I am little confused while writing a simple class as below:

class NewsSource {
  final String url;
  final String name;
  final String imageUrl;
  NewsSource({required this.url, required this.name, required this.imageUrl});
  factory NewsSource.fromFireStore(
      DocumentSnapshot<Map<String, dynamic>> snapshot,
      SnapshotOptions? options) {
    final data = snapshot.data();
    return NewsSource(
        url: data?['url'], name: data?['name'], imageUrl: data?['imageUrl']);
  }
  Map<String, dynamic> toFireStore() {
    return {"url": url, "name": name, "imageUrl": imageUrl};
  }
}

fromFireStore function call NewsSource constructor where parameters can be null clearly but still dart is not complaining why?

PS: If I remove dynamic then it starts to complain, I guess any use of dynamic makes null check redundant.

CodePudding user response：

This: Map<String, dynamic> toFireStore() is mapping every type to a dynamic, which is not null-safe.

Dynamic allows non-nullable or nullable types assigned.

Unofficial Dart Documentation

CodePudding user response：

It's because of dynamic. Variables of type dynamic are basically not null-safe and still need to be handled accordingly.

My guess is that if we assume the map is not null then data?['url'] would return a variable of type dynamic for which null is also a valid value. And variables of type dynamic are never checked for null-safety. So it doesn't even bother to complain whether the map is null