Iterable<String> keys

The keys of this.

The returned iterable has efficient length and contains operations, based on length and containsKey of the map.

The order of iteration is defined by the individual Map implementation, but must be consistent between changes to the map.

Modifying the map while iterating the keys may break the iteration.

Source 

Iterable<String> get keys {
  final keys = <String>[];
  forEach((k, v) => keys.add(k));
  return keys;
}