懒洋洋地枚举,直到块为假

class Pager
  include Enumerable

  def initialize(&fetch_next_page)
    @fetch_next_page = fetch_next_page
    reset
  end

  def reset
    @page_number = 0
  end

  private def next_page
    @page_number += 1

    return @fetch_next_page.call(@page_number)
  end

  def each(&block)
    if block_given?
      while resp = next_page
        resp.each(&block)
      end
      reset
    else
      to_enum(:each)
    end
  end
end

下面是一个如何使用它的示例。

pager = Pager.new do |page_number|
  response = fetch_page( page: page_number, **some_options )

  response.page <= response.total_pages ? response.stuff : false
end

pager = Pager.new { |page_number|
  page_number <= 3 ? 1.upto(page_number) : false
}

# [1, 1, 2, 1, 2, 3]
puts pager.to_a.inspect

有没有更简单的方法?我已经接近了枚举器,但无法得到平坦的工作。

def paginate(&fetch_next)
  return Enumerator.new do |yielder|
    page_number = 1
    while ret = fetch_next.call(page_number)
      yielder.yield(*ret)
      page_number += 1
    end
  end
end

pager = paginate { |page_number|
  page_number <= 3 ? 1.upto(page_number) : false
}

# [1, [1, 2], [1, 2, 3]]
puts pager.to_a.inspect