operator [] method Null safety
- Object? key
Retrieves the zone-value associated with key.
If this zone does not contain the value looks up the same key in the
parent zone. If the key is not found returns null.
Any object can be used as key, as long as it has compatible operator ==
and hashCode implementations.
By controlling access to the key, a zone can grant or deny access to the
zone value.
Implementation
dynamic operator [](Object? key);