main.dart

enum Alignment { center }

// Domain model
class Image {
  final int width;
  final Alignment alignment;

  Image({required this.width, required this.alignment});
}

// JSON model
// 1. lazy deserialization
// 2. implements domain model, no need for converters
// 3. contains the JSON map, no need for serialization
//
// TODO memoisation to prevent double parsing
class ImageJsonView implements Image {
  final Map json;

  @override
  int get width => json['width'] ?? (throw 'parse error');

  @override
  Alignment get alignment =>
      json['align'] == 'center' ? Alignment.center : (throw 'parse error');

  ImageJsonView(this.json);
  
  @override
  String toString() => 'ImageJsonView$json';
}

void main() {
  final Image image = ImageJsonView({
    "width": 100,
    "align": "center",
  });
  
  print(image);
}