operator [] method Null safety

  1. @override
V? operator [](
  1. Object? key
)
override

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
V? operator [](Object? key) {
  for (var map in _maps) {
    // Avoid two hash lookups on a positive hit.
    var value = map[key];
    if (value != null || map.containsKey(value)) {
      return value;
    }
  }
  return null;
}