anchor.diff:        title.hashCode ^ artist.hashCode ^ album.hashCode ^ image.hashCode;
   
     Metas copyWith({
  +    String id,
       String title,
       String artist,
       String album,
  
positive.code:     MetasImage image,
    }) {
      return new Metas(
        title: title ?? this.title,
        artist: artist ?? this.artist,
        album: album ?? this.album,
  
negative.code: 
  @immutable
  class Metas {
    final String id;
    final String title;
    final String artist;
    final String album;
  