Object from Mapping topic

The parser pushes a map's key and value at the same time after parsing them into a MappingToObject<K, V, T> delegate via its accept method.

YamlSet example

The example is meant to provide the gist on how to implement a MappingToObject. This code can be found in the example/yaml_set.dart file.

Most (if not all) programming languages use a hashtable under-the-hood to implement a set which YAML mentions but doesn't include as part of the official YAML 1.2 spec. Let's create a generic set that accepts elements.

• The delegate

final class YamlSet<T> extends MappingToObject<T, T?, Set<T>> {
  final _set = <T>{};

  @override
  bool accept(T key, T? value) {
    _set.add(key);
    return true;
  }

  @override
  Set<T> parsed() => _set;
}

• Binding it to the tag. The package exports the !!set tag which was supported in earlier YAML 1.1.* versions.

// {hello, world}
print(
  loadDartObject<Set<String>>(
    // flow map
    YamlSource.string('$setTag { hello, hello, world, world }'),
    triggers: CustomTriggers(
      advancedResolvers: {
        setTag: ObjectFromMap(
          onCustomMap: () => YamlSet<String>(),
        ),
      },
    ),
  ),
);

print(
  // {10, 20, 24}
  loadDartObject<Set<int>>(
    // block maps
    YamlSource.string('''
$setTag
? 10
? 10
? 20
? 24
'''),
    triggers: CustomTriggers(
      advancedResolvers: {
        setTag: ObjectFromMap(
          onCustomMap: () => YamlSet<int>(),
        ),
      },
    ),
  )
);

Classes

CustomTriggers

A class with callbacks to some of the inner workings of the parser.

MappingToObject<K, V, T>

A delegate that directly maps a YAML map to an object T and accepts an object key K and object value V. No intermediate Map is constructed. Both the key and value are presented at the same time after the complete entry has been parsed. You must override the parsed method.

ObjectFromMap<K, V, T>

A resolver that creates a delegate that accepts a key-value pair.