foo_bar.cr

class FooBar
  def initialize(@value = 0)
  end
  
  def value
    @value
  end
  
  protected def value=(val)
    @value = val
  end
end

foo_bar_serializer.cr

abstract class Serializer(Type)
  def initialize(@output)
  end
  
  def write(obj : Type)
    # Add meta data here?
    write_data(obj)
  end
  
  abstract def write_data(obj : Type)
end


class FooBar
  class Serializer < Serializer(FooBar)
    def write_data(obj : FooBar)
      @output[:value] = obj.value
    end
  end
end