Generics, Futures, Extensions in Dart

main.dart

void main() async {
  //Dynamic List
  var list = [];
  list.add(1);
  list.add('2');
  print(list);

  // Callbacks
  void downloadImage(Function(int) callback) {
    int progress = 0;

    while (progress < 100) {
      progress++;
      callback(progress);
    }
  }

  downloadImage((progress) => print(progress));
  downloadImage(print);
  downloadImage((progress) {
    final text = '$progress%';
    print(text);
  });

  // Generics
  ImageSize size = stringToEnum("medium", ImageSize.values);
  print(size.resolution);

  PostType post = stringToEnum("video", PostType.values);
  print(post);

  print(ImageSizeExtension.getMaxResolution());

  // Null Safety
  int a = 1;
  int b = null;
  print(a + (b ?? 0));

  print(b?.abs());

  b ??= 0;
  print(a + b);

  // Async Functions

  countSeconds(5);
  await printOrderMessage();
}

T stringToEnum<T>(String str, Iterable<T> values) {
  return values.firstWhere(
    (value) => value.toString().split('.')[1] == str,
    orElse: () => null,
  );
}

enum ImageSize { small, medium, large }

enum PostType { picture, video, reel }

// Extension

extension ImageSizeExtension on ImageSize {
  int get resolution {
    switch (this) {
      case ImageSize.small:
        return 300;
      case ImageSize.medium:
        return 700;
      case ImageSize.large:
        return 1024;
    }
  }

  static int getMaxResolution() => ImageSize.large.resolution;
}

void countSeconds(int s) {
  for (var i = 1; i <= s; i++) {
    Future.delayed(Duration(seconds: i), () => print(i));
  }
}

Future<void> printOrderMessage() async {
  print('Awaiting user order...');
  var order = await fetchUserOrder();
  print('Your order is: $order');
}

Future<String> fetchUserOrder() {
  return Future.delayed(Duration(seconds: 4), () => 'Large Latte');
}