def srcset
      return '' unless sources_photos.kind_of? Array
      @srcset ||= source_photos.inject([]) do |res, photo| 
        res << [photo.id, photo.sizing].join(' ')
      end.join(',')
    end
def srcset
      return '' unless sources_photos.kind_of? Array
      @srcset ||= source_photos.inject([]) do |res, photo| 
        res << [photo.id, photo.sizing].join(' ')
      end.join(',')
    end
map [{src: 'banner-HD.jpeg', sizing: '2x'}, {src: 'banner-phone.jpeg', sizing: '100w'}]
 into -> "banner-HD.jpeg 2x, banner-phone.jpeg 100w