliases_M2;
+};
+
 struct AnyUniqueAliasesUnion {
   AnyUniqueAliases type;
   void *value;
@@ -401,9 +433,9 @@ struct AnyUniqueAliasesUnion {
 
   template <typename T>
   void Set(T&& val) {
-    using RT = typename std::remove_reference<T>::type;
+    typedef typename std::remove_reference<T>::type RT;
     Reset();
-    type = AnyUniqueAliasesTraits<typename RT::TableType>::enum_value;
+    type = AnyUniqueAliasesUnionTraits<RT>::enum_value;
     if (type != AnyUniqueAliases_NONE) {
       value = new RT(std::forward<T>(val));
     }
@@ -2907,6 +2939,7 @@ inline bool VerifyAnyVector(flatbuffers::Verifier &verifier, const flatbuffers::
 }
 
 inline void *AnyUnion::UnPack(const void *obj, Any type, const flatbuffers::resolver_function_t *resolver) {
+  (void)resolver;
   switch (type) {
     case Any_Monster: {
       auto ptr = reinterpret_cast<const MyGame::Example::Monster *>(obj);
@@ -2925,6 +2958,7 @@ inline void *AnyUnion::UnPack(const void *obj, Any type, const flatbuffers::reso
 }
 
 inline flatbuffers::Offset<void> AnyUnion::Pack(flatbuffers::FlatBufferBuilder &_fbb, const flatbuffers::rehasher_function_t *_rehasher) const {
+  (void)_rehasher;
   switch (type) {
     case Any_Monster: {
       auto ptr = reinterpret_cast<const MyGame::Example::MonsterT *>(value);
@@ -3018,6 +3052,7 @@ inline bool VerifyAnyUniqueAliasesVector(flatbuffers::Verifier &verifier, const
 }
 
 inline void *AnyUniqueAliasesUnion::UnPack(const void *obj, AnyUniqueAliases type, const flatbuffers::resolver_function_t *resolver) {
+  (void)resolver;
   switch (type) {
     case AnyUniqueAliases_M: {
       auto ptr = reinterpret_cast<const MyGame::Example::Monster *>(obj);
@@ -3036,6 +3071,7 @@ inline void *AnyUniqueAliasesUnion::UnPack(const void *obj, AnyUniqueAliases typ
 }
 
 inline flatbuffers::Offset<void> AnyUniqueAliasesUnion::Pack(flatbuffers::FlatBufferBuilder &_fbb, const flatbuffers::rehasher_function_t *_rehasher) const {
+  (void)_rehasher;
   switch (type) {
     case AnyUniqueAliases_M: {
       auto ptr = reinterpret_cast<const MyGame::Example::MonsterT *>(value);
@@ -3129,6 +3165,7 @@ inline bool VerifyAnyAmbiguousAliasesVector(flatbuffers::Verifier &verifier, con
 }
 
 inline void *AnyAmbiguousAliasesUnion::UnPack(const void *obj, AnyAmbiguousAliases type, const flatbuffers::resolver_function_t *resolver) {
+  (void)resolver;
   switch (type) {
     case AnyAmbiguousAliases_M1: {
       auto ptr = reinterpret_cast<const MyGame::Example::Monster *>(obj);
@@ -3147,6 +3184,7 @@ inline void *AnyAmbiguousAliasesUnion::UnPack(const void *obj, AnyAmbiguousAlias
 }
 
 inline flatbuffers::Offset<void> AnyAmbiguousAliasesUnion::Pack(flatbuffers::FlatBufferBuilder &_fbb, const flatbuffers::rehasher_function_t *_rehasher) const {
+  (void)_rehasher;
   switch (type) {
     case AnyAmbiguousAliases_M1: {
       auto ptr = reinterpret_cast<const MyGame::Example::MonsterT *>(value);
diff --git a/tests/namespace_test/namespace_test1_generated.h b/tests/namespace_test/namespace_test1_generated.h
index 0fab792d..ed52a27c 100644
--- a/tests/namespace_test/namespace_test1_generated.h
+++ b/tests/namespace_test/namespace_test1_generated.h
@@ -62,6 +62,14 @@ template<> struct UnionInNestedNSTraits<NamespaceA::NamespaceB::TableInNestedNS>
   static const UnionInNestedNS enum_value = UnionInNestedNS_TableInNestedNS;
 };
 
+template<typename T> struct UnionInNestedNSUnionTraits {
+  static const UnionInNestedNS enum_value = UnionInNestedNS_NONE;
+};
+
+template<> struct UnionInNestedNSUnionTraits<NamespaceA::NamespaceB::TableInNestedNST> {
+  static const UnionInNestedNS enum_value = UnionInNestedNS_TableInNestedNS;
+};
+
 struct UnionInNestedNSUnion {
   UnionInNestedNS type;
   void *value;
@@ -81,9 +89,9 @@ struct UnionInNestedNSUnion {
 
   template <typename T>
   void Set(T&& val) {
-    using RT = typename std::remove_reference<T>::type;
+    typedef typename std::remove_reference<T>::type RT;
     Reset();
-    type = UnionInNestedNSTraits<typename RT::TableType>::enum_value;
+    type = UnionInNestedNSUnionTraits<RT>::enum_value;
     if (type != UnionInNestedNS_NONE) {
       value = new RT(std::forward<T>(val));
     }
@@ -332,6 +340,7 @@ inline bool VerifyUnionInNestedNSVector(flatbuffers::Verifier &verifier, const f
 }
 
 inline void *UnionInNestedNSUnion::UnPack(const void *obj, UnionInNestedNS type, const flatbuffers::resolver_function_t *resolver) {
+  (void)resolver;
   switch (type) {
     case UnionInNestedNS_TableInNestedNS: {
       auto ptr = reinterpret_cast<const NamespaceA::NamespaceB::TableInNestedNS *>(obj);
@@ -342,6 +351,7 @@ inline void *UnionInNestedNSUnion::UnPack(const void *obj, UnionInNestedNS type,
 }
 
 inline flatbuffers::Offset<void> UnionInNestedNSUnion::Pack(flatbuffers::FlatBufferBuilder &_fbb, const flatbuffers::rehasher_function_t *_rehasher) const {
+  (void)_rehasher;
   switch (type) {
     case UnionInNestedNS_TableInNestedNS: {
       auto ptr = reinterpret_cast<const NamespaceA::NamespaceB::TableInNestedNST *>(value);
diff --git a/tests/test.cpp b/tests/test.cpp
index e5ec7b12..95be015f 100644
--- a/tests/test.cpp
+++ b/tests/test.cpp
@@ -21,7 +21,6 @@
 #include "flatbuffers/minireflect.h"
 #include "flatbuffers/registry.h"
 #include "flatbuffers/util.h"
-
 #include "monster_test_generated.h"
 #include "namespace_test/namespace_test1_generated.h"
 #include "namespace_test/namespace_test2_generated.h"
@@ -2933,6 +2932,15 @@ void UnionVectorTest() {
   TEST_EQ(parser2.Parse("{a_type:Bool,a:{b:true}}"), true);
 }
 
+void StructUnionTest() {
+  GadgetUnion gadget;
+  gadget.Set(FallingTub(100));
+
+  HandFanT fan;
+  fan.length = 10;
+  gadget.Set(fan);
+}
+
 void ConformTest() {
   flatbuffers::Parser parser;
   TEST_EQ(parser.Parse("table T { A:int; } enum E:byte { A }"), true);
@@ -4187,6 +4195,7 @@ int FlatBufferTests() {
   FlexBuffersFloatingPointTest();
   FlatbuffersIteratorsTest();
   FixedLengthArraySpanTest();
+  StructUnionTest();
   return 0;
 }
 
diff --git a/tests/union_vector/FallingTub.cs b/tests/union_vector/FallingTub.cs
new file mode 100644
index 00000000..36c574c9
--- /dev/null
+++ b/tests/union_vector/FallingTub.cs
@@ -0,0 +1,49 @@
+// <auto-generated>
+//  automatically generated by the FlatBuffers compiler, do not modify
+// </auto-generated>
+
+using global::System;
+using global::System.Collections.Generic;
+using global::FlatBuffers;
+
+public struct FallingTub : IFlatbufferObject
+{
+  private Struct __p;
+  public ByteBuffer ByteBuffer { get { return __p.bb; } }
+  public void __init(int _i, ByteBuffer _bb) { __p = new Struct(_i, _bb); }
+  public FallingTub __assign(int _i, ByteBuffer _bb) { __init(_i, _bb); return this; }
+
+  public int Weight { get { return __p.bb.GetInt(__p.bb_pos + 0); } }
+  public void MutateWeight(int weight) { __p.bb.PutInt(__p.bb_pos + 0, weight); }
+
+  public static Offset<FallingTub> CreateFallingTub(FlatBufferBuilder builder, int Weight) {
+    builder.Prep(4, 4);
+    builder.PutInt(Weight);
+    return new Offset<FallingTub>(builder.Offset);
+  }
+  public FallingTubT UnPack() {
+    var _o = new FallingTubT();
+    this.UnPackTo(_o);
+    return _o;
+  }
+  public void UnPackTo(FallingTubT _o) {
+    _o.Weight = this.Weight;
+  }
+  public static Offset<FallingTub> Pack(FlatBufferBuilder builder, FallingTubT _o) {
+    if (_o == null) return default(Offset<FallingTub>);
+    return CreateFallingTub(
+      builder,
+      _o.Weight);
+  }
+}
+
+public class FallingTubT
+{
+  [Newtonsoft.Json.JsonProperty("weight")]
+  public int Weight { get; set; }
+
+  public FallingTubT() {
+    this.Weight = 0;
+  }
+}
+
diff --git a/tests/union_vector/FallingTub.java b/tests/union_vector/FallingTub.java
new file mode 100644
index 00000000..5c2fae3e
--- /dev/null
+++ b/tests/union_vector/FallingTub.java
@@ -0,0 +1,44 @@
+// automatically generated by the FlatBuffers compiler, do not modify
+
+import java.nio.*;
+import java.lang.*;
+import java.util.*;
+import com.google.flatbuffers.*;
+
+@SuppressWarnings("unused")
+public final class FallingTub extends Struct {
+  public void __init(int _i, ByteBuffer _bb) { __reset(_i, _bb); }
+  public FallingTub __assign(int _i, ByteBuffer _bb) { __init(_i, _bb); return this; }
+
+  public int weight() { return bb.getInt(bb_pos + 0); }
+  public void mutateWeight(int weight) { bb.putInt(bb_pos + 0, weight); }
+
+  public static int createFallingTub(FlatBufferBuilder builder, int weight) {
+    builder.prep(4, 4);
+    builder.putInt(weight);
+    return builder.offset();
+  }
+
+  public static final class Vector extends BaseVector {
+    public Vector __assign(int _vector, int _element_size, ByteBuffer _bb) { __reset(_vector, _element_size, _bb); return this; }
+
+    public FallingTub get(int j) { return get(new FallingTub(), j); }
+    public FallingTub get(FallingTub obj, int j) {  return obj.__assign(__element(j), bb); }
+  }
+  public FallingTubT unpack() {
+    FallingTubT _o = new FallingTubT();
+    unpackTo(_o);
+    return _o;
+  }
+  public void unpackTo(FallingTubT _o) {
+    int _oWeight = weight();
+    _o.setWeight(_oWeight);
+  }
+  public static int pack(FlatBufferBuilder builder, FallingTubT _o) {
+    if (_o == null) return 0;
+    return createFallingTub(
+      builder,
+      _o.getWeight());
+  }
+}
+
diff --git a/tests/union_vector/FallingTub.kt b/tests/union_vector/FallingTub.kt
new file mode 100644
index 00000000..5d753ec7
--- /dev/null
+++ b/tests/union_vector/FallingTub.kt
@@ -0,0 +1,27 @@
+// automatically generated by the FlatBuffers compiler, do not modify
+
+import java.nio.*
+import kotlin.math.sign
+import com.google.flatbuffers.*
+
+@Suppress("unused")
+@ExperimentalUnsignedTypes
+class FallingTub : Struct() {
+
+    fun __init(_i: Int, _bb: ByteBuffer)  {
+        __reset(_i, _bb)
+    }
+    fun __assign(_i: Int, _bb: ByteBuffer) : FallingTub {
+        __init(_i, _bb)
+        return this
+    }
+    val weight : Int get() = bb.getInt(bb_pos + 0)
+    fun mutateWeight(weight: Int) : ByteBuffer = bb.putInt(bb_pos + 0, weight)
+    companion object {
+        fun createFallingTub(builder: FlatBufferBuilder, weight: Int) : Int {
+            builder.prep(4, 4)
+            builder.putInt(weight)
+            return builder.offset()
+        }
+    }
+}
diff --git a/tests/union_vector/FallingTub.php b/tests/union_vector/FallingTub.php
new file mode 100644
index 00000000..3a6800d4
--- /dev/null
+++ b/tests/union_vector/FallingTub.php
@@ -0,0 +1,41 @@
+<?php
+// automatically generated by the FlatBuffers compiler, do not modify
+
+use \Google\FlatBuffers\Struct;
+use \Google\FlatBuffers\Table;
+use \Google\FlatBuffers\ByteBuffer;
+use \Google\FlatBuffers\FlatBufferBuilder;
+
+class FallingTub extends Struct
+{
+    /**
+     * @param int $_i offset
+     * @param ByteBuffer $_bb
+     * @return FallingTub
+     **/
+    public function init($_i, ByteBuffer $_bb)
+    {
+        $this->bb_pos = $_i;
+        $this->bb = $_bb;
+        return $this;
+    }
+
+    /**
+     * @return int
+     */
+    public function GetWeight()
+    {
+        return $this->bb->getInt($this->bb_pos + 0);
+    }
+
+
+    /**
+     * @return int offset
+     */
+    public static function createFallingTub(FlatBufferBuilder $builder, $weight)
+    {
+        $builder->prep(4, 4);
+        $builder->putInt($weight);
+        return $builder->offset();
+    }
+}
diff --git a/tests/union_vector/FallingTubT.java b/tests/union_vector/FallingTubT.java
new file mode 100644
index 00000000..0b986993
--- /dev/null
+++ b/tests/union_vector/FallingTubT.java
@@ -0,0 +1,20 @@
+// automatically generated by the FlatBuffers compiler, do not modify
+
+import java.nio.*;
+import java.lang.*;
+import java.util.*;
+import com.google.flatbuffers.*;
+
+public class FallingTubT {
+  private int weight;
+
+  public int getWeight() { return weight; }
+
+  public void setWeight(int weight) { this.weight = weight; }
+
+
+  public FallingTubT() {
+    this.weight = 0;
+  }
+}
+
diff --git a/tests/union_vector/Gadget.cs b/tests/union_vector/Gadget.cs
new file mode 100644
index 00000000..e4770ddd
--- /dev/null
+++ b/tests/union_vector/Gadget.cs
@@ -0,0 +1,78 @@
+// <auto-generated>
+//  automatically generated by the FlatBuffers compiler, do not modify
+// </auto-generated>
+
+[Newtonsoft.Json.JsonConverter(typeof(Newtonsoft.Json.Converters.StringEnumConverter))]
+public enum Gadget : byte
+{
+  NONE = 0,
+  FallingTub = 1,
+  HandFan = 2,
+};
+
+public class GadgetUnion {
+  public Gadget Type { get; set; }
+  public object Value { get; set; }
+
+  public GadgetUnion() {
+    this.Type = Gadget.NONE;
+    this.Value = null;
+  }
+
+  public T As<T>() where T : class { return this.Value as T; }
+  public FallingTubT AsFallingTub() { return this.As<FallingTubT>(); }
+  public static GadgetUnion FromFallingTub(FallingTubT _fallingtub) { return new GadgetUnion{ Type = Gadget.FallingTub, Value = _fallingtub }; }
+  public HandFanT AsHandFan() { return this.As<HandFanT>(); }
+  public static GadgetUnion FromHandFan(HandFanT _handfan) { return new GadgetUnion{ Type = Gadget.HandFan, Value = _handfan }; }
+
+  public static int Pack(FlatBuffers.FlatBufferBuilder builder, GadgetUnion _o) {
+    switch (_o.Type) {
+      default: return 0;
+      case Gadget.FallingTub: return FallingTub.Pack(builder, _o.AsFallingTub()).Value;
+      case Gadget.HandFan: return HandFan.Pack(builder, _o.AsHandFan()).Value;
+    }
+  }
+}
+
+public class GadgetUnion_JsonConverter : Newtonsoft.Json.JsonConverter {
+  public override bool CanConvert(System.Type objectType) {
+    return objectType == typeof(GadgetUnion) || objectType == typeof(System.Collections.Generic.List<GadgetUnion>);
+  }
+  public override void WriteJson(Newtonsoft.Json.JsonWriter writer, object value, Newtonsoft.Json.JsonSerializer serializer) {
+    var _olist = value as System.Collections.Generic.List<GadgetUnion>;
+    if (_olist != null) {
+      writer.WriteStartArray();
+      foreach (var _o in _olist) { this.WriteJson(writer, _o, serializer); }
+      writer.WriteEndArray();
+    } else {
+      this.WriteJson(writer, value as GadgetUnion, serializer);
+    }
+  }
+  public void WriteJson(Newtonsoft.Json.JsonWriter writer, GadgetUnion _o, Newtonsoft.Json.JsonSerializer serializer) {
+    if (_o == null) return;
+    serializer.Serialize(writer, _o.Value);
+  }
+  public override object ReadJson(Newtonsoft.Json.JsonReader reader, System.Type objectType, object existingValue, Newtonsoft.Json.JsonSerializer serializer) {
+    var _olist = existingValue as System.Collections.Generic.List<GadgetUnion>;
+    if (_olist != null) {
+      for (var _j = 0; _j < _olist.Count; ++_j) {
+        reader.Read();
+        _olist[_j] = this.ReadJson(reader, _olist[_j], serializer);
+      }
+      reader.Read();
+      return _olist;
+    } else {
+      return this.ReadJson(reader, existingValue as GadgetUnion, serializer);
+    }
+  }
+  public GadgetUnion ReadJson(Newtonsoft.Json.JsonReader reader, GadgetUnion _o, Newtonsoft.Json.JsonSerializer serializer) {
+    if (_o == null) return null;
+    switch (_o.Type) {
+      default: break;
+      case Gadget.FallingTub: _o.Value = serializer.Deserialize<FallingTubT>(reader); break;
+      case Gadget.HandFan: _o.Value = serializer.Deserialize<HandFanT>(reader); break;
+    }
+    return _o;
+  }
+}
+
diff --git a/tests/union_vector/Gadget.java b/tests/union_vector/Gadget.java
new file mode 100644
index 00000000..effc315c
--- /dev/null
+++ b/tests/union_vector/Gadget.java
@@ -0,0 +1,14 @@
+// automatically generated by the FlatBuffers compiler, do not modify
+
+@SuppressWarnings("unused")
+public final class Gadget {
+  private Gadget() { }
+  public static final byte NONE = 0;
+  public static final byte FallingTub = 1;
+  public static final byte HandFan = 2;
+
+  public static final String[] names = { "NONE", "FallingTub", "HandFan", };
+
+  public static String name(int e) { return names[e]; }
+}
+
diff --git a/tests/union_vector/Gadget.kt b/tests/union_vector/Gadget.kt
new file mode 100644
index 00000000..d6181ab4
--- /dev/null
+++ b/tests/union_vector/Gadget.kt
@@ -0,0 +1,13 @@
+// automatically generated by the FlatBuffers compiler, do not modify
+
+@Suppress("unused")
+@ExperimentalUnsignedTypes
+class Gadget private constructor() {
+    companion object {
+        const val NONE: UByte = 0u
+        const val FallingTub: UByte = 1u
+        const val HandFan: UByte = 2u
+        val names : Array<String> = arrayOf("NONE", "FallingTub", "HandFan")
+        fun name(e: Int) : String = names[e]
+    }
+}
diff --git a/tests/union_vector/Gadget.php b/tests/union_vector/Gadget.php
new file mode 100644
index 00000000..069f82de
--- /dev/null
+++ b/tests/union_vector/Gadget.php
@@ -0,0 +1,23 @@
+<?php
+// automatically generated by the FlatBuffers compiler, do not modify
+
+class Gadget
+{
+    const NONE = 0;
+    const FallingTub = 1;
+    const HandFan = 2;
+
+    private static $names = array(
+        Gadget::NONE=>"NONE",
+        Gadget::FallingTub=>"FallingTub",
+        Gadget::HandFan=>"HandFan",
+    );
+
+    public static function Name($e)
+    {
+        if (!isset(self::$names[$e])) {
+            throw new \Exception();
+        }
+        return self::$names[$e];
+    }
+}
diff --git a/tests/union_vector/GadgetUnion.java b/tests/union_vector/GadgetUnion.java
new file mode 100644
index 00000000..2ac27453
--- /dev/null
+++ b/tests/union_vector/GadgetUnion.java
@@ -0,0 +1,33 @@
+// automatically generated by the FlatBuffers compiler, do not modify
+
+import com.google.flatbuffers.FlatBufferBuilder;
+
+public class GadgetUnion {
+  private byte type;
+  private Object value;
+
+  public byte getType() { return type; }
+
+  public void setType(byte type) { this.type = type; }
+
+  public Object getValue() { return value; }
+
+  public void setValue(Object value) { this.value = value; }
+
+  public GadgetUnion() {
+    this.type = Gadget.NONE;
+    this.value = null;
+  }
+
+  public FallingTubT asFallingTub() { return (FallingTubT) value; }
+  public HandFanT asHandFan() { return (HandFanT) value; }
+
+  public static int pack(FlatBufferBuilder builder, GadgetUnion _o) {
+    switch (_o.type) {
+      case Gadget.FallingTub: return FallingTub.pack(builder, _o.asFallingTub());
+      case Gadget.HandFan: return HandFan.pack(builder, _o.asHandFan());
+      default: return 0;
+    }
+  }
+}
+
diff --git a/tests/union_vector/HandFan.cs b/tests/union_vector/HandFan.cs
new file mode 100644
index 00000000..a888abf3
--- /dev/null
+++ b/tests/union_vector/HandFan.cs
@@ -0,0 +1,60 @@
+// <auto-generated>
+//  automatically generated by the FlatBuffers compiler, do not modify
+// </auto-generated>
+
+using global::System;
+using global::System.Collections.Generic;
+using global::FlatBuffers;
+
+public struct HandFan : IFlatbufferObject
+{
+  private Table __p;
+  public ByteBuffer ByteBuffer { get { return __p.bb; } }
+  public static void ValidateVersion() { FlatBufferConstants.FLATBUFFERS_2_0_0(); }
+  public static HandFan GetRootAsHandFan(ByteBuffer _bb) { return GetRootAsHandFan(_bb, new HandFan()); }
+  public static HandFan GetRootAsHandFan(ByteBuffer _bb, HandFan obj) { return (obj.__assign(_bb.GetInt(_bb.Position) + _bb.Position, _bb)); }
+  public void __init(int _i, ByteBuffer _bb) { __p = new Table(_i, _bb); }
+  public HandFan __assign(int _i, ByteBuffer _bb) { __init(_i, _bb); return this; }
+
+  public int Length { get { int o = __p.__offset(4); return o != 0 ? __p.bb.GetInt(o + __p.bb_pos) : (int)0; } }
+  public bool MutateLength(int length) { int o = __p.__offset(4); if (o != 0) { __p.bb.PutInt(o + __p.bb_pos, length); return true; } else { return false; } }
+
+  public static Offset<HandFan> CreateHandFan(FlatBufferBuilder builder,
+      int length = 0) {
+    builder.StartTable(1);
+    HandFan.AddLength(builder, length);
+    return HandFan.EndHandFan(builder);
+  }
+
+  public static void StartHandFan(FlatBufferBuilder builder) { builder.StartTable(1); }
+  public static void AddLength(FlatBufferBuilder builder, int length) { builder.AddInt(0, length, 0); }
+  public static Offset<HandFan> EndHandFan(FlatBufferBuilder builder) {
+    int o = builder.EndTable();
+    return new Offset<HandFan>(o);
+  }
+  public HandFanT UnPack() {
+    var _o = new HandFanT();
+    this.UnPackTo(_o);
+    return _o;
+  }
+  public void UnPackTo(HandFanT _o) {
+    _o.Length = this.Length;
+  }
+  public static Offset<HandFan> Pack(FlatBufferBuilder builder, HandFanT _o) {
+    if (_o == null) return default(Offset<HandFan>);
+    return CreateHandFan(
+      builder,
+      _o.Length);
+  }
+}
+
+public class HandFanT
+{
+  [Newtonsoft.Json.JsonProperty("length")]
+  public int Length { get; set; }
+
+  public HandFanT() {
+    this.Length = 0;
+  }
+}
+
diff --git a/tests/union_vector/HandFan.java b/tests/union_vector/HandFan.java
new file mode 100644
index 00000000..14b2520d
--- /dev/null
+++ b/tests/union_vector/HandFan.java
@@ -0,0 +1,55 @@
+// automatically generated by the FlatBuffers compiler, do not modify
+
+import java.nio.*;
+import java.lang.*;
+import java.util.*;
+import com.google.flatbuffers.*;
+
+@SuppressWarnings("unused")
+public final class HandFan extends Table {
+  public static void ValidateVersion() { Constants.FLATBUFFERS_2_0_0(); }
+  public static HandFan getRootAsHandFan(ByteBuffer _bb) { return getRootAsHandFan(_bb, new HandFan()); }
+  public static HandFan getRootAsHandFan(ByteBuffer _bb, HandFan obj) { _bb.order(ByteOrder.LITTLE_ENDIAN); return (obj.__assign(_bb.getInt(_bb.position()) + _bb.position(), _bb)); }
+  public void __init(int _i, ByteBuffer _bb) { __reset(_i, _bb); }
+  public HandFan __assign(int _i, ByteBuffer _bb) { __init(_i, _bb); return this; }
+
+  public int length() { int o = __offset(4); return o != 0 ? bb.getInt(o + bb_pos) : 0; }
+  public boolean mutateLength(int length) { int o = __offset(4); if (o != 0) { bb.putInt(o + bb_pos, length); return true; } else { return false; } }
+
+  public static int createHandFan(FlatBufferBuilder builder,
+      int length) {
+    builder.startTable(1);
+    HandFan.addLength(builder, length);
+    return HandFan.endHandFan(builder);
+  }
+
+  public static void startHandFan(FlatBufferBuilder builder) { builder.startTable(1); }
+  public static void addLength(FlatBufferBuilder builder, int length) { builder.addInt(0, length, 0); }
+  public static int endHandFan(FlatBufferBuilder builder) {
+    int o = builder.endTable();
+    return o;
+  }
+
+  public static final class Vector extends BaseVector {
+    public Vector __assign(int _vector, int _element_size, ByteBuffer _bb) { __reset(_vector, _element_size, _bb); return this; }
+
+    public HandFan get(int j) { return get(new HandFan(), j); }
+    public HandFan get(HandFan obj, int j) {  return obj.__assign(__indirect(__element(j), bb), bb); }
+  }
+  public HandFanT unpack() {
+    HandFanT _o = new HandFanT();
+    unpackTo(_o);
+    return _o;
+  }
+  public void unpackTo(HandFanT _o) {
+    int _oLength = length();
+    _o.setLength(_oLength);
+  }
+  public static int pack(FlatBufferBuilder builder, HandFanT _o) {
+    if (_o == null) return 0;
+    return createHandFan(
+      builder,
+      _o.getLength());
+  }
+}
+
diff --git a/tests/union_vector/HandFan.kt b/tests/union_vector/HandFan.kt
new file mode 100644
index 00000000..081597c7
--- /dev/null
+++ b/tests/union_vector/HandFan.kt
@@ -0,0 +1,51 @@
+// automatically generated by the FlatBuffers compiler, do not modify
+
+import java.nio.*
+import kotlin.math.sign
+import com.google.flatbuffers.*
+
+@Suppress("unused")
+@ExperimentalUnsignedTypes
+class HandFan : Table() {
+
+    fun __init(_i: Int, _bb: ByteBuffer)  {
+        __reset(_i, _bb)
+    }
+    fun __assign(_i: Int, _bb: ByteBuffer) : HandFan {
+        __init(_i, _bb)
+        return this
+    }
+    val length : Int
+        get() {
+            val o = __offset(4)
+            return if(o != 0) bb.getInt(o + bb_pos) else 0
+        }
+    fun mutateLength(length: Int) : Boolean {
+        val o = __offset(4)
+        return if (o != 0) {
+            bb.putInt(o + bb_pos, length)
+            true
+        } else {
+            false
+        }
+    }
+    companion object {
+        fun validateVersion() = Constants.FLATBUFFERS_2_0_0()
+        fun getRootAsHandFan(_bb: ByteBuffer): HandFan = getRootAsHandFan(_bb, HandFan())
+        fun getRootAsHandFan(_bb: ByteBuffer, obj: HandFan): HandFan {
+            _bb.order(ByteOrder.LITTLE_ENDIAN)
+            return (obj.__assign(_bb.getInt(_bb.position()) + _bb.position(), _bb))
+        }
+        fun createHandFan(builder: FlatBufferBuilder, length: Int) : Int {
+            builder.startTable(1)
+            addLength(builder, length)
+            return endHandFan(builder)
+        }
+        fun startHandFan(builder: FlatBufferBuilder) = builder.startTable(1)
+        fun addLength(builder: FlatBufferBuilder, length: Int) = builder.addInt(0, length, 0)
+        fun endHandFan(builder: FlatBufferBuilder) : Int {
+            val o = builder.endTable()
+            return o
+        }
+    }
+}
diff --git a/tests/union_vector/HandFan.php b/tests/union_vector/HandFan.php
new file mode 100644
index 00000000..673e336b
--- /dev/null
+++ b/tests/union_vector/HandFan.php
@@ -0,0 +1,92 @@
+<?php
+// automatically generated by the FlatBuffers compiler, do not modify
+
+use \Google\FlatBuffers\Struct;
+use \Google\FlatBuffers\Table;
+use \Google\FlatBuffers\ByteBuffer;
+use \Google\FlatBuffers\FlatBufferBuilder;
+
+class HandFan extends Table
+{
+    /**
+     * @param ByteBuffer $bb
+     * @return HandFan
+     */
+    public static function getRootAsHandFan(ByteBuffer $bb)
+    {
+        $obj = new HandFan();
+        return ($obj->init($bb->getInt($bb->getPosition()) + $bb->getPosition(), $bb));
+    }
+
+    public static function HandFanIdentifier()
+    {
+        return "MOVI";
+    }
+
+    public static function HandFanBufferHasIdentifier(ByteBuffer $buf)
+    {
+        return self::__has_identifier($buf, self::HandFanIdentifier());
+    }
+
+    /**
+     * @param int $_i offset
+     * @param ByteBuffer $_bb
+     * @return HandFan
+     **/
+    public function init($_i, ByteBuffer $_bb)
+    {
+        $this->bb_pos = $_i;
+        $this->bb = $_bb;
+        return $this;
+    }
+
+    /**
+     * @return int
+     */
+    public function getLength()
+    {
+        $o = $this->__offset(4);
+        return $o != 0 ? $this->bb->getInt($o + $this->bb_pos) : 0;
+    }
+
+    /**
+     * @param FlatBufferBuilder $builder
+     * @return void
+     */
+    public static function startHandFan(FlatBufferBuilder $builder)
+    {
+        $builder->StartObject(1);
+    }
+
+    /**
+     * @param FlatBufferBuilder $builder
+     * @return HandFan
+     */
+    public static function createHandFan(FlatBufferBuilder $builder, $length)
+    {
+        $builder->startObject(1);
+        self::addLength($builder, $length);
+        $o = $builder->endObject();
+        return $o;
+    }
+
+    /**
+     * @param FlatBufferBuilder $builder
+     * @param int
+     * @return void
+     */
+    public static function addLength(FlatBufferBuilder $builder, $length)
+    {
+        $builder->addIntX(0, $length, 0);
+    }
+
+    /**
+     * @param FlatBufferBuilder $builder
+     * @return int table offset
+     */
+    public static function endHandFan(FlatBufferBuilder $builder)
+    {
+        $o = $builder->endObject();
+        return $o;
+    }
+}
diff --git a/tests/union_vector/HandFanT.java b/tests/union_vector/HandFanT.java
new file mode 100644
index 00000000..d3b202be
--- /dev/null
+++ b/tests/union_vector/HandFanT.java
@@ -0,0 +1,20 @@
+// automatically generated by the FlatBuffers compiler, do not modify
+
+import java.nio.*;
+import java.lang.*;
+import java.util.*;
+import com.google.flatbuffers.*;
+
+public class HandFanT {
+  private int length;
+
+  public int getLength() { return length; }
+
+  public void setLength(int length) { this.length = length; }
+
+
+  public HandFanT() {
+    this.length = 0;
+  }
+}
+
diff --git a/tests/union_vector/falling-tub.ts b/tests/union_vector/falling-tub.ts
new file mode 100644
index 00000000..3a836b36
--- /dev/null
+++ b/tests/union_vector/falling-tub.ts
@@ -0,0 +1,63 @@
+// automatically generated by the FlatBuffers compiler, do not modify
+
+import * as flatbuffers from 'flatbuffers';
+
+
+
+export class FallingTub {
+  bb: flatbuffers.ByteBuffer|null = null;
+  bb_pos = 0;
+__init(i:number, bb:flatbuffers.ByteBuffer):FallingTub {
+  this.bb_pos = i;
+  this.bb = bb;
+  return this;
+}
+
+weight():number {
+  return this.bb!.readInt32(this.bb_pos);
+}
+
+mutate_weight(value:number):boolean {
+  this.bb!.writeInt32(this.bb_pos + 0, value);
+  return true;
+}
+
+static getFullyQualifiedName():string {
+  return 'FallingTub';
+}
+
+static sizeOf():number {
+  return 4;
+}
+
+static createFallingTub(builder:flatbuffers.Builder, weight: number):flatbuffers.Offset {
+  builder.prep(4, 4);
+  builder.writeInt32(weight);
+  return builder.offset();
+}
+
+
+unpack(): FallingTubT {
+  return new FallingTubT(
+    this.weight()
+  );
+}
+
+
+unpackTo(_o: FallingTubT): void {
+  _o.weight = this.weight();
+}
+}
+
+export class FallingTubT {
+constructor(
+  public weight: number = 0
+){}
+
+
+pack(builder:flatbuffers.Builder): flatbuffers.Offset {
+  return FallingTub.createFallingTub(builder,
+    this.weight
+  );
+}
+}
diff --git a/tests/union_vector/gadget.ts b/tests/union_vector/gadget.ts
new file mode 100644
index 00000000..4d84b0af
--- /dev/null
+++ b/tests/union_vector/gadget.ts
@@ -0,0 +1,37 @@
+// automatically generated by the FlatBuffers compiler, do not modify
+
+import { FallingTub, FallingTubT } from './falling-tub';
+import { HandFan, HandFanT } from './hand-fan';
+
+
+export enum Gadget{
+  NONE = 0,
+  FallingTub = 1,
+  HandFan = 2
+}
+
+export function unionToGadget(
+  type: Gadget,
+  accessor: (obj:FallingTub|HandFan) => FallingTub|HandFan|null
+): FallingTub|HandFan|null {
+  switch(Gadget[type]) {
+    case 'NONE': return null; 
+    case 'FallingTub': return accessor(new FallingTub())! as FallingTub;
+    case 'HandFan': return accessor(new HandFan())! as HandFan;
+    default: return null;
+  }
+}
+
+export function unionListToGadget(
+  type: Gadget, 
+  accessor: (index: number, obj:FallingTub|HandFan) => FallingTub|HandFan|null, 
+  index: number
+): FallingTub|HandFan|null {
+  switch(Gadget[type]) {
+    case 'NONE': return null; 
+    case 'FallingTub': return accessor(index, new FallingTub())! as FallingTub;
+    case 'HandFan': return accessor(index, new HandFan())! as HandFan;
+    default: return null;
+  }
+}
+
diff --git a/tests/union_vector/hand-fan.ts b/tests/union_vector/hand-fan.ts
new file mode 100644
index 00000000..4a770bae
--- /dev/null
+++ b/tests/union_vector/hand-fan.ts
@@ -0,0 +1,87 @@
+// automatically generated by the FlatBuffers compiler, do not modify
+
+import * as flatbuffers from 'flatbuffers';
+
+
+
+export class HandFan {
+  bb: flatbuffers.ByteBuffer|null = null;
+  bb_pos = 0;
+__init(i:number, bb:flatbuffers.ByteBuffer):HandFan {
+  this.bb_pos = i;
+  this.bb = bb;
+  return this;
+}
+
+static getRootAsHandFan(bb:flatbuffers.ByteBuffer, obj?:HandFan):HandFan {
+  return (obj || new HandFan()).__init(bb.readInt32(bb.position()) + bb.position(), bb);
+}
+
+static getSizePrefixedRootAsHandFan(bb:flatbuffers.ByteBuffer, obj?:HandFan):HandFan {
+  bb.setPosition(bb.position() + flatbuffers.SIZE_PREFIX_LENGTH);
+  return (obj || new HandFan()).__init(bb.readInt32(bb.position()) + bb.position(), bb);
+}
+
+length():number {
+  const offset = this.bb!.__offset(this.bb_pos, 4);
+  return offset ? this.bb!.readInt32(this.bb_pos + offset) : 0;
+}
+
+mutate_length(value:number):boolean {
+  const offset = this.bb!.__offset(this.bb_pos, 4);
+
+  if (offset === 0) {
+    return false;
+  }
+
+  this.bb!.writeInt32(this.bb_pos + offset, value);
+  return true;
+}
+
+static getFullyQualifiedName():string {
+  return 'HandFan';
+}
+
+static startHandFan(builder:flatbuffers.Builder) {
+  builder.startObject(1);
+}
+
+static addLength(builder:flatbuffers.Builder, length:number) {
+  builder.addFieldInt32(0, length, 0);
+}
+
+static endHandFan(builder:flatbuffers.Builder):flatbuffers.Offset {
+  const offset = builder.endObject();
+  return offset;
+}
+
+static createHandFan(builder:flatbuffers.Builder, length:number):flatbuffers.Offset {
+  HandFan.startHandFan(builder);
+  HandFan.addLength(builder, length);
+  return HandFan.endHandFan(builder);
+}
+
+unpack(): HandFanT {
+  return new HandFanT(
+    this.length()
+  );
+}
+
+
+unpackTo(_o: HandFanT): void {
+  _o.length = this.length();
+}
+}
+
+export class HandFanT {
+constructor(
+  public length: number = 0
+){}
+
+
+pack(builder:flatbuffers.Builder): flatbuffers.Offset {
+  return HandFan.createHandFan(builder,
+    this.length
+  );
+}
+}
diff --git a/tests/union_vector/union_vector.fbs b/tests/union_vector/union_vector.fbs
index 495076f5..3dd38482 100644
--- a/tests/union_vector/union_vector.fbs
+++ b/tests/union_vector/union_vector.fbs
@@ -22,6 +22,19 @@ union Character {
   Unused: string
 }
 
+struct FallingTub {
+  weight: int;
+}
+
+table HandFan {
+  length: int;
+}
+
+union Gadget {
+  FallingTub,
+  HandFan,
+}
+
 table Movie {
   main_character: Character;
   characters: [Character];
diff --git a/tests/union_vector/union_vector.ts b/tests/union_vector/union_vector.ts
index 3ef0d175..f3a118b7 100644
--- a/tests/union_vector/union_vector.ts
+++ b/tests/union_vector/union_vector.ts
@@ -1,5 +1,8 @@
 export { Attacker, AttackerT } from './attacker';
 export { BookReader, BookReaderT } from './book-reader';
 export { Character, unionToCharacter, unionListToCharacter } from './character';
+export { FallingTub, FallingTubT } from './falling-tub';
+export { Gadget, unionToGadget, unionListToGadget } from './gadget';
+export { HandFan, HandFanT } from './hand-fan';
 export { Movie, MovieT } from './movie';
 export { Rapunzel, RapunzelT } from './rapunzel';
diff --git a/tests/union_vector/union_vector_generated.h b/tests/union_vector/union_vector_generated.h
index dab25888..d705b4b1 100644
--- a/tests/union_vector/union_vector_generated.h
+++ b/tests/union_vector/union_vector_generated.h
@@ -14,6 +14,12 @@ struct Rapunzel;
 
 struct BookReader;
 
+struct FallingTub;
+
+struct HandFan;
+struct HandFanBuilder;
+struct HandFanT;
+
 struct Movie;
 struct MovieBuilder;
 struct MovieT;
@@ -24,6 +30,10 @@ bool operator==(const Rapunzel &lhs, const Rapunzel &rhs);
 bool operator!=(const Rapunzel &lhs, const Rapunzel &rhs);
 bool operator==(const BookReader &lhs, const BookReader &rhs);
 bool operator!=(const BookReader &lhs, const BookReader &rhs);
+bool operator==(const FallingTub &lhs, const FallingTub &rhs);
+bool operator!=(const FallingTub &lhs, const FallingTub &rhs);
+bool operator==(const HandFanT &lhs, const HandFanT &rhs);
+bool operator!=(const HandFanT &lhs, const HandFanT &rhs);
 bool operator==(const MovieT &lhs, const MovieT &rhs);
 bool operator!=(const MovieT &lhs, const MovieT &rhs);
 
@@ -33,6 +43,10 @@ inline const flatbuffers::TypeTable *RapunzelTypeTable();
 
 inline const flatbuffers::TypeTable *BookReaderTypeTable();
 
+inline const flatbuffers::TypeTable *FallingTubTypeTable();
+
+inline const flatbuffers::TypeTable *HandFanTypeTable();
+
 inline const flatbuffers::TypeTable *MovieTypeTable();
 
 enum Character : uint8_t {
@@ -194,6 +208,139 @@ inline bool operator!=(const CharacterUnion &lhs, const CharacterUnion &rhs) {
 bool VerifyCharacter(flatbuffers::Verifier &verifier, const void *obj, Character type);
 bool VerifyCharacterVector(flatbuffers::Verifier &verifier, const flatbuffers::Vector<flatbuffers::Offset<void>> *values, const flatbuffers::Vector<uint8_t> *types);
 
+enum Gadget : uint8_t {
+  Gadget_NONE = 0,
+  Gadget_FallingTub = 1,
+  Gadget_HandFan = 2,
+  Gadget_MIN = Gadget_NONE,
+  Gadget_MAX = Gadget_HandFan
+};
+
+inline const Gadget (&EnumValuesGadget())[3] {
+  static const Gadget values[] = {
+    Gadget_NONE,
+    Gadget_FallingTub,
+    Gadget_HandFan
+  };
+  return values;
+}
+
+inline const char * const *EnumNamesGadget() {
+  static const char * const names[4] = {
+    "NONE",
+    "FallingTub",
+    "HandFan",
+    nullptr
+  };
+  return names;
+}
+
+inline const char *EnumNameGadget(Gadget e) {
+  if (flatbuffers::IsOutRange(e, Gadget_NONE, Gadget_HandFan)) return "";
+  const size_t index = static_cast<size_t>(e);
+  return EnumNamesGadget()[index];
+}
+
+template<typename T> struct GadgetTraits {
+  static const Gadget enum_value = Gadget_NONE;
+};
+
+template<> struct GadgetTraits<FallingTub> {
+  static const Gadget enum_value = Gadget_FallingTub;
+};
+
+template<> struct GadgetTraits<HandFan> {
+  static const Gadget enum_value = Gadget_HandFan;
+};
+
+template<typename T> struct GadgetUnionTraits {
+  static const Gadget enum_value = Gadget_NONE;
+};
+
+template<> struct GadgetUnionTraits<FallingTub> {
+  static const Gadget enum_value = Gadget_FallingTub;
+};
+
+template<> struct GadgetUnionTraits<HandFanT> {
+  static const Gadget enum_value = Gadget_HandFan;
+};
+
+struct GadgetUnion {
+  Gadget type;
+  void *value;
+
+  GadgetUnion() : type(Gadget_NONE), value(nullptr) {}
+  GadgetUnion(GadgetUnion&& u) FLATBUFFERS_NOEXCEPT :
+    type(Gadget_NONE), value(nullptr)
+    { std::swap(type, u.type); std::swap(value, u.value); }
+  GadgetUnion(const GadgetUnion &);
+  GadgetUnion &operator=(const GadgetUnion &u)
+    { GadgetUnion t(u); std::swap(type, t.type); std::swap(value, t.value); return *this; }
+  GadgetUnion &operator=(GadgetUnion &&u) FLATBUFFERS_NOEXCEPT
+    { std::swap(type, u.type); std::swap(value, u.value); return *this; }
+  ~GadgetUnion() { Reset(); }
+
+  void Reset();
+
+  template <typename T>
+  void Set(T&& val) {
+    typedef typename std::remove_reference<T>::type RT;
+    Reset();
+    type = GadgetUnionTraits<RT>::enum_value;
+    if (type != Gadget_NONE) {
+      value = new RT(std::forward<T>(val));
+    }
+  }
+
+  static void *UnPack(const void *obj, Gadget type, const flatbuffers::resolver_function_t *resolver);
+  flatbuffers::Offset<void> Pack(flatbuffers::FlatBufferBuilder &_fbb, const flatbuffers::rehasher_function_t *_rehasher = nullptr) const;
+
+  FallingTub *AsFallingTub() {
+    return type == Gadget_FallingTub ?
+      reinterpret_cast<FallingTub *>(value) : nullptr;
+  }
+  const FallingTub *AsFallingTub() const {
+    return type == Gadget_FallingTub ?
+      reinterpret_cast<const FallingTub *>(value) : nullptr;
+  }
+  HandFanT *AsHandFan() {
+    return type == Gadget_HandFan ?
+      reinterpret_cast<HandFanT *>(value) : nullptr;
+  }
+  const HandFanT *AsHandFan() const {
+    return type == Gadget_HandFan ?
+      reinterpret_cast<const HandFanT *>(value) : nullptr;
+  }
+};
+
+
+inline bool operator==(const GadgetUnion &lhs, const GadgetUnion &rhs) {
+  if (lhs.type != rhs.type) return false;
+  switch (lhs.type) {
+    case Gadget_NONE: {
+      return true;
+    }
+    case Gadget_FallingTub: {
+      return *(reinterpret_cast<const FallingTub *>(lhs.value)) ==
+             *(reinterpret_cast<const FallingTub *>(rhs.value));
+    }
+    case Gadget_HandFan: {
+      return *(reinterpret_cast<const HandFanT *>(lhs.value)) ==
+             *(reinterpret_cast<const HandFanT *>(rhs.value));
+    }
+    default: {
+      return false;
+    }
+  }
+}
+
+inline bool operator!=(const GadgetUnion &lhs, const GadgetUnion &rhs) {
+    return !(lhs == rhs);
+}
+
+bool VerifyGadget(flatbuffers::Verifier &verifier, const void *obj, Gadget type);
+bool VerifyGadgetVector(flatbuffers::Verifier &verifier, const flatbuffers::Vector<flatbuffers::Offset<void>> *values, const flatbuffers::Vector<uint8_t> *types);
+
 FLATBUFFERS_MANUALLY_ALIGNED_STRUCT(4) Rapunzel FLATBUFFERS_FINAL_CLASS {
  private:
   int32_t hair_length_;
@@ -266,6 +413,42 @@ inline bool operator!=(const BookReader &lhs, const BookReader &rhs) {
 }
 
 
+FLATBUFFERS_MANUALLY_ALIGNED_STRUCT(4) FallingTub FLATBUFFERS_FINAL_CLASS {
+ private:
+  int32_t weight_;
+
+ public:
+  static const flatbuffers::TypeTable *MiniReflectTypeTable() {
+    return FallingTubTypeTable();
+  }
+  static FLATBUFFERS_CONSTEXPR_CPP11 const char *GetFullyQualifiedName() {
+    return "FallingTub";
+  }
+  FallingTub()
+      : weight_(0) {
+  }
+  FallingTub(int32_t _weight)
+      : weight_(flatbuffers::EndianScalar(_weight)) {
+  }
+  int32_t weight() const {
+    return flatbuffers::EndianScalar(weight_);
+  }
+  void mutate_weight(int32_t _weight) {
+    flatbuffers::WriteScalar(&weight_, _weight);
+  }
+};
+FLATBUFFERS_STRUCT_END(FallingTub, 4);
+
+inline bool operator==(const FallingTub &lhs, const FallingTub &rhs) {
+  return
+      (lhs.weight() == rhs.weight());
+}
+
+inline bool operator!=(const FallingTub &lhs, const FallingTub &rhs) {
+    return !(lhs == rhs);
+}
+
+
 struct AttackerT : public flatbuffers::NativeTable {
   typedef Attacker TableType;
   static FLATBUFFERS_CONSTEXPR_CPP11 const char *GetFullyQualifiedName() {
@@ -330,6 +513,70 @@ inline flatbuffers::Offset<Attacker> CreateAttacker(
 
 flatbuffers::Offset<Attacker> CreateAttacker(flatbuffers::FlatBufferBuilder &_fbb, const AttackerT *_o, const flatbuffers::rehasher_function_t *_rehasher = nullptr);
 
+struct HandFanT : public flatbuffers::NativeTable {
+  typedef HandFan TableType;
+  static FLATBUFFERS_CONSTEXPR_CPP11 const char *GetFullyQualifiedName() {
+    return "HandFanT";
+  }
+  int32_t length = 0;
+};
+
+struct HandFan FLATBUFFERS_FINAL_CLASS : private flatbuffers::Table {
+  typedef HandFanT NativeTableType;
+  typedef HandFanBuilder Builder;
+  static const flatbuffers::TypeTable *MiniReflectTypeTable() {
+    return HandFanTypeTable();
+  }
+  static FLATBUFFERS_CONSTEXPR_CPP11 const char *GetFullyQualifiedName() {
+    return "HandFan";
+  }
+  enum FlatBuffersVTableOffset FLATBUFFERS_VTABLE_UNDERLYING_TYPE {
+    VT_LENGTH = 4
+  };
+  int32_t length() const {
+    return GetField<int32_t>(VT_LENGTH, 0);
+  }
+  bool mutate_length(int32_t _length = 0) {
+    return SetField<int32_t>(VT_LENGTH, _length, 0);
+  }
+  bool Verify(flatbuffers::Verifier &verifier) const {
+    return VerifyTableStart(verifier) &&
+           VerifyField<int32_t>(verifier, VT_LENGTH) &&
+           verifier.EndTable();
+  }
+  HandFanT *UnPack(const flatbuffers::resolver_function_t *_resolver = nullptr) const;
+  void UnPackTo(HandFanT *_o, const flatbuffers::resolver_function_t *_resolver = nullptr) const;
+  static flatbuffers::Offset<HandFan> Pack(flatbuffers::FlatBufferBuilder &_fbb, const HandFanT* _o, const flatbuffers::rehasher_function_t *_rehasher = nullptr);
+};
+
+struct HandFanBuilder {
+  typedef HandFan Table;
+  flatbuffers::FlatBufferBuilder &fbb_;
+  flatbuffers::uoffset_t start_;
+  void add_length(int32_t length) {
+    fbb_.AddElement<int32_t>(HandFan::VT_LENGTH, length, 0);
+  }
+  explicit HandFanBuilder(flatbuffers::FlatBufferBuilder &_fbb)
+        : fbb_(_fbb) {
+    start_ = fbb_.StartTable();
+  }
+  flatbuffers::Offset<HandFan> Finish() {
+    const auto end = fbb_.EndTable(start_);
+    auto o = flatbuffers::Offset<HandFan>(end);
+    return o;
+  }
+};
+
+inline flatbuffers::Offset<HandFan> CreateHandFan(
+    flatbuffers::FlatBufferBuilder &_fbb,
+    int32_t length = 0) {
+  HandFanBuilder builder_(_fbb);
+  builder_.add_length(length);
+  return builder_.Finish();
+}
+
+flatbuffers::Offset<HandFan> CreateHandFan(flatbuffers::FlatBufferBuilder &_fbb, const HandFanT *_o, const flatbuffers::rehasher_function_t *_rehasher = nullptr);
+
 struct MovieT : public flatbuffers::NativeTable {
   typedef Movie TableType;
   static FLATBUFFERS_CONSTEXPR_CPP11 const char *GetFullyQualifiedName() {
@@ -507,6 +754,43 @@ inline flatbuffers::Offset<Attacker> CreateAttacker(flatbuffers::FlatBufferBuild
 }
 
 
+inline bool operator==(const HandFanT &lhs, const HandFanT &rhs) {
+  return
+      (lhs.length == rhs.length);
+}
+
+inline bool operator!=(const HandFanT &lhs, const HandFanT &rhs) {
+    return !(lhs == rhs);
+}
+
+
+inline HandFanT *HandFan::UnPack(const flatbuffers::resolver_function_t *_resolver) const {
+  auto _o = std::unique_ptr<HandFanT>(new HandFanT());
+  UnPackTo(_o.get(), _resolver);
+  return _o.release();
+}
+
+inline void HandFan::UnPackTo(HandFanT *_o, const flatbuffers::resolver_function_t *_resolver) const {
+  (void)_o;
+  (void)_resolver;
+  { auto _e = length(); _o->length = _e; }
+}
+
+inline flatbuffers::Offset<HandFan> HandFan::Pack(flatbuffers::FlatBufferBuilder &_fbb, const HandFanT* _o, const flatbuffers::rehasher_function_t *_rehasher) {
+  return CreateHandFan(_fbb, _o, _rehasher);
+}
+
+inline flatbuffers::Offset<HandFan> CreateHandFan(flatbuffers::FlatBufferBuilder &_fbb, const HandFanT *_o, const flatbuffers::rehasher_function_t *_rehasher) {
+  (void)_rehasher;
+  (void)_o;
+  struct _VectorArgs { flatbuffers::FlatBufferBuilder *__fbb; const HandFanT* __o; const flatbuffers::rehasher_function_t *__rehasher; } _va = { &_fbb, _o, _rehasher}; (void)_va;
+  auto _length = _o->length;
+  return CreateHandFan(
+      _fbb,
+      _length);
+}
+
+
 inline bool operator==(const MovieT &lhs, const MovieT &rhs) {
   return
       (lhs.main_character == rhs.main_character) &&
@@ -596,6 +880,7 @@ inline bool VerifyCharacterVector(flatbuffers::Verifier &verifier, const flatbuf
 }
 
 inline void *CharacterUnion::UnPack(const void *obj, Character type, const flatbuffers::resolver_function_t *resolver) {
+  (void)resolver;
   switch (type) {
     case Character_MuLan: {
       auto ptr = reinterpret_cast<const Attacker *>(obj);
@@ -626,6 +911,7 @@ inline void *CharacterUnion::UnPack(const void *obj, Character type, const flatb
 }
 
 inline flatbuffers::Offset<void> CharacterUnion::Pack(flatbuffers::FlatBufferBuilder &_fbb, const flatbuffers::rehasher_function_t *_rehasher) const {
+  (void)_rehasher;
   switch (type) {
     case Character_MuLan: {
       auto ptr = reinterpret_cast<const AttackerT *>(value);
@@ -724,6 +1010,97 @@ inline void CharacterUnion::Reset() {
   type = Character_NONE;
 }
 
+inline bool VerifyGadget(flatbuffers::Verifier &verifier, const void *obj, Gadget type) {
+  switch (type) {
+    case Gadget_NONE: {
+      return true;
+    }
+    case Gadget_FallingTub: {
+      return verifier.Verify<FallingTub>(static_cast<const uint8_t *>(obj), 0);
+    }
+    case Gadget_HandFan: {
+      auto ptr = reinterpret_cast<const HandFan *>(obj);
+      return verifier.VerifyTable(ptr);
+    }
+    default: return true;
+  }
+}
+
+inline bool VerifyGadgetVector(flatbuffers::Verifier &verifier, const flatbuffers::Vector<flatbuffers::Offset<void>> *values, const flatbuffers::Vector<uint8_t> *types) {
+  if (!values || !types) return !values && !types;
+  if (values->size() != types->size()) return false;
+  for (flatbuffers::uoffset_t i = 0; i < values->size(); ++i) {
+    if (!VerifyGadget(
+        verifier,  values->Get(i), types->GetEnum<Gadget>(i))) {
+      return false;
+    }
+  }
+  return true;
+}
+
+inline void *GadgetUnion::UnPack(const void *obj, Gadget type, const flatbuffers::resolver_function_t *resolver) {
+  (void)resolver;
+  switch (type) {
+    case Gadget_FallingTub: {
+      auto ptr = reinterpret_cast<const FallingTub *>(obj);
+      return new FallingTub(*ptr);
+    }
+    case Gadget_HandFan: {
+      auto ptr = reinterpret_cast<const HandFan *>(obj);
+      return ptr->UnPack(resolver);
+    }
+    default: return nullptr;
+  }
+}
+
+inline flatbuffers::Offset<void> GadgetUnion::Pack(flatbuffers::FlatBufferBuilder &_fbb, const flatbuffers::rehasher_function_t *_rehasher) const {
+  (void)_rehasher;
+  switch (type) {
+    case Gadget_FallingTub: {
+      auto ptr = reinterpret_cast<const FallingTub *>(value);
+      return _fbb.CreateStruct(*ptr).Union();
+    }
+    case Gadget_HandFan: {
+      auto ptr = reinterpret_cast<const HandFanT *>(value);
+      return CreateHandFan(_fbb, ptr, _rehasher).Union();
+    }
+    default: return 0;
+  }
+}
+
+inline GadgetUnion::GadgetUnion(const GadgetUnion &u) : type(u.type), value(nullptr) {
+  switch (type) {
+    case Gadget_FallingTub: {
+      value = new FallingTub(*reinterpret_cast<FallingTub *>(u.value));
+      break;
+    }
+    case Gadget_HandFan: {
+      value = new HandFanT(*reinterpret_cast<HandFanT *>(u.value));
+      break;
+    }
+    default:
+      break;
+  }
+}
+
+inline void GadgetUnion::Reset() {
+  switch (type) {
+    case Gadget_FallingTub: {
+      auto ptr = reinterpret_cast<FallingTub *>(value);
+      delete ptr;
+      break;
+    }
+    case Gadget_HandFan: {
+      auto ptr = reinterpret_cast<HandFanT *>(value);
+      delete ptr;
+      break;
+    }
+    default: break;
+  }
+  value = nullptr;
+  type = Gadget_NONE;
+}
+
 inline const flatbuffers::TypeTable *CharacterTypeTable() {
   static const flatbuffers::TypeCode type_codes[] = {
     { flatbuffers::ET_SEQUENCE, 0, -1 },
@@ -754,6 +1131,27 @@ inline const flatbuffers::TypeTable *CharacterTypeTable() {
   return &tt;
 }
 
+inline const flatbuffers::TypeTable *GadgetTypeTable() {
+  static const flatbuffers::TypeCode type_codes[] = {
+    { flatbuffers::ET_SEQUENCE, 0, -1 },
+    { flatbuffers::ET_SEQUENCE, 0, 0 },
+    { flatbuffers::ET_SEQUENCE, 0, 1 }
+  };
+  static const flatbuffers::TypeFunction type_refs[] = {
+    FallingTubTypeTable,
+    HandFanTypeTable
+  };
+  static const char * const names[] = {
+    "NONE",
+    "FallingTub",
+    "HandFan"
+  };
+  static const flatbuffers::TypeTable tt = {
+    flatbuffers::ST_UNION, 3, type_codes, type_refs, nullptr, nullptr, names
+  };
+  return &tt;
+}
+
 inline const flatbuffers::TypeTable *AttackerTypeTable() {
   static const flatbuffers::TypeCode type_codes[] = {
     { flatbuffers::ET_INT, 0, -1 }
@@ -795,6 +1193,33 @@ inline const flatbuffers::TypeTable *BookReaderTypeTable() {
   return &tt;
 }
 
+inline const flatbuffers::TypeTable *FallingTubTypeTable() {
+  static const flatbuffers::TypeCode type_codes[] = {
+    { flatbuffers::ET_INT, 0, -1 }
+  };
+  static const int64_t values[] = { 0, 4 };
+  static const char * const names[] = {
+    "weight"
+  };
+  static const flatbuffers::TypeTable tt = {
+    flatbuffers::ST_STRUCT, 1, type_codes, nullptr, nullptr, values, names
+  };
+  return &tt;
+}
+
+inline const flatbuffers::TypeTable *HandFanTypeTable() {
+  static const flatbuffers::TypeCode type_codes[] = {
+    { flatbuffers::ET_INT, 0, -1 }
+  };
+  static const char * const names[] = {
+    "length"
+  };
+  static const flatbuffers::TypeTable tt = {
+    flatbuffers::ST_TABLE, 1, type_codes, nullptr, nullptr, nullptr, names
+  };
+  return &tt;
+}
+
 inline const flatbuffers::TypeTable *MovieTypeTable() {
   static const flatbuffers::TypeCode type_codes[] = {
     { flatbuffers::ET_UTYPE, 0, 0 },