Dart Map::clone to make it mutable.

main.dart

void main() {
  const Map<String, dynamic> a = {
    'value': 1,
    'test': {
      'asd': 'asd',
    }
  };
  var b = a.clone(unmodifiable: false);
  var c = a.clone(unmodifiable: true);
  
  print(b);
  b['test']['asd'] = '123';
  b['test']['sdf'] = true;
  print(b);
  
  // error
//   c['test']['asd'] = '123';
}

extension MapExt<K, V> on Map {
  Map<K, V> clone({bool unmodifiable = false}) {
    dynamic iterate(node) =>
        node.map((k, v) => v is Map ? MapEntry(k, iterate(v)) : MapEntry(k, v));
    return unmodifiable ? Map.unmodifiable(this) : iterate(this);
  }
}