[Dart] Adding FlexBuffers support (#5853)

* Adding FlexBuffers support for Dart language

dart/lib/flex_buffers.dart

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+export 'src/builder.dart';
+export 'src/reference.dart';

dart/lib/src/builder.dart

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+import 'dart:convert';
+import 'dart:typed_data';
+
+import 'types.dart';
+
+/// The main builder class for creation of a FlexBuffer.
+class Builder {
+  ByteData _buffer;
+  List<_StackValue> _stack;
+  List<_StackPointer> _stackPointers;
+  int _offset;
+  bool _finished;
+  Map<String, _StackValue> _stringCache;
+  Map<String, _StackValue> _keyCache;
+  Map<_KeysHash, _StackValue> _keyVectorCache;
+  Map<int, _StackValue> _indirectIntCache;
+  Map<double, _StackValue> _indirectDoubleCache;
+
+  /// Instantiate the builder if you intent to gradually build up the buffer by calling
+  /// add... methods and calling [finish] to receive the the resulting byte array.
+  ///
+  /// The default size of internal buffer is set to 2048. Provide a different value in order to avoid buffer copies.
+  Builder({int size = 2048}) {
+    _buffer = ByteData(size);
+    _stack = [];
+    _stackPointers = [];
+    _offset = 0;
+    _finished = false;
+    _stringCache = {};
+    _keyCache = {};
+    _keyVectorCache = {};
+    _indirectIntCache = {};
+    _indirectDoubleCache = {};
+  }
+
+  /// Use this method in order to turn an object into a FlexBuffer directly.
+  ///
+  /// Use the manual instantiation of the [Builder] and gradual addition of values, if performance is more important than convenience.
+  static ByteBuffer buildFromObject(Object value) {
+    final builder = Builder();
+    builder._add(value);
+    final buffer = builder.finish();
+    final byteData = ByteData(buffer.lengthInBytes);
+    byteData.buffer.asUint8List().setAll(0, buffer);
+    return byteData.buffer;
+  }
+
+  void _add(Object value) {
+    if (value == null) {
+      addNull();
+    } else if (value is bool) {
+      addBool(value);
+    } else if (value is int) {
+      addInt(value);
+    } else if (value is double) {
+      addDouble(value);
+    } else if (value is ByteBuffer) {
+      addBlob(value);
+    } else if (value is String) {
+      addString(value);
+    } else if (value is List<dynamic>) {
+      startVector();
+      for (var i = 0; i < value.length; i++) {
+        _add(value[i]);
+      }
+      end();
+    } else if (value is Map<String, dynamic>) {
+      startMap();
+      value.forEach((key, value) {
+        addKey(key);
+        _add(value);
+      });
+      end();
+    } else {
+      throw UnsupportedError('Value of unexpected type: $value');
+    }
+  }
+
+  /// Use this method if you want to store a null value.
+  ///
+  /// Specifically useful when building up a vector where values can be null.
+  void addNull() {
+    _integrityCheckOnValueAddition();
+    _stack.add(_StackValue.WithNull());
+  }
+
+  /// Adds a string value.
+  void addInt(int value) {
+    _integrityCheckOnValueAddition();
+    _stack.add(_StackValue.WithInt(value));
+  }
+
+  /// Adds a bool value.
+  void addBool(bool value) {
+    _integrityCheckOnValueAddition();
+    _stack.add(_StackValue.WithBool(value));
+  }
+
+  /// Adds a double value.
+  void addDouble(double value) {
+    _integrityCheckOnValueAddition();
+    _stack.add(_StackValue.WithDouble(value));
+  }
+
+  /// Adds a string value.
+  void addString(String value) {
+    _integrityCheckOnValueAddition();
+    if (_stringCache.containsKey(value)) {
+      _stack.add(_stringCache[value]);
+      return;
+    }
+    final utf8String = utf8.encode(value);
+    final length = utf8String.length;
+    final bitWidth = BitWidthUtil.width(length);
+    final byteWidth = _align(bitWidth);
+    _writeInt(length, byteWidth);
+    final stringOffset = _offset;
+    final newOffset = _newOffset(length + 1);
+    _pushBuffer(utf8String);
+    _offset = newOffset;
+    final stackValue = _StackValue.WithOffset(stringOffset, ValueType.String, bitWidth);
+    _stack.add(stackValue);
+    _stringCache[value] = stackValue;
+  }
+
+  /// This methods adds a key to a map and should be followed by an add... value call.
+  ///
+  /// It also implies that you call this method only after you called [startMap].
+  void addKey(String value) {
+    _integrityCheckOnKeyAddition();
+    if (_keyCache.containsKey(value)) {
+      _stack.add(_keyCache[value]);
+      return;
+    }
+    final utf8String = utf8.encode(value);
+    final length = utf8String.length;
+    final keyOffset = _offset;
+    final newOffset = _newOffset(length + 1);
+    _pushBuffer(utf8String);
+    _offset = newOffset;
+    final stackValue = _StackValue.WithOffset(keyOffset, ValueType.Key, BitWidth.width8);
+    _stack.add(stackValue);
+    _keyCache[value] = stackValue;
+  }
+
+  /// Adds a byte array.
+  ///
+  /// This method can be used to store any generic BLOB.
+  void addBlob(ByteBuffer value) {
+    _integrityCheckOnValueAddition();
+    final length = value.lengthInBytes;
+    final bitWidth = BitWidthUtil.width(length);
+    final byteWidth = _align(bitWidth);
+    _writeInt(length, byteWidth);
+    final blobOffset = _offset;
+    final newOffset = _newOffset(length);
+    _pushBuffer(value.asUint8List());
+    _offset = newOffset;
+    final stackValue = _StackValue.WithOffset(blobOffset, ValueType.Blob, bitWidth);
+    _stack.add(stackValue);
+  }
+
+  /// Stores int value indirectly in the buffer.
+  ///
+  /// Adding large integer values indirectly might be beneficial if those values suppose to be store in a vector together with small integer values.
+  /// This is due to the fact that FlexBuffers will add padding to small integer values, if they are stored together with large integer values.
+  /// When we add integer indirectly the vector of ints will contain not the value itself, but only the relative offset to the value.
+  /// By setting the [cache] parameter to true, you make sure that the builder tracks added int value and performs deduplication.
+  void addIntIndirectly(int value, {bool cache = false}) {
+    _integrityCheckOnValueAddition();
+    if (_indirectIntCache.containsKey(value)) {
+      _stack.add(_indirectIntCache[value]);
+      return;
+    }
+    final stackValue = _StackValue.WithInt(value);
+    final byteWidth = _align(stackValue.width);
+    final newOffset = _newOffset(byteWidth);
+    final valueOffset = _offset;
+    _pushBuffer(stackValue.asU8List(stackValue.width));
+    final stackOffset = _StackValue.WithOffset(valueOffset, ValueType.IndirectInt, stackValue.width);
+    _stack.add(stackOffset);
+    _offset = newOffset;
+    if (cache) {
+      _indirectIntCache[value] = stackOffset;
+    }
+  }
+
+  /// Stores double value indirectly in the buffer.
+  ///
+  /// Double are stored as 8 or 4 byte values in FlexBuffers. If they are stored in a mixed vector, values which are smaller than 4 / 8 bytes will be padded.
+  /// When we add double indirectly, the vector will contain not the value itself, but only the relative offset to the value. Which could occupy only 1 or 2 bytes, reducing the odds for unnecessary padding.
+  /// By setting the [cache] parameter to true, you make sure that the builder tracks already added double value and performs deduplication.
+  void addDoubleIndirectly(double value, {bool cache = false}) {
+    _integrityCheckOnValueAddition();
+    if (cache && _indirectDoubleCache.containsKey(value)) {
+      _stack.add(_indirectDoubleCache[value]);
+      return;
+    }
+    final stackValue = _StackValue.WithDouble(value);
+    final byteWidth = _align(stackValue.width);
+    final newOffset = _newOffset(byteWidth);
+    final valueOffset = _offset;
+    _pushBuffer(stackValue.asU8List(stackValue.width));
+    final stackOffset = _StackValue.WithOffset(valueOffset, ValueType.IndirectFloat, stackValue.width);
+    _stack.add(stackOffset);
+    _offset = newOffset;
+    if (cache) {
+      _indirectDoubleCache[value] = stackOffset;
+    }
+  }
+
+  /// This method starts a vector definition and needs to be followed by 0 to n add... value calls.
+  ///
+  /// The vector definition needs to be finished with an [end] call.
+  /// It is also possible to add nested vector or map by calling [startVector] / [startMap].
+  void startVector() {
+    _integrityCheckOnValueAddition();
+    _stackPointers.add(_StackPointer(_stack.length, true));
+  }
+
+  /// This method starts a map definition.
+  ///
+  /// This method call needs to be followed by 0 to n [addKey] +  add... value calls.
+  /// The map definition needs to be finished with an [end] call.
+  /// It is also possible to add nested vector or map by calling [startVector] / [startMap] after calling [addKey].
+  void startMap() {
+    _integrityCheckOnValueAddition();
+    _stackPointers.add(_StackPointer(_stack.length, false));
+  }
+
+  /// Marks that the addition of values to the last vector, or map have ended.
+  void end() {
+    final pointer = _stackPointers.removeLast();
+    if (pointer.isVector) {
+      _endVector(pointer);
+    } else {
+      _sortKeysAndEndMap(pointer);
+    }
+  }
+
+  /// Finish building the FlatBuffer and return array of bytes.
+  ///
+  /// Can be called multiple times, to get the array of bytes.
+  /// After the first call, adding values, or starting vectors / maps will result in an exception.
+  Uint8List finish() {
+    if (_finished == false) {
+      _finish();
+    }
+    return _buffer.buffer.asUint8List(0, _offset);
+  }
+
+  /// Builds a FlatBuffer with current state without finishing the builder.
+  ///
+  /// Creates an internal temporary copy of current builder and finishes the copy.
+  /// Use this method, when the state of a long lasting builder need to be persisted periodically.
+  ByteBuffer snapshot() {
+    final tmp = Builder(size: _offset + 200);
+    tmp._offset = _offset;
+    tmp._stack = List.from(_stack);
+    tmp._stackPointers = List.from(_stackPointers);
+    tmp._buffer.buffer.asUint8List().setAll(0, _buffer.buffer.asUint8List(0, _offset));
+    for (var i = 0; i < tmp._stackPointers.length; i++){
+      tmp.end();
+    }
+    final buffer = tmp.finish();
+    final bd = ByteData(buffer.lengthInBytes);
+    bd.buffer.asUint8List().setAll(0, buffer);
+    return bd.buffer;
+  }
+  
+  void _integrityCheckOnValueAddition() {
+    if (_finished) {
+      throw StateError('Adding values after finish is prohibited');
+    }
+    if (_stackPointers.isNotEmpty && _stackPointers.last.isVector == false) {
+      if (_stack.last.type != ValueType.Key) {
+        throw StateError('Adding value to a map before adding a key is prohibited');
+      }
+    }
+  }
+
+  void _integrityCheckOnKeyAddition() {
+    if (_finished) {
+      throw StateError('Adding values after finish is prohibited');
+    }
+    if (_stackPointers.isEmpty || _stackPointers.last.isVector) {
+      throw StateError('Adding key before staring a map is prohibited');
+    }
+  }
+
+  void _finish() {
+    if (_stack.length != 1) {
+      throw StateError('Stack has to be exactly 1, but is ${_stack.length}. You have to end all started vectors and maps, before calling [finish]');
+    }
+    final value = _stack[0];
+    final byteWidth = _align(value.elementWidth(_offset, 0));
+    _writeStackValue(value, byteWidth);
+    _writeInt(value.storedPackedType(), 1);
+    _writeInt(byteWidth, 1);
+    _finished = true;
+  }
+  
+  _StackValue _createVector(int start, int vecLength, int step, [_StackValue keys]) {
+    var bitWidth = BitWidthUtil.width(vecLength);
+    var prefixElements = 1;
+    if (keys != null) {
+      var elemWidth = keys.elementWidth(_offset, 0);
+      if (elemWidth.index > bitWidth.index) {
+        bitWidth = elemWidth;
+      }
+      prefixElements += 2;
+    }
+    var vectorType = ValueType.Key;
+    var typed = keys == null;
+    for (var i = start; i < _stack.length; i += step) {
+      final elemWidth = _stack[i].elementWidth(_offset, i + prefixElements);
+      if (elemWidth.index > bitWidth.index) {
+        bitWidth = elemWidth;
+      }
+      if (i == start) {
+        vectorType = _stack[i].type;
+        typed &= ValueTypeUtils.isTypedVectorElement(vectorType);
+      } else {
+        if (vectorType != _stack[i].type) {
+          typed = false;
+        }
+      }
+    }
+    final byteWidth = _align(bitWidth);
+    final fix = typed & ValueTypeUtils.isNumber(vectorType) && vecLength >= 2 && vecLength <= 4;
+    if (keys != null) {
+      _writeStackValue(keys, byteWidth);
+      _writeInt(1 << keys.width.index, byteWidth);
+    }
+    if (fix == false) {
+      _writeInt(vecLength, byteWidth);
+    }
+    final vecOffset = _offset;
+    for (var i = start; i < _stack.length; i += step) {
+      _writeStackValue(_stack[i], byteWidth);
+    }
+    if (typed == false) {
+      for (var i = start; i < _stack.length; i += step) {
+        _writeInt(_stack[i].storedPackedType(), 1);
+      }
+    }
+    if (keys != null) {
+      return _StackValue.WithOffset(vecOffset, ValueType.Map, bitWidth);
+    }
+    if (typed) {
+      final vType = ValueTypeUtils.toTypedVector(vectorType, fix ? vecLength : 0);
+      return _StackValue.WithOffset(vecOffset, vType, bitWidth);
+    }
+    return _StackValue.WithOffset(vecOffset, ValueType.Vector, bitWidth);
+  }
+
+  void _endVector(_StackPointer pointer) {
+    final vecLength = _stack.length - pointer.stackPosition;
+    final vec = _createVector(pointer.stackPosition, vecLength, 1);
+    _stack.removeRange(pointer.stackPosition, _stack.length);
+    _stack.add(vec);
+  }
+
+  void _sortKeysAndEndMap(_StackPointer pointer) {
+    if (((_stack.length - pointer.stackPosition) & 1) == 1) {
+      throw StateError('The stack needs to hold key value pairs (even number of elements). Check if you combined [addKey] with add... method calls properly.');
+    }
+
+    var sorted = true;
+    for (var i = pointer.stackPosition; i < _stack.length - 2; i += 2) {
+      if (_shouldFlip(_stack[i], _stack[i+2])) {
+        sorted = false;
+        break;
+      }
+    }
+
+    if (sorted == false) {
+      for (var i = pointer.stackPosition; i < _stack.length; i += 2) {
+        var flipIndex = i;
+        for (var j = i + 2; j < _stack.length; j += 2) {
+          if (_shouldFlip(_stack[flipIndex], _stack[j])) {
+            flipIndex = j;
+          }
+        }
+        if (flipIndex != i) {
+          var k = _stack[flipIndex];
+          var v = _stack[flipIndex + 1];
+          _stack[flipIndex] = _stack[i];
+          _stack[flipIndex + 1] = _stack[i + 1];
+          _stack[i] = k;
+          _stack[i + 1] = v;
+        }
+      }
+    }
+    _endMap(pointer);
+  }
+  
+  void _endMap(_StackPointer pointer) {
+    final vecLength = (_stack.length - pointer.stackPosition) >> 1;
+    final offsets = <int>[];
+    for (var i = pointer.stackPosition; i < _stack.length; i += 2) {
+      offsets.add(_stack[i].offset);
+    }
+    final keysHash = _KeysHash(offsets);
+    var keysStackValue;
+    if (_keyVectorCache.containsKey(keysHash)) {
+      keysStackValue = _keyVectorCache[keysHash];
+    } else {
+      keysStackValue = _createVector(pointer.stackPosition, vecLength, 2);
+      _keyVectorCache[keysHash] = keysStackValue;
+    }
+    final vec = _createVector(pointer.stackPosition + 1, vecLength, 2, keysStackValue);
+    _stack.removeRange(pointer.stackPosition, _stack.length);
+    _stack.add(vec);
+  }
+
+  bool _shouldFlip(_StackValue v1, _StackValue v2) {
+    if (v1.type != ValueType.Key || v2.type != ValueType.Key) {
+      throw StateError('Stack values are not keys $v1 | $v2. Check if you combined [addKey] with add... method calls properly.');
+    }
+
+    var c1, c2;
+    var index = 0;
+    do {
+      c1 = _buffer.getUint8(v1.offset + index);
+      c2 = _buffer.getUint8(v2.offset + index);
+      if (c2 < c1) return true;
+      if (c1 < c2) return false;
+      index += 1;
+    } while (c1 != 0 && c2 != 0);
+    return false;
+  }
+
+  int _align(BitWidth width) {
+    final byteWidth = BitWidthUtil.toByteWidth(width);
+    _offset += BitWidthUtil.paddingSize(_offset, byteWidth);
+    return byteWidth;
+  }
+
+  void _writeStackValue(_StackValue value, int byteWidth) {
+    final newOffset = _newOffset(byteWidth);
+    if (value.isOffset) {
+      final relativeOffset = _offset - value.offset;
+      if (byteWidth == 8 || relativeOffset < (1 << (byteWidth * 8))) {
+        _writeInt(relativeOffset, byteWidth);
+      } else {
+        throw StateError('Unexpected size $byteWidth. This might be a bug. Please create an issue https://github.com/google/flatbuffers/issues/new');
+      }
+    } else {
+      _pushBuffer(value.asU8List(BitWidthUtil.fromByteWidth(byteWidth)));
+    }
+    _offset = newOffset;
+  }
+
+  void _writeInt(int value, int byteWidth) {
+    final newOffset = _newOffset(byteWidth);
+    _pushInt(value, BitWidthUtil.fromByteWidth(byteWidth));
+    _offset = newOffset;
+  }
+
+  int _newOffset(int newValueSize) {
+    final newOffset = _offset + newValueSize;
+    var size = _buffer.lengthInBytes;
+    final prevSize = size;
+    while (size < newOffset) {
+      size <<= 1;
+    }
+    if (prevSize < size) {
+      final newBuf = ByteData(size);
+      newBuf.buffer
+          .asUint8List()
+          .setAll(0, _buffer.buffer.asUint8List());
+    }
+    return newOffset;
+  }
+
+  void _pushInt(int value, BitWidth width) {
+    switch (width) {
+
+      case BitWidth.width8:
+        _buffer.setInt8(_offset, value);
+        break;
+      case BitWidth.width16:
+        _buffer.setInt16(_offset, value, Endian.little);
+        break;
+      case BitWidth.width32:
+        _buffer.setInt32(_offset, value, Endian.little);
+        break;
+      case BitWidth.width64:
+        _buffer.setInt64(_offset, value, Endian.little);
+        break;
+    }
+  }
+
+  void _pushBuffer(List<int> value) {
+    _buffer.buffer.asUint8List().setAll(_offset, value);
+  }
+}
+
+class _StackValue {
+  Object _value;
+  int _offset;
+  ValueType _type;
+  BitWidth _width;
+  _StackValue.WithNull() {
+    _type = ValueType.Null;
+    _width = BitWidth.width8;
+  }
+  _StackValue.WithInt(int value) {
+    _type = value != null ? ValueType.Int : ValueType.Null;
+    _width = BitWidthUtil.width(value);
+    _value = value;
+  }
+  _StackValue.WithBool(bool value) {
+    _type = value != null ? ValueType.Bool : ValueType.Null;
+    _width = BitWidth.width8;
+    _value = value;
+  }
+  _StackValue.WithDouble(double value) {
+    _type = value != null ? ValueType.Float : ValueType.Null;
+    _width = BitWidthUtil.width(value);
+    _value = value;
+  }
+  _StackValue.WithOffset(int value, ValueType type, BitWidth width) {
+    _offset = value;
+    _type = type;
+    _width = width;
+  }
+
+  BitWidth storedWidth({BitWidth width = BitWidth.width8}) {
+    return ValueTypeUtils.isInline(_type) ? BitWidthUtil.max(_width, width) : _width;
+  }
+
+  int storedPackedType({BitWidth width = BitWidth.width8}) {
+    return ValueTypeUtils.packedType(_type, storedWidth(width: width));
+  }
+
+  BitWidth elementWidth(int size, int index) {
+    if (ValueTypeUtils.isInline(_type)) return _width;
+    for(var i = 0; i < 4; i++) {
+      final width = 1 << i;
+      final offsetLoc = size + BitWidthUtil.paddingSize(size, width) + index * width;
+      final offset = offsetLoc - _offset;
+      final bitWidth = BitWidthUtil.width(offset);
+      if (1 << bitWidth.index == width) {
+        return bitWidth;
+      }
+    }
+    throw StateError('Element is of unknown. Size: $size at index: $index. This might be a bug. Please create an issue https://github.com/google/flatbuffers/issues/new');
+  }
+
+  List<int> asU8List(BitWidth width) {
+    if (ValueTypeUtils.isNumber(_type)) {
+      if (_type == ValueType.Float) {
+        if (width == BitWidth.width32) {
+          final result = ByteData(4);
+          result.setFloat32(0, _value, Endian.little);
+          return result.buffer.asUint8List();
+        } else {
+          final result = ByteData(8);
+          result.setFloat64(0, _value, Endian.little);
+          return result.buffer.asUint8List();
+        }
+      } else {
+        switch(width) {
+          case BitWidth.width8:
+            final result = ByteData(1);
+            result.setInt8(0, _value);
+            return result.buffer.asUint8List();
+          case BitWidth.width16:
+            final result = ByteData(2);
+            result.setInt16(0, _value, Endian.little);
+            return result.buffer.asUint8List();
+          case BitWidth.width32:
+            final result = ByteData(4);
+            result.setInt32(0, _value, Endian.little);
+            return result.buffer.asUint8List();
+          case BitWidth.width64:
+            final result = ByteData(8);
+            result.setInt64(0, _value, Endian.little);
+            return result.buffer.asUint8List();
+        }
+      }
+    }
+    if (_type == ValueType.Null) {
+      final result = ByteData(1);
+      result.setInt8(0, 0);
+      return result.buffer.asUint8List();
+    }
+    if (_type == ValueType.Bool) {
+      final result = ByteData(1);
+      result.setInt8(0, _value ? 1 : 0);
+      return result.buffer.asUint8List();
+    }
+
+    throw StateError('Unexpected type: $_type. This might be a bug. Please create an issue https://github.com/google/flatbuffers/issues/new');
+  }
+
+  ValueType get type {
+    return _type;
+  }
+
+  BitWidth get width {
+    return _width;
+  }
+
+  bool get isOffset {
+    return !ValueTypeUtils.isInline(_type);
+  }
+  int get offset => _offset;
+
+  bool get isFloat32 {
+    return _type == ValueType.Float && _width == BitWidth.width32;
+  }
+}
+
+class _StackPointer {
+  int stackPosition;
+  bool isVector;
+  _StackPointer(this.stackPosition, this.isVector);
+}
+
+class _KeysHash {
+  final List<int> keys;
+
+  const _KeysHash(this.keys);
+
+  @override
+  bool operator ==(Object other) {
+    if (other is _KeysHash) {
+      if (keys.length != other.keys.length) return false;
+      for (var i = 0; i < keys.length; i++) {
+        if (keys[i] != other.keys[i]) return false;
+      }
+      return true;
+    }
+    return false;
+  }
+
+  @override
+  int get hashCode {
+    var result = 17;
+    for (var i = 0; i < keys.length; i++) {
+      result = result * 23 + keys[i];
+    }
+    return result;
+  }
+}

dart/lib/src/reference.dart

@@ -0,0 +1,446 @@
+import 'dart:collection';
+import 'dart:convert';
+import 'dart:typed_data';
+import 'types.dart';
+
+/// Main class to read a value out of a FlexBuffer.
+///
+/// This class let you access values stored in the buffer in a lazy fashion.
+class Reference {
+  final ByteData _buffer;
+  final int _offset;
+  final BitWidth _parentWidth;
+  final String _path;
+  int _byteWidth;
+  ValueType _valueType;
+  int _length;
+
+  Reference._(this._buffer, this._offset, this._parentWidth, int packedType, this._path) {
+    _byteWidth = 1 << (packedType & 3);
+    _valueType = ValueTypeUtils.fromInt(packedType >> 2);
+  }
+
+  /// Use this method to access the root value of a FlexBuffer.
+  static Reference fromBuffer(ByteBuffer buffer) {
+    final len = buffer.lengthInBytes;
+    if (len < 3) {
+      throw UnsupportedError('Buffer needs to be bigger than 3');
+    }
+    final byteData = ByteData.view(buffer);
+    final byteWidth = byteData.getUint8(len - 1);
+    final packedType = byteData.getUint8(len - 2);
+    final offset = len - byteWidth - 2;
+    return Reference._(ByteData.view(buffer), offset, BitWidthUtil.fromByteWidth(byteWidth), packedType, "/");
+  }
+
+  /// Returns true if the underlying value is null.
+  bool get isNull => _valueType == ValueType.Null;
+  /// Returns true if the underlying value can be represented as [num].
+  bool get isNum => ValueTypeUtils.isNumber(_valueType) || ValueTypeUtils.isIndirectNumber(_valueType);
+  /// Returns true if the underlying value was encoded as a float (direct or indirect).
+  bool get isDouble => _valueType == ValueType.Float || _valueType == ValueType.IndirectFloat;
+  /// Returns true if the underlying value was encoded as an int or uint (direct or indirect).
+  bool get isInt => isNum && !isDouble;
+  /// Returns true if the underlying value was encoded as a string or a key.
+  bool get isString => _valueType == ValueType.String || _valueType == ValueType.Key;
+  /// Returns true if the underlying value was encoded as a bool.
+  bool get isBool => _valueType == ValueType.Bool;
+  /// Returns true if the underlying value was encoded as a blob.
+  bool get isBlob => _valueType == ValueType.Blob;
+  /// Returns true if the underlying value points to a vector.
+  bool get isVector => ValueTypeUtils.isAVector(_valueType);
+  /// Returns true if the underlying value points to a map.
+  bool get isMap => _valueType == ValueType.Map;
+
+  /// If this [isBool], returns the bool value. Otherwise, returns null.
+  bool get boolValue {
+    if(_valueType == ValueType.Bool) {
+      return _readInt(_offset, _parentWidth) != 0;
+    }
+    return null;
+  }
+
+  /// Returns an [int], if the underlying value can be represented as an int.
+  ///
+  /// Otherwise returns [null].
+  int get intValue {
+    if (_valueType == ValueType.Int) {
+      return _readInt(_offset, _parentWidth);
+    }
+    if (_valueType == ValueType.UInt) {
+      return _readUInt(_offset, _parentWidth);
+    }
+    if (_valueType == ValueType.IndirectInt) {
+      return _readInt(_indirect, BitWidthUtil.fromByteWidth(_byteWidth));
+    }
+    if (_valueType == ValueType.IndirectUInt) {
+      return _readUInt(_indirect, BitWidthUtil.fromByteWidth(_byteWidth));
+    }
+    return null;
+  }
+
+  /// Returns [double], if the underlying value [isDouble].
+  ///
+  /// Otherwise returns [null].
+  double get doubleValue {
+    if (_valueType == ValueType.Float) {
+      return _readFloat(_offset, _parentWidth);
+    }
+    if (_valueType == ValueType.IndirectFloat) {
+      return _readFloat(_indirect, BitWidthUtil.fromByteWidth(_byteWidth));
+    }
+    return null;
+  }
+
+  /// Returns [num], if the underlying value is numeric, be it int uint, or float (direct or indirect).
+  ///
+  /// Otherwise returns [null].
+  num get numValue => doubleValue ?? intValue;
+
+  /// Returns [String] value or null otherwise.
+  /// 
+  /// This method performers a utf8 decoding, as FlexBuffers format stores strings in utf8 encoding. 
+  String get stringValue {
+    if (_valueType == ValueType.String || _valueType == ValueType.Key) {
+      return utf8.decode(_buffer.buffer.asUint8List(_indirect, length));
+    }
+    return null;
+  }
+
+  /// Returns [Uint8List] value or null otherwise.
+  Uint8List get blobValue {
+    if (_valueType == ValueType.Blob) {
+      return _buffer.buffer.asUint8List(_indirect, length);
+    }
+    return null;
+  }
+
+  /// Can be used with an [int] or a [String] value for key.
+  /// If the underlying value in FlexBuffer is a vector, then use [int] for access.
+  /// If the underlying value in FlexBuffer is a map, then use [String] for access.
+  /// Returns [Reference] value. Throws an exception when [key] is not applicable.
+  Reference operator [](Object key) {
+    if (key is int && ValueTypeUtils.isAVector(_valueType)) {
+      final index = key;
+      if(index >= length || index < 0) {
+        throw ArgumentError('Key: [$key] is not applicable on: $_path of: $_valueType length: $length');
+      }
+      final elementOffset = _indirect + index * _byteWidth;
+      final reference = Reference._(_buffer, elementOffset, BitWidthUtil.fromByteWidth(_byteWidth), 0, "$_path[$index]");
+      reference._byteWidth = 1;
+      if (ValueTypeUtils.isTypedVector(_valueType)) {
+        reference._valueType = ValueTypeUtils.typedVectorElementType(_valueType);
+        return reference;
+      }
+      if(ValueTypeUtils.isFixedTypedVector(_valueType)) {
+        reference._valueType = ValueTypeUtils.fixedTypedVectorElementType(_valueType);
+        return reference;
+      }
+      final packedType = _buffer.getUint8(_indirect + length * _byteWidth + index);
+      return Reference._(_buffer, elementOffset, BitWidthUtil.fromByteWidth(_byteWidth), packedType, "$_path[$index]");
+    }
+    if (key is String && _valueType == ValueType.Map) {
+      final index = _keyIndex(key);
+      if (index != null) {
+        return _valueForIndexWithKey(index, key);
+      }
+    }
+    throw ArgumentError('Key: [$key] is not applicable on: $_path of: $_valueType');
+  }
+
+  /// Get an iterable if the underlying flexBuffer value is a vector.
+  /// Otherwise throws an exception.
+  Iterable<Reference> get vectorIterable {
+    if(isVector == false) {
+      throw UnsupportedError('Value is not a vector. It is: $_valueType');
+    }
+    return _VectorIterator(this);
+  }
+
+  /// Get an iterable for keys if the underlying flexBuffer value is a map.
+  /// Otherwise throws an exception.
+  Iterable<String> get mapKeyIterable {
+    if(isMap == false) {
+      throw UnsupportedError('Value is not a map. It is: $_valueType');
+    }
+    return _MapKeyIterator(this);
+  }
+
+  /// Get an iterable for values if the underlying flexBuffer value is a map.
+  /// Otherwise throws an exception.
+  Iterable<Reference> get mapValueIterable {
+    if(isMap == false) {
+      throw UnsupportedError('Value is not a map. It is: $_valueType');
+    }
+    return _MapValueIterator(this);
+  }
+
+  /// Returns the length of the the underlying FlexBuffer value.
+  /// If the underlying value is [null] the length is 0.
+  /// If the underlying value is a number, or a bool, the length is 1.
+  /// If the underlying value is a vector, or map, the length reflects number of elements / element pairs.
+  /// If the values is a string or a blob, the length reflects a number of bytes the value occupies (strings are encoded in utf8 format).
+  int get length {
+    if (_length != null) {
+      return _length;
+    }
+    // needs to be checked before more generic isAVector
+    if(ValueTypeUtils.isFixedTypedVector(_valueType)) {
+      _length = ValueTypeUtils.fixedTypedVectorElementSize(_valueType);
+    } else if(_valueType == ValueType.Blob || ValueTypeUtils.isAVector(_valueType) || _valueType == ValueType.Map){
+      _length = _readInt(_indirect - _byteWidth, BitWidthUtil.fromByteWidth(_byteWidth));
+    } else if (_valueType == ValueType.Null) {
+      _length = 0;
+    } else if (_valueType == ValueType.String) {
+      final indirect = _indirect;
+      var size_byte_width = _byteWidth;
+      var size = _readInt(indirect - size_byte_width, BitWidthUtil.fromByteWidth(size_byte_width));
+      while (_buffer.getInt8(indirect + size) != 0) {
+        size_byte_width <<= 1;
+        size = _readInt(indirect - size_byte_width, BitWidthUtil.fromByteWidth(size_byte_width));
+      }
+      _length = size;
+    } else if (_valueType == ValueType.Key) {
+      final indirect = _indirect;
+      var size = 1;
+      while (_buffer.getInt8(indirect + size) != 0) {
+        size += 1;
+      }
+      _length = size;
+    } else {
+      _length = 1;
+    }
+    return _length;
+  }
+
+
+  /// Returns a minified JSON representation of the underlying FlexBuffer value.
+  ///
+  /// This method involves materializing the entire object tree, which may be
+  /// expensive. It is more efficient to work with [Reference] and access only the needed data.
+  /// Blob values are represented as base64 encoded string.
+  String get json {
+    if(_valueType == ValueType.Bool) {
+      return boolValue ? 'true' : 'false';
+    }
+    if (_valueType == ValueType.Null) {
+      return 'null';
+    }
+    if(ValueTypeUtils.isNumber(_valueType)) {
+      return jsonEncode(numValue);
+    }
+    if (_valueType == ValueType.String) {
+      return jsonEncode(stringValue);
+    }
+    if (_valueType == ValueType.Blob) {
+      return jsonEncode(base64Encode(blobValue));
+    }
+    if (ValueTypeUtils.isAVector(_valueType)) {
+      final result = StringBuffer();
+      result.write('[');
+      for (var i = 0; i < length; i++) {
+        result.write(this[i].json);
+        if (i < length - 1) {
+          result.write(',');
+        }
+      }
+      result.write(']');
+      return result.toString();
+    }
+    if (_valueType == ValueType.Map) {
+      final result = StringBuffer();
+      result.write('{');
+      for (var i = 0; i < length; i++) {
+        result.write(jsonEncode(_keyForIndex(i)));
+        result.write(':');
+        result.write(_valueForIndex(i).json);
+        if (i < length - 1) {
+          result.write(',');
+        }
+      }
+      result.write('}');
+      return result.toString();
+    }
+    throw UnsupportedError('Type: $_valueType is not supported for JSON conversion');
+  }
+
+  /// Computes the indirect offset of the value.
+  ///
+  /// To optimize for the more common case of being called only once, this
+  /// value is not cached. Callers that need to use it more than once should
+  /// cache the return value in a local variable.
+  int get _indirect {
+    final step = _readInt(_offset, _parentWidth);
+    return _offset - step;
+  }
+
+  int _readInt(int offset, BitWidth width) {
+    _validateOffset(offset, width);
+    if (width == BitWidth.width8) {
+      return _buffer.getInt8(offset);
+    }
+    if (width == BitWidth.width16) {
+      return _buffer.getInt16(offset, Endian.little);
+    }
+    if (width == BitWidth.width32) {
+      return _buffer.getInt32(offset, Endian.little);
+    }
+    return _buffer.getInt64(offset, Endian.little);
+  }
+
+  int _readUInt(int offset, BitWidth width) {
+    _validateOffset(offset, width);
+    if (width == BitWidth.width8) {
+      return _buffer.getUint8(offset);
+    }
+    if (width == BitWidth.width16) {
+      return _buffer.getUint16(offset, Endian.little);
+    }
+    if (width == BitWidth.width32) {
+      return _buffer.getUint32(offset, Endian.little);
+    }
+    return _buffer.getUint64(offset, Endian.little);
+  }
+
+  double _readFloat(int offset, BitWidth width) {
+    _validateOffset(offset, width);
+    if (width.index < BitWidth.width32.index) {
+      throw StateError('Bad width: $width');
+    }
+
+    if (width == BitWidth.width32) {
+      return _buffer.getFloat32(offset, Endian.little);
+    }
+
+    return _buffer.getFloat64(offset, Endian.little);
+  }
+
+  void _validateOffset(int offset, BitWidth width) {
+    if (_offset < 0 || _buffer.lengthInBytes <= offset + width.index || offset & (BitWidthUtil.toByteWidth(width) - 1) != 0) {
+      throw StateError('Bad offset: $offset, width: $width');
+    }
+  }
+
+  int _keyIndex(String key) {
+    final input = utf8.encode(key);
+    final keysVectorOffset = _indirect - _byteWidth * 3;
+    final indirectOffset = keysVectorOffset - _readInt(keysVectorOffset, BitWidthUtil.fromByteWidth(_byteWidth));
+    final byteWidth = _readInt(keysVectorOffset + _byteWidth, BitWidthUtil.fromByteWidth(_byteWidth));
+    var low = 0;
+    var high = length - 1;
+    while (low <= high) {
+      final mid = (high + low) >> 1;
+      final dif = _diffKeys(input, mid, indirectOffset, byteWidth);
+      if (dif == 0) return mid;
+      if (dif < 0) {
+        high = mid - 1;
+      } else {
+        low = mid + 1;
+      }
+    }
+    return null;
+  }
+
+  int _diffKeys(List<int> input, int index, int indirect_offset, int byteWidth) {
+    final keyOffset = indirect_offset + index * byteWidth;
+    final keyIndirectOffset = keyOffset - _readInt(keyOffset, BitWidthUtil.fromByteWidth(byteWidth));
+    for (var i = 0; i < input.length; i++) {
+      final dif = input[i] - _buffer.getUint8(keyIndirectOffset + i);
+      if (dif != 0) {
+        return dif;
+      }
+    }
+    return (_buffer.getUint8(keyIndirectOffset + input.length) == 0) ? 0 : -1;
+  }
+
+  Reference _valueForIndexWithKey(int index, String key) {
+    final indirect = _indirect;
+    final elementOffset = indirect + index * _byteWidth;
+    final packedType = _buffer.getUint8(indirect + length * _byteWidth + index);
+    return Reference._(_buffer, elementOffset, BitWidthUtil.fromByteWidth(_byteWidth), packedType, "$_path/$key");
+  }
+
+  Reference _valueForIndex(int index) {
+    final indirect = _indirect;
+    final elementOffset = indirect + index * _byteWidth;
+    final packedType = _buffer.getUint8(indirect + length * _byteWidth + index);
+    return Reference._(_buffer, elementOffset, BitWidthUtil.fromByteWidth(_byteWidth), packedType, "$_path/[$index]");
+  }
+
+  String _keyForIndex(int index) {
+    final keysVectorOffset = _indirect - _byteWidth * 3;
+    final indirectOffset = keysVectorOffset - _readInt(keysVectorOffset, BitWidthUtil.fromByteWidth(_byteWidth));
+    final byteWidth = _readInt(keysVectorOffset + _byteWidth, BitWidthUtil.fromByteWidth(_byteWidth));
+    final keyOffset = indirectOffset + index * byteWidth;
+    final keyIndirectOffset = keyOffset - _readInt(keyOffset, BitWidthUtil.fromByteWidth(byteWidth));
+    var length = 0;
+    while (_buffer.getUint8(keyIndirectOffset + length) != 0) {
+      length += 1;
+    }
+    return utf8.decode(_buffer.buffer.asUint8List(keyIndirectOffset, length));
+  }
+
+}
+
+class _VectorIterator with IterableMixin<Reference> implements Iterator<Reference> {
+  final Reference _vector;
+  int index;
+
+  _VectorIterator(this._vector) {
+    index = -1;
+  }
+
+  @override
+  Reference get current => _vector[index];
+
+  @override
+  bool moveNext() {
+    index++;
+    return index < _vector.length;
+  }
+
+  @override
+  Iterator<Reference> get iterator => this;
+}
+
+class _MapKeyIterator with IterableMixin<String> implements Iterator<String> {
+  final Reference _map;
+  int index;
+
+  _MapKeyIterator(this._map) {
+    index = -1;
+  }
+
+  @override
+  String get current => _map._keyForIndex(index);
+
+  @override
+  bool moveNext() {
+    index++;
+    return index < _map.length;
+  }
+
+  @override
+  Iterator<String> get iterator => this;
+}
+
+class _MapValueIterator with IterableMixin<Reference> implements Iterator<Reference> {
+  final Reference _map;
+  int index;
+
+  _MapValueIterator(this._map) {
+    index = -1;
+  }
+
+  @override
+  Reference get current => _map._valueForIndex(index);
+
+  @override
+  bool moveNext() {
+    index++;
+    return index < _map.length;
+  }
+
+  @override
+  Iterator<Reference> get iterator => this;
+}

dart/lib/src/types.dart

@@ -0,0 +1,156 @@
+import 'dart:typed_data';
+
+/// Represents the number of bits a value occupies.
+enum BitWidth {
+  width8,
+  width16,
+  width32,
+  width64
+}
+
+class BitWidthUtil {
+  static int toByteWidth(BitWidth self) {
+    return 1 << self.index;
+  }
+  static BitWidth width(num value) {
+    if (value.toInt() == value) {
+      var v = value.toInt().abs();
+      if (v >> 7 == 0) return BitWidth.width8;
+      if (v >> 15 == 0) return BitWidth.width16;
+      if (v >> 31 == 0) return BitWidth.width32;
+      return BitWidth.width64;
+    }
+    return value == _toF32(value) ? BitWidth.width32 : BitWidth.width64;
+  }
+  static BitWidth fromByteWidth(int value) {
+    if (value == 1) {
+      return BitWidth.width8;
+    }
+    if (value == 2) {
+      return BitWidth.width16;
+    }
+    if (value == 4) {
+      return BitWidth.width32;
+    }
+    if (value == 8) {
+      return BitWidth.width64;
+    }
+    throw Exception('Unexpected value ${value}');
+  }
+  static int paddingSize(int bufSize, int scalarSize) {
+    return (~bufSize + 1) & (scalarSize - 1);
+  }
+  static double _toF32(double value) {
+    var bdata = ByteData(4);
+    bdata.setFloat32(0, value);
+    return bdata.getFloat32(0);
+  }
+
+  static BitWidth max(BitWidth self, BitWidth other) {
+    if (self.index < other.index) {
+      return other;
+    }
+    return self;
+  }
+}
+
+/// Represents all internal FlexBuffer types.
+enum ValueType {
+  Null, Int, UInt, Float,
+  Key, String, IndirectInt, IndirectUInt, IndirectFloat,
+  Map, Vector, VectorInt, VectorUInt, VectorFloat, VectorKey,
+  @Deprecated('VectorString is deprecated due to a flaw in the binary format (https://github.com/google/flatbuffers/issues/5627)')
+  VectorString,
+  VectorInt2, VectorUInt2, VectorFloat2,
+  VectorInt3, VectorUInt3, VectorFloat3,
+  VectorInt4, VectorUInt4, VectorFloat4,
+  Blob, Bool, VectorBool
+}
+
+class ValueTypeUtils {
+  static int toInt(ValueType self) {
+    if (self == ValueType.VectorBool) return 36;
+    return self.index;
+  }
+
+  static ValueType fromInt(int value) {
+    if (value == 36) return ValueType.VectorBool;
+    return ValueType.values[value];
+  }
+
+  static bool isInline(ValueType self) {
+    return self == ValueType.Bool
+        || toInt(self) <= toInt(ValueType.Float);
+  }
+
+  static bool isNumber(ValueType self) {
+    return toInt(self) >= toInt(ValueType.Int)
+        && toInt(self) <= toInt(ValueType.Float);
+  }
+
+  static bool isIndirectNumber(ValueType self) {
+    return toInt(self) >= toInt(ValueType.IndirectInt)
+        && toInt(self) <= toInt(ValueType.IndirectFloat);
+  }
+
+  static bool isTypedVectorElement(ValueType self) {
+    return self == ValueType.Bool ||
+        (
+            toInt(self) >= toInt(ValueType.Int)
+            && toInt(self) <= toInt(ValueType.String)
+        );
+  }
+
+  static bool isTypedVector(ValueType self) {
+    return self == ValueType.VectorBool ||
+        (
+          toInt(self) >= toInt(ValueType.VectorInt)
+              && toInt(self) <= toInt(ValueType.VectorString)
+        );
+  }
+
+  static bool isFixedTypedVector(ValueType self) {
+    return (
+            toInt(self) >= toInt(ValueType.VectorInt2)
+                && toInt(self) <= toInt(ValueType.VectorFloat4)
+        );
+  }
+
+  static bool isAVector(ValueType self) {
+    return (
+        isTypedVector(self) || isFixedTypedVector(self) || self == ValueType.Vector
+    );
+  }
+
+  static ValueType toTypedVector(ValueType self, int length) {
+    if (length == 0) {
+      return ValueTypeUtils.fromInt(toInt(self) - toInt(ValueType.Int) + toInt(ValueType.VectorInt));
+    }
+    if (length == 2) {
+      return ValueTypeUtils.fromInt(toInt(self) - toInt(ValueType.Int) + toInt(ValueType.VectorInt2));
+    }
+    if (length == 3) {
+      return ValueTypeUtils.fromInt(toInt(self) - toInt(ValueType.Int) + toInt(ValueType.VectorInt3));
+    }
+    if (length == 4) {
+      return ValueTypeUtils.fromInt(toInt(self) - toInt(ValueType.Int) + toInt(ValueType.VectorInt4));
+    }
+    throw Exception('unexpected length ' + length.toString());
+  }
+
+  static ValueType typedVectorElementType(ValueType self) {
+    return ValueTypeUtils.fromInt(toInt(self) - toInt(ValueType.VectorInt) + toInt(ValueType.Int));
+  }
+
+  static ValueType fixedTypedVectorElementType(ValueType self) {
+    return ValueTypeUtils.fromInt((toInt(self) - toInt(ValueType.VectorInt2)) % 3 + toInt(ValueType.Int));
+  }
+
+  static int fixedTypedVectorElementSize(ValueType self) {
+    return (toInt(self) - toInt(ValueType.VectorInt2)) ~/ 3 + 2;
+  }
+
+  static int packedType(ValueType self, BitWidth bitWidth) {
+    return bitWidth.index | (toInt(self) << 2);
+  }
+}

dart/test/flex_builder_test.dart

@@ -0,0 +1,315 @@
+import 'dart:typed_data';
+
+import 'package:flat_buffers/flex_buffers.dart' show Builder;
+import 'package:test/test.dart';
+
+void main() {
+  test('build with single value', () {
+    {
+      var flx = Builder();
+      flx.addNull();
+      expect(flx.finish(), [0, 0, 1]);
+    }
+    {
+      var flx = Builder();
+      flx.addBool(true);
+      expect(flx.finish(), [1, 104, 1]);
+    }
+    {
+      var flx = Builder();
+      flx.addBool(false);
+      expect(flx.finish(), [0, 104, 1]);
+    }
+    {
+      var flx = Builder();
+      flx.addInt(1);
+      expect(flx.finish(), [1, 4, 1]);
+    }
+    {
+      var flx = Builder();
+      flx.addInt(230);
+      expect(flx.finish(), [230, 0, 5, 2]);
+    }
+    {
+      var flx = Builder();
+      flx.addInt(1025);
+      expect(flx.finish(), [1, 4, 5, 2]);
+    }
+    {
+      var flx = Builder();
+      flx.addInt(-1025);
+      expect(flx.finish(), [255, 251, 5, 2]);
+    }
+    {
+      var flx = Builder();
+      flx.addDouble(0.1);
+      expect(flx.finish(), [154, 153, 153, 153, 153, 153, 185, 63, 15, 8]);
+    }
+    {
+      var flx = Builder();
+      flx.addDouble(0.5);
+      expect(flx.finish(), [0, 0, 0, 63, 14, 4]);
+    }
+    {
+      var flx = Builder();
+      flx.addString('Maxim');
+      expect(flx.finish(), [5, 77, 97, 120, 105, 109, 0, 6, 20, 1]);
+    }
+    {
+      var flx = Builder();
+      flx.addString('hello 😱');
+      expect(flx.finish(), [10, 104, 101, 108, 108, 111, 32, 240, 159, 152, 177, 0, 11, 20, 1]);
+    }
+  });
+
+  test('build vector', (){
+    {
+      var flx = Builder()
+        ..startVector()
+        ..addInt(1)
+        ..addInt(2)
+        ..end()
+      ;
+      expect(flx.finish(), [1, 2, 2, 64, 1]);
+    }
+    {
+      var flx = Builder()
+        ..startVector()
+        ..addInt(-1)
+        ..addInt(256)
+        ..end()
+      ;
+      expect(flx.finish(), [255, 255, 0, 1, 4, 65, 1]);
+    }
+    {
+      var flx = Builder()
+        ..startVector()
+        ..addInt(-45)
+        ..addInt(256000)
+        ..end()
+      ;
+      expect(flx.finish(), [211, 255, 255, 255, 0, 232, 3, 0, 8, 66, 1]);
+    }
+    {
+      var flx = Builder()
+        ..startVector()
+        ..addDouble(1.1)
+        ..addDouble(-256)
+        ..end()
+      ;
+      expect(flx.finish(), [154, 153, 153, 153, 153, 153, 241, 63, 0, 0, 0, 0, 0, 0, 112, 192, 16, 75, 1]);
+    }
+    {
+      var flx = Builder()
+        ..startVector()
+        ..addInt(1)
+        ..addInt(2)
+        ..addInt(4)
+        ..end()
+      ;
+      expect(flx.finish(), [1, 2, 4, 3, 76, 1]);
+    }
+    {
+      var flx = Builder()
+        ..startVector()
+        ..addInt(-1)
+        ..addInt(256)
+        ..addInt(4)
+        ..end()
+      ;
+      expect(flx.finish(), [255, 255, 0, 1, 4, 0, 6, 77, 1]);
+    }
+    {
+      var flx = Builder()
+        ..startVector()
+          ..startVector()
+          ..addInt(61)
+          ..end()
+        ..addInt(64)
+        ..end()
+      ;
+      expect(flx.finish(), [1, 61, 2, 2, 64, 44, 4, 4, 40, 1]);
+    }
+    {
+      var flx = Builder()
+        ..startVector()
+        ..addString('foo')
+        ..addString('bar')
+        ..addString('baz')
+        ..end()
+      ;
+      expect(flx.finish(), [3, 102, 111, 111, 0, 3, 98, 97, 114, 0, 3, 98, 97, 122, 0, 3, 15, 11, 7, 3, 60, 1]);
+    }
+    {
+      var flx = Builder()
+        ..startVector()
+        ..addString('foo')
+        ..addString('bar')
+        ..addString('baz')
+        ..addString('foo')
+        ..addString('bar')
+        ..addString('baz')
+        ..end()
+      ;
+      expect(flx.finish(), [3, 102, 111, 111, 0, 3, 98, 97, 114, 0, 3, 98, 97, 122, 0, 6, 15, 11, 7, 18, 14, 10, 6, 60, 1]);
+    }
+    {
+      var flx = Builder()
+        ..startVector()
+        ..addBool(true)
+        ..addBool(false)
+        ..addBool(true)
+        ..end()
+      ;
+      expect(flx.finish(), [3, 1, 0, 1, 3, 144, 1]);
+    }
+    {
+      var flx = Builder()
+        ..startVector()
+        ..addString('foo')
+        ..addInt(1)
+        ..addInt(-5)
+        ..addDouble(1.3)
+        ..addBool(true)
+        ..end()
+      ;
+      expect(flx.finish(), [
+        3, 102, 111, 111, 0, 0, 0, 0,
+        5, 0, 0, 0, 0, 0, 0, 0,
+        15, 0, 0, 0, 0, 0, 0, 0,
+        1, 0, 0, 0, 0, 0, 0, 0,
+        251, 255, 255, 255, 255, 255, 255, 255,
+        205, 204, 204, 204, 204, 204, 244, 63,
+        1, 0, 0, 0, 0, 0, 0, 0,
+        20, 4, 4, 15, 104, 45, 43, 1]);
+    }
+  });
+
+  test('build map', ()
+  {
+    {
+      var flx = Builder()
+        ..startMap()
+        ..addKey('a')
+        ..addInt(12)
+        ..end()
+      ;
+      expect(flx.finish(), [97, 0, 1, 3, 1, 1, 1, 12, 4, 2, 36, 1]);
+    }
+    {
+      var flx = Builder()
+        ..startMap()
+        ..addKey('a')
+        ..addInt(12)
+        ..addKey('')
+        ..addInt(45)
+        ..end()
+      ;
+      expect(flx.finish(), [97, 0, 0, 2, 2, 5, 2, 1, 2, 45, 12, 4, 4, 4, 36, 1]);
+    }
+    {
+      var flx = Builder()
+        ..startVector()
+          ..startMap()
+            ..addKey('something')
+            ..addInt(12)
+          ..end()
+          ..startMap()
+            ..addKey('something')
+            ..addInt(45)
+          ..end()
+        ..end()
+      ;
+      expect(flx.finish(), [115, 111, 109, 101, 116, 104, 105, 110, 103, 0,
+        1, 11, 1, 1, 1, 12, 4, 6, 1, 1, 45, 4, 2, 8, 4, 36, 36, 4, 40, 1]);
+    }
+  });
+
+  test('build blob', ()
+  {
+    {
+      var flx = Builder()
+        ..addBlob(Uint8List.fromList([1, 2, 3]).buffer)
+      ;
+      expect(flx.finish(), [3, 1, 2, 3, 3, 100, 1]);
+    }
+  });
+
+  test('build from object', (){
+    expect(Builder.buildFromObject(Uint8List.fromList([1, 2, 3]).buffer).asUint8List(), [3, 1, 2, 3, 3, 100, 1]);
+    expect(Builder.buildFromObject(null).asUint8List(), [0, 0, 1]);
+    expect(Builder.buildFromObject(true).asUint8List(), [1, 104, 1]);
+    expect(Builder.buildFromObject(false).asUint8List(), [0, 104, 1]);
+    expect(Builder.buildFromObject(25).asUint8List(), [25, 4, 1]);
+    expect(Builder.buildFromObject(-250).asUint8List(), [6, 255, 5, 2]);
+    expect(Builder.buildFromObject(-2.50).asUint8List(), [0, 0, 32, 192, 14, 4]);
+    expect(Builder.buildFromObject('Maxim').asUint8List(), [5, 77, 97, 120, 105, 109, 0, 6, 20, 1]);
+    expect(Builder.buildFromObject([1, 3.3, 'max', true, null, false]).asUint8List(), [
+      3, 109, 97, 120, 0, 0, 0, 0,
+      6, 0, 0, 0, 0, 0, 0, 0,
+      1, 0, 0, 0, 0, 0, 0, 0,
+      102, 102, 102, 102, 102, 102, 10, 64,
+      31, 0, 0, 0, 0, 0, 0, 0,
+      1, 0, 0, 0, 0, 0, 0, 0,
+      0, 0, 0, 0, 0, 0, 0, 0,
+      0, 0, 0, 0, 0, 0, 0, 0,
+      4, 15, 20, 104, 0, 104, 54, 43, 1
+    ]);
+    expect(Builder.buildFromObject([{'something':12}, {'something': 45}]).asUint8List(), [
+      115, 111, 109, 101, 116, 104, 105, 110, 103, 0,
+      1, 11, 1, 1, 1, 12, 4, 6, 1, 1, 45, 4, 2, 8, 4, 36, 36, 4, 40, 1
+    ]);
+  });
+
+  test('add double indirectly', (){
+    var flx = Builder()
+      ..addDoubleIndirectly(0.1)
+    ;
+    expect(flx.finish(), [154, 153, 153, 153, 153, 153, 185, 63, 8, 35, 1]);
+  });
+
+  test('add double indirectly to vector with cache', (){
+    var flx = Builder()
+      ..startVector()
+      ..addDoubleIndirectly(0.1, cache: true)
+      ..addDoubleIndirectly(0.1, cache: true)
+      ..addDoubleIndirectly(0.1, cache: true)
+      ..addDoubleIndirectly(0.1, cache: true)
+      ..end()
+    ;
+    expect(flx.finish(), [154, 153, 153, 153, 153, 153, 185, 63,
+      4, 9, 10, 11, 12, 35, 35, 35, 35, 8, 40, 1]);
+  });
+
+  test('add int indirectly', (){
+    var flx = Builder()
+      ..addIntIndirectly(2345234523452345)
+    ;
+    expect(flx.finish(), [185, 115, 175, 118, 250, 84, 8, 0, 8, 27, 1]);
+  });
+
+  test('add int indirectly to vector with cache', (){
+    var flx = Builder()
+      ..startVector()
+      ..addIntIndirectly(2345234523452345, cache: true)
+      ..addIntIndirectly(2345234523452345, cache: true)
+      ..addIntIndirectly(2345234523452345, cache: true)
+      ..addIntIndirectly(2345234523452345, cache: true)
+      ..end()
+    ;
+    expect(flx.finish(), [185, 115, 175, 118, 250, 84, 8, 0,
+      4, 9, 10, 11, 12, 27, 27, 27, 27, 8, 40, 1]);
+  });
+
+  test('snapshot', (){
+    var flx = Builder();
+    flx.startVector();
+    flx.addInt(12);
+    expect(flx.snapshot().asUint8List(), [1, 12, 1, 44, 1]);
+    flx.addInt(24);
+    expect(flx.snapshot().asUint8List(), [12, 24, 2, 64, 1]);
+    flx.addInt(45);
+    expect(flx.snapshot().asUint8List(), [12, 24, 45, 3, 76, 1]);
+  });
+}
+

dart/test/flex_reader_test.dart

@@ -0,0 +1,316 @@
+import 'dart:typed_data';
+
+import 'package:flat_buffers/flex_buffers.dart' show Reference;
+import 'package:test/test.dart';
+
+void main() {
+  test('is null', () {
+    expect(Reference.fromBuffer(b([0, 0, 1])).isNull, isTrue);
+  });
+
+  test('bool value', () {
+    expect(Reference.fromBuffer(b([1, 104, 1])).boolValue, isTrue);
+    expect(Reference.fromBuffer(b([0, 104, 1])).boolValue, isFalse);
+  });
+  test('int value', () {
+    expect(Reference.fromBuffer(b([25, 4, 1])).intValue, 25);
+    expect(Reference.fromBuffer(b([231, 4, 1])).intValue, -25);
+    expect(Reference.fromBuffer(b([230, 8, 1])).intValue, 230);
+    expect(Reference.fromBuffer(b([230, 0, 5, 2])).intValue, 230);
+    expect(Reference.fromBuffer(b([1, 4, 5, 2])).intValue, 1025);
+    expect(Reference.fromBuffer(b([255, 251, 5, 2])).intValue, -1025);
+    expect(Reference.fromBuffer(b([1, 4, 9, 2])).intValue, 1025);
+    expect(Reference.fromBuffer(b([255, 255, 255, 127, 6, 4])).intValue,
+      2147483647);
+    expect(
+      Reference.fromBuffer(b([0, 0, 0, 128, 6, 4])).intValue, -2147483648);
+    expect(
+      Reference.fromBuffer(b([255, 255, 255, 255, 0, 0, 0, 0, 7, 8]))
+        .intValue,
+      4294967295);
+    expect(
+      Reference.fromBuffer(b([255, 255, 255, 255, 255, 255, 255, 127, 7, 8]))
+        .intValue,
+      9223372036854775807);
+    expect(Reference.fromBuffer(b([0, 0, 0, 0, 0, 0, 0, 128, 7, 8])).intValue,
+      -9223372036854775808);
+    // Dart does not really support UInt64
+//      expect(FlxValue.fromBuffer(b([255, 255, 255, 255, 255, 255, 255, 255, 11, 8])).intValue, 18446744073709551615);
+  });
+  test('double value', () {
+    expect(Reference.fromBuffer(b([0, 0, 144, 64, 14, 4])).doubleValue, 4.5);
+    expect(Reference.fromBuffer(b([205, 204, 204, 61, 14, 4])).doubleValue,
+      closeTo(.1, .001));
+    expect(
+      Reference.fromBuffer(b([154, 153, 153, 153, 153, 153, 185, 63, 15, 8]))
+        .doubleValue,
+      .1);
+  });
+  test('num value', () {
+    expect(Reference.fromBuffer(b([0, 0, 144, 64, 14, 4])).numValue, 4.5);
+    expect(Reference.fromBuffer(b([205, 204, 204, 61, 14, 4])).numValue,
+      closeTo(.1, .001));
+    expect(
+      Reference.fromBuffer(b([154, 153, 153, 153, 153, 153, 185, 63, 15, 8]))
+        .numValue,
+      .1);
+    expect(Reference.fromBuffer(b([255, 251, 5, 2])).numValue, -1025);
+  });
+  test('string value', () {
+    expect(
+      Reference.fromBuffer(b([5, 77, 97, 120, 105, 109, 0, 6, 20, 1]))
+        .stringValue,
+      'Maxim');
+    expect(
+      Reference.fromBuffer(b([
+        10, 104, 101, 108, 108, 111, 32, 240, 159, 152, 177, 0, 11, 20, 1
+      ])).stringValue,
+      'hello 😱');
+  });
+  test('blob value', () {
+    expect(
+      Reference.fromBuffer(b([3, 1, 2, 3, 3, 100, 1])).blobValue, [1, 2, 3]);
+  });
+  test('bool vector', () {
+    var flx = Reference.fromBuffer(b([3, 1, 0, 1, 3, 144, 1]));
+    expect(flx[0].boolValue, true);
+    expect(flx[1].boolValue, false);
+    expect(flx[2].boolValue, true);
+  });
+  test('number vector', () {
+    testNumbers([3, 1, 2, 3, 3, 44, 1], [1, 2, 3]);
+    testNumbers([3, 255, 2, 3, 3, 44, 1], [-1, 2, 3]);
+    testNumbers([3, 0, 1, 0, 43, 2, 3, 0, 6, 45, 1], [1, 555, 3]);
+    testNumbers(
+      [3, 0, 0, 0, 1, 0, 0, 0, 204, 216, 0, 0, 3, 0, 0, 0, 12, 46, 1],
+      [1, 55500, 3]);
+    testNumbers([
+      3, 0, 0, 0, 0, 0, 0, 0,
+      1, 0, 0, 0, 0, 0, 0, 0,
+      172, 128, 94, 239, 12, 0, 0, 0,
+      3, 0, 0, 0, 0, 0, 0, 0,
+      24, 47, 1
+    ], [1, 55555555500, 3
+    ]);
+    testNumbers(
+      [3, 0, 0, 0, 0, 0, 192, 63, 0, 0, 32, 64, 0, 0, 96, 64, 12, 54, 1],
+      [1.5, 2.5, 3.5]);
+    testNumbers([
+      3, 0, 0, 0, 0, 0, 0, 0,
+      154, 153, 153, 153, 153, 153, 241, 63,
+      154, 153, 153, 153, 153, 153, 1, 64,
+      102, 102, 102, 102, 102, 102, 10, 64,
+      24, 55, 1
+    ], [1.1, 2.2, 3.3
+    ]);
+  });
+  test('number vector, fixed type', () {
+    testNumbers([1, 2, 2, 64, 1], [1, 2]);
+    testNumbers([255, 255, 0, 1, 4, 65, 1], [-1, 256]);
+    testNumbers([211, 255, 255, 255, 0, 232, 3, 0, 8, 66, 1], [-45, 256000]);
+    testNumbers([
+      211, 255, 255, 255, 255, 255, 255, 255,
+      255, 255, 255, 255, 255, 255, 255, 127,
+      16, 67, 1
+    ], [
+      -45, 9223372036854775807
+    ]);
+
+    testNumbers([1, 2, 2, 68, 1], [1, 2]);
+    testNumbers([1, 0, 0, 1, 4, 69, 1], [1, 256]);
+    testNumbers([45, 0, 0, 0, 0, 232, 3, 0, 8, 70, 1], [45, 256000]);
+
+    testNumbers([205, 204, 140, 63, 0, 0, 0, 192, 8, 74, 1], [1.1, -2]);
+    testNumbers([
+      154, 153, 153, 153, 153, 153, 241, 63,
+      0, 0, 0, 0, 0, 0, 112, 192,
+      16, 75, 1
+    ], [
+      1.1, -256
+    ]);
+
+    testNumbers([211, 255, 255, 255, 0, 232, 3, 0, 4, 0, 0, 0, 12, 78, 1],
+      [-45, 256000, 4]);
+
+    testNumbers([
+      211, 255, 255, 255, 255, 255, 255, 255,
+      255, 255, 255, 255, 255, 255, 255, 127,
+      4, 0, 0, 0, 0, 0, 0, 0,
+      9, 0, 0, 0, 0, 0, 0, 0,
+      32, 91, 1
+    ], [
+      -45, 9223372036854775807, 4, 9
+    ]);
+
+    testNumbers([
+      45, 0, 0, 0, 0, 0, 0, 0,
+      255, 255, 255, 255, 255, 255, 255, 127,
+      4, 0, 0, 0, 0, 0, 0, 0,
+      9, 0, 0, 0, 0, 0, 0, 0,
+      32, 95, 1
+    ], [
+      45, 9223372036854775807, 4, 9
+    ]);
+
+    testNumbers([
+      154, 153, 153, 153, 153, 153, 241, 63,
+      0, 0, 0, 0, 0, 0, 112, 64,
+      0, 0, 0, 0, 0, 0, 16, 64,
+      24, 87, 1
+    ], [
+      1.1, 256, 4
+    ]);
+
+    testNumbers([
+      154, 153, 153, 153, 153, 153, 241, 63,
+      0, 0, 0, 0, 0, 0, 112, 64,
+      0, 0, 0, 0, 0, 0, 16, 64,
+      0, 0, 0, 0, 0, 0, 34, 64,
+      32, 99, 1
+    ], [
+      1.1, 256, 4, 9
+    ]);
+  });
+  test('string vector', () {
+    testStrings([
+      3, 102, 111, 111, 0,
+      3, 98, 97, 114, 0,
+      3, 98, 97, 122, 0,
+      3, 15, 11, 7,
+      3, 60, 1
+    ], [
+      'foo', 'bar', 'baz'
+    ]);
+    testStrings([
+      3, 102, 111, 111, 0,
+      3, 98, 97, 114, 0,
+      3, 98, 97, 122, 0,
+      6, 15, 11, 7, 18, 14, 10,
+      6, 60, 1
+    ], [
+      'foo', 'bar', 'baz', 'foo', 'bar', 'baz'
+    ]);
+  });
+  test('mixed vector', () {
+    var flx = Reference.fromBuffer(b([
+      3, 102, 111, 111, 0, 0, 0, 0,
+      5, 0, 0, 0, 0, 0, 0, 0,
+      15, 0, 0, 0, 0, 0, 0, 0,
+      1, 0, 0, 0, 0, 0, 0, 0,
+      251, 255, 255, 255, 255, 255, 255, 255,
+      205, 204, 204, 204, 204, 204, 244, 63,
+      1, 0, 0, 0, 0, 0, 0, 0,
+      20, 4, 4, 15, 104, 45, 43, 1
+    ]));
+    expect(flx.length, 5);
+    expect(flx[0].stringValue, 'foo');
+    expect(flx[1].numValue, 1);
+    expect(flx[2].numValue, -5);
+    expect(flx[3].numValue, 1.3);
+    expect(flx[4].boolValue, true);
+  });
+
+  test('single value map', () {
+    var flx = Reference.fromBuffer(b([97, 0, 1, 3, 1, 1, 1, 12, 4, 2, 36, 1]));
+    expect(flx.length, 1);
+    expect(flx['a'].numValue, 12);
+  });
+  test('two value map', () {
+    var flx = Reference.fromBuffer(b([0, 97, 0, 2, 4, 4, 2, 1, 2, 45, 12, 4, 4, 4, 36, 1]));
+    expect(flx.length, 2);
+    expect(flx['a'].numValue, 12);
+    expect(flx[''].numValue, 45);
+  });
+  test('complex map', () {
+    var flx = complexMap();
+    expect(flx.length, 5);
+    expect(flx['age'].numValue, 35);
+    expect(flx['weight'].numValue, 72.5);
+    expect(flx['name'].stringValue, 'Maxim');
+
+    expect(flx['flags'].length, 4);
+    expect(flx['flags'][0].boolValue, true);
+    expect(flx['flags'][1].boolValue, false);
+    expect(flx['flags'][2].boolValue, true);
+    expect(flx['flags'][3].boolValue, true);
+
+    expect(flx['address'].length, 3);
+    expect(flx['address']['city'].stringValue, 'Bla');
+    expect(flx['address']['zip'].stringValue, '12345');
+    expect(flx['address']['countryCode'].stringValue, 'XX');
+
+    expect(() => flx['address']['country'].stringValue,
+      throwsA(predicate((e) => e is ArgumentError && e.message == 'Key: [country] is not applicable on: //address of: ValueType.Map')));
+    expect(() => flx['address']['countryCode'][0],
+      throwsA(predicate((e) => e is ArgumentError && e.message == 'Key: [0] is not applicable on: //address/countryCode of: ValueType.String')));
+    expect(() => flx[1],
+      throwsA(predicate((e) => e is ArgumentError && e.message == 'Key: [1] is not applicable on: / of: ValueType.Map')));
+    expect(() => flx['flags'][4],
+      throwsA(predicate((e) => e is ArgumentError && e.message == 'Key: [4] is not applicable on: //flags of: ValueType.VectorBool length: 4')));
+    expect(() => flx['flags'][-1],
+      throwsA(predicate((e) => e is ArgumentError && e.message == 'Key: [-1] is not applicable on: //flags of: ValueType.VectorBool length: 4')));
+  });
+  test('complex map to json', () {
+    var flx = complexMap();
+    expect(flx.json, '{"address":{"city":"Bla","countryCode":"XX","zip":"12345"},"age":35,"flags":[true,false,true,true],"name":"Maxim","weight":72.5}');
+  });
+
+  test('complex map iterators', () {
+    var flx = complexMap();
+    expect(flx.mapKeyIterable.map((e) => e).toList(), ['address', 'age', 'flags', 'name', 'weight']);
+    expect(flx.mapValueIterable.map((e) => e.json).toList(), [flx['address'].json, flx['age'].json, flx['flags'].json, flx['name'].json, flx['weight'].json]);
+    expect(flx['flags'].vectorIterable.map((e) => e.boolValue).toList(), [true, false, true, true]);
+  });
+}
+
+ByteBuffer b(List<int> values) {
+  var data = Uint8List.fromList(values);
+  return data.buffer;
+}
+
+void testNumbers(List<int> buffer, List<num> numbers) {
+  var flx = Reference.fromBuffer(b(buffer));
+  expect(flx.length, numbers.length);
+  for (var i = 0; i < flx.length; i++) {
+    expect(flx[i].numValue, closeTo(numbers[i], 0.001));
+  }
+}
+
+void testStrings(List<int> buffer, List<String> numbers) {
+  var flx = Reference.fromBuffer(b(buffer));
+  expect(flx.length, numbers.length);
+  for (var i = 0; i < flx.length; i++) {
+    expect(flx[i].stringValue, numbers[i]);
+  }
+}
+
+Reference complexMap(){
+//  {
+//    "age": 35,
+//    "flags": [True, False, True, True],
+//    "weight": 72.5,
+//    "name": "Maxim",
+//    "address": {
+//      "city": "Bla",
+//      "zip": "12345",
+//      "countryCode": "XX",
+//    }
+//  }
+  return Reference.fromBuffer(b([
+  97, 100, 100, 114, 101, 115, 115, 0,
+      99, 105, 116, 121, 0, 3, 66, 108, 97, 0,
+      99, 111, 117, 110, 116, 114, 121, 67, 111, 100, 101, 0,
+      2, 88, 88, 0,
+      122, 105, 112, 0,
+      5, 49, 50, 51, 52, 53, 0,
+      3, 38, 29, 14, 3, 1, 3, 38, 22, 15, 20, 20, 20,
+      97, 103, 101, 0,
+      102, 108, 97, 103, 115, 0,
+      4, 1, 0, 1, 1,
+      110, 97, 109, 101, 0,
+      5, 77, 97, 120, 105, 109, 0,
+      119, 101, 105, 103, 104, 116, 0,
+      5, 93, 36, 33, 23, 12, 0, 0, 7, 0, 0, 0, 1, 0, 0, 0, 5, 0, 0, 0, 60, 0, 0, 0, 35, 0, 0, 0, 51, 0, 0, 0, 45,
+      0, 0, 0, 0, 0, 145, 66, 36, 4, 144, 20, 14, 25, 38, 1
+  ]));
+}

dart/test/flex_types_test.dart

@@ -0,0 +1,137 @@
+import 'package:flat_buffers/src/types.dart';
+import 'package:test/test.dart';
+
+void main() {
+  test('is inline', () {
+    expect(ValueTypeUtils.isInline(ValueType.Bool), isTrue);
+    expect(ValueTypeUtils.isInline(ValueType.Int), isTrue);
+    expect(ValueTypeUtils.isInline(ValueType.UInt), isTrue);
+    expect(ValueTypeUtils.isInline(ValueType.Float), isTrue);
+    expect(ValueTypeUtils.isInline(ValueType.Null), isTrue);
+    expect(ValueTypeUtils.isInline(ValueType.String), isFalse);
+  });
+  test('is type vector element', () {
+    expect(ValueTypeUtils.isTypedVectorElement(ValueType.Bool), isTrue);
+    expect(ValueTypeUtils.isTypedVectorElement(ValueType.Int), isTrue);
+    expect(ValueTypeUtils.isTypedVectorElement(ValueType.UInt), isTrue);
+    expect(ValueTypeUtils.isTypedVectorElement(ValueType.Float), isTrue);
+    expect(ValueTypeUtils.isTypedVectorElement(ValueType.Key), isTrue);
+    expect(ValueTypeUtils.isTypedVectorElement(ValueType.String), isTrue);
+
+    expect(ValueTypeUtils.isTypedVectorElement(ValueType.Null), isFalse);
+    expect(ValueTypeUtils.isTypedVectorElement(ValueType.Blob), isFalse);
+  });
+  test('is typed vector', () {
+    expect(ValueTypeUtils.isTypedVector(ValueType.VectorInt), isTrue);
+    expect(ValueTypeUtils.isTypedVector(ValueType.VectorUInt), isTrue);
+    expect(ValueTypeUtils.isTypedVector(ValueType.VectorFloat), isTrue);
+    expect(ValueTypeUtils.isTypedVector(ValueType.VectorBool), isTrue);
+    expect(ValueTypeUtils.isTypedVector(ValueType.VectorKey), isTrue);
+    expect(ValueTypeUtils.isTypedVector(ValueType.VectorString), isTrue);
+
+    expect(ValueTypeUtils.isTypedVector(ValueType.Vector), isFalse);
+    expect(ValueTypeUtils.isTypedVector(ValueType.Map), isFalse);
+    expect(ValueTypeUtils.isTypedVector(ValueType.Bool), isFalse);
+    expect(ValueTypeUtils.isTypedVector(ValueType.VectorInt2), isFalse);
+  });
+  test('is fixed typed vector', () {
+    expect(ValueTypeUtils.isFixedTypedVector(ValueType.VectorInt2), isTrue);
+    expect(ValueTypeUtils.isFixedTypedVector(ValueType.VectorInt3), isTrue);
+    expect(ValueTypeUtils.isFixedTypedVector(ValueType.VectorInt4), isTrue);
+    expect(ValueTypeUtils.isFixedTypedVector(ValueType.VectorUInt2), isTrue);
+    expect(ValueTypeUtils.isFixedTypedVector(ValueType.VectorUInt3), isTrue);
+    expect(ValueTypeUtils.isFixedTypedVector(ValueType.VectorUInt4), isTrue);
+    expect(ValueTypeUtils.isFixedTypedVector(ValueType.VectorFloat2), isTrue);
+    expect(ValueTypeUtils.isFixedTypedVector(ValueType.VectorFloat3), isTrue);
+    expect(ValueTypeUtils.isFixedTypedVector(ValueType.VectorFloat4), isTrue);
+
+    expect(ValueTypeUtils.isFixedTypedVector(ValueType.VectorInt), isFalse);
+  });
+  test('to typed vector', () {
+    expect(ValueTypeUtils.toTypedVector(ValueType.Int,0), equals(ValueType.VectorInt));
+    expect(ValueTypeUtils.toTypedVector(ValueType.UInt,0), equals(ValueType.VectorUInt));
+    expect(ValueTypeUtils.toTypedVector(ValueType.Bool,0), equals(ValueType.VectorBool));
+    expect(ValueTypeUtils.toTypedVector(ValueType.Float,0), equals(ValueType.VectorFloat));
+    expect(ValueTypeUtils.toTypedVector(ValueType.Key,0), equals(ValueType.VectorKey));
+    expect(ValueTypeUtils.toTypedVector(ValueType.String,0), equals(ValueType.VectorString));
+
+    expect(ValueTypeUtils.toTypedVector(ValueType.Int,2), equals(ValueType.VectorInt2));
+    expect(ValueTypeUtils.toTypedVector(ValueType.UInt,2), equals(ValueType.VectorUInt2));
+    expect(ValueTypeUtils.toTypedVector(ValueType.Float,2), equals(ValueType.VectorFloat2));
+
+    expect(ValueTypeUtils.toTypedVector(ValueType.Int,3), equals(ValueType.VectorInt3));
+    expect(ValueTypeUtils.toTypedVector(ValueType.UInt,3), equals(ValueType.VectorUInt3));
+    expect(ValueTypeUtils.toTypedVector(ValueType.Float,3), equals(ValueType.VectorFloat3));
+
+    expect(ValueTypeUtils.toTypedVector(ValueType.Int,4), equals(ValueType.VectorInt4));
+    expect(ValueTypeUtils.toTypedVector(ValueType.UInt,4), equals(ValueType.VectorUInt4));
+    expect(ValueTypeUtils.toTypedVector(ValueType.Float,4), equals(ValueType.VectorFloat4));
+  });
+  test('typed vector element type', () {
+    expect(ValueTypeUtils.typedVectorElementType(ValueType.VectorInt), equals(ValueType.Int));
+    expect(ValueTypeUtils.typedVectorElementType(ValueType.VectorUInt), equals(ValueType.UInt));
+    expect(ValueTypeUtils.typedVectorElementType(ValueType.VectorFloat), equals(ValueType.Float));
+    expect(ValueTypeUtils.typedVectorElementType(ValueType.VectorString), equals(ValueType.String));
+    expect(ValueTypeUtils.typedVectorElementType(ValueType.VectorKey), equals(ValueType.Key));
+    expect(ValueTypeUtils.typedVectorElementType(ValueType.VectorBool), equals(ValueType.Bool));
+  });
+  test('fixed typed vector element type', () {
+    expect(ValueTypeUtils.fixedTypedVectorElementType(ValueType.VectorInt2), equals(ValueType.Int));
+    expect(ValueTypeUtils.fixedTypedVectorElementType(ValueType.VectorInt3), equals(ValueType.Int));
+    expect(ValueTypeUtils.fixedTypedVectorElementType(ValueType.VectorInt4), equals(ValueType.Int));
+
+    expect(ValueTypeUtils.fixedTypedVectorElementType(ValueType.VectorUInt2), equals(ValueType.UInt));
+    expect(ValueTypeUtils.fixedTypedVectorElementType(ValueType.VectorUInt3), equals(ValueType.UInt));
+    expect(ValueTypeUtils.fixedTypedVectorElementType(ValueType.VectorUInt4), equals(ValueType.UInt));
+
+    expect(ValueTypeUtils.fixedTypedVectorElementType(ValueType.VectorFloat2), equals(ValueType.Float));
+    expect(ValueTypeUtils.fixedTypedVectorElementType(ValueType.VectorFloat3), equals(ValueType.Float));
+    expect(ValueTypeUtils.fixedTypedVectorElementType(ValueType.VectorFloat4), equals(ValueType.Float));
+  });
+  test('fixed typed vector element size', () {
+    expect(ValueTypeUtils.fixedTypedVectorElementSize(ValueType.VectorInt2), equals(2));
+    expect(ValueTypeUtils.fixedTypedVectorElementSize(ValueType.VectorInt3), equals(3));
+    expect(ValueTypeUtils.fixedTypedVectorElementSize(ValueType.VectorInt4), equals(4));
+
+    expect(ValueTypeUtils.fixedTypedVectorElementSize(ValueType.VectorUInt2), equals(2));
+    expect(ValueTypeUtils.fixedTypedVectorElementSize(ValueType.VectorUInt3), equals(3));
+    expect(ValueTypeUtils.fixedTypedVectorElementSize(ValueType.VectorUInt4), equals(4));
+
+    expect(ValueTypeUtils.fixedTypedVectorElementSize(ValueType.VectorFloat2), equals(2));
+    expect(ValueTypeUtils.fixedTypedVectorElementSize(ValueType.VectorFloat3), equals(3));
+    expect(ValueTypeUtils.fixedTypedVectorElementSize(ValueType.VectorFloat4), equals(4));
+  });
+  test('packed type', () {
+    expect(ValueTypeUtils.packedType(ValueType.Null, BitWidth.width8), equals(0));
+    expect(ValueTypeUtils.packedType(ValueType.Null, BitWidth.width16), equals(1));
+    expect(ValueTypeUtils.packedType(ValueType.Null, BitWidth.width32), equals(2));
+    expect(ValueTypeUtils.packedType(ValueType.Null, BitWidth.width64), equals(3));
+
+    expect(ValueTypeUtils.packedType(ValueType.Int, BitWidth.width8), equals(4));
+    expect(ValueTypeUtils.packedType(ValueType.Int, BitWidth.width16), equals(5));
+    expect(ValueTypeUtils.packedType(ValueType.Int, BitWidth.width32), equals(6));
+    expect(ValueTypeUtils.packedType(ValueType.Int, BitWidth.width64), equals(7));
+  });
+  test('bit width', () {
+    expect(BitWidthUtil.width(0), BitWidth.width8);
+    expect(BitWidthUtil.width(-20), BitWidth.width8);
+    expect(BitWidthUtil.width(127), BitWidth.width8);
+    expect(BitWidthUtil.width(128), BitWidth.width16);
+    expect(BitWidthUtil.width(128123), BitWidth.width32);
+    expect(BitWidthUtil.width(12812324534), BitWidth.width64);
+    expect(BitWidthUtil.width(-127), BitWidth.width8);
+    expect(BitWidthUtil.width(-128), BitWidth.width16);
+    expect(BitWidthUtil.width(-12812324534), BitWidth.width64);
+    expect(BitWidthUtil.width(-0.1), BitWidth.width64);
+    expect(BitWidthUtil.width(0.25), BitWidth.width32);
+  });
+  test('padding size', () {
+    expect(BitWidthUtil.paddingSize(10, 8), 6);
+    expect(BitWidthUtil.paddingSize(10, 4), 2);
+    expect(BitWidthUtil.paddingSize(15, 4), 1);
+    expect(BitWidthUtil.paddingSize(15, 2), 1);
+    expect(BitWidthUtil.paddingSize(15, 1), 0);
+    expect(BitWidthUtil.paddingSize(16, 8), 0);
+    expect(BitWidthUtil.paddingSize(17, 8), 7);
+  });
+}