def path_to_url
      prefix = Jammit.asset_roots.map{ |path| Regexp.escape(path) }.uniq.join("|")
      @path_to_url ||= /\A(#{prefix})(\/?#{Regexp.escape(Jammit.public_root.sub(/#{prefix}/, ''))})?/
    end
def path_to_url
      prefix = Jammit.asset_roots.map{ |path| Regexp.escape(path) }.uniq.join("|")
      @path_to_url ||= /\A(#{prefix})(\/?#{Regexp.escape(Jammit.public_root.sub(/#{prefix}/, ''))})?/
    end
In Rails, the difference between a path and an asset URL is "public".