Skip to content

Tree Converters

Tree converters are a special type of converter that can be used to convert a complex type tree structure. To register a tree converter, you must call the registerTreeBaseFactory method of the DogEngine. This method takes a Type and a TreeBaseConverterFactory instance as arguments. For more details on when tree converters are used, refer to the Field Serialization

List Converter using createIterableFactory

final listFactory = TreeBaseConverterFactory.createIterableFactory<List>(
  wrap: <T>(Iterable<T> entries) => entries.toList(),
  unwrap: <T>(List value) => value,
Iterable converters are the most basic and also the most common type of tree converters. They are easy to create and can be used to convert any type of iterable. The wrap and unwrap functions are used to convert the iterable to and from the tree's base type.

Map Converter using NTreeArgConverter

final mapFactory = TreeBaseConverterFactory.createNargsFactory<Map>(
  nargs: 2, consume: <K, V>() => MapNTreeArgConverter<K, V>()

class MapNTreeArgConverter<K,V> extends NTreeArgConverter<Map> {
  Map deserialize(value, DogEngine engine) {
    return (value as Map).map<K,V>((key, value) => MapEntry<K,V>(
      deserializeArg(key, 0, engine),
      deserializeArg(value, 1, engine),

  serialize(Map value, DogEngine engine) {
    return, value) => MapEntry(
      serializeArg(key, 0, engine),
      serializeArg(value, 1, engine),
NTreeArgConverters are used to convert complex types that have a fixed number of type arguments. The consume method is used to expand the stored type arguments to usable generic type arguments which then need to be used to create a NTreeArgConverter. The NTreeArgConverter class provides the deserializeArg and serializeArg methods to convert generic items using the converter associated with the type argument at the given index.

Complex Container using NTreeArgConverter

final containerFactory = TreeBaseConverterFactory.createNargsFactory<Container>(
  nargs: 3,
  consume: <A,B,C>() => ContainerConverter<A,B,C>(),

class Container<A,B,C> {
  final A a;
  final B b;
  final C c;

  Container(this.a, this.b, this.c);

  String toString() => "Container<$A, $B, $C>($a, $b, $c)";

class ContainerConverter<A,B,C> extends NTreeArgConverter<Container> {

  Container deserialize(value, DogEngine engine) {
    return Container<A,B,C>(
      deserializeArg(value["a"], 0, engine),
      deserializeArg(value["b"], 1, engine),
      deserializeArg(value["c"], 2, engine),

  serialize(Container value, DogEngine engine) {
    return {
      "a": serializeArg(value.a, 0, engine),
      "b": serializeArg(value.b, 1, engine),
      "c": serializeArg(value.c, 2, engine)