operator [] method

@override SunnyObservableMap<K, V>? operator [](Object? key)

The value for the given key, or null if key is not in the map.

Some maps allow null as a value. For those maps, a lookup using this operator cannot distinguish between a key not being in the map, and the key being there with a null value. Methods like containsKey or putIfAbsent can be used if the distinction is important.

Implementation

@override
SunnyObservableMap<K, V>? operator [](Object? key) {
  final k = key as K1?;
  return putIfAbsent(key, () {
    final map = SunnyObservableMap<K, V>(
      diffDelegator: listDiffDelegator,
      debugLabel: "$debugLabel[$key]",
    );
    addDisposer(map.changeStream.listen((changes) {
      changeController.add(newBuilder()..change(k, map));
    }).cancel);
    return map;
  });
}