Ruby idiom to shortcircuit使用each和map返回第一个非nil

Question

这是我想要做的事情的本质,但"休息"不能正确地进行:

needle = nil
haystacks.each do |haystack|
  needle = haystack.look_for_needle()
  break if needle
end

这个更短,但它会迭代每个干草堆(至少看不到),即使它不需要:

needle = nil
haystacks.each do |haystack|
  needle ||= haystack.look_for_needle()
end

这是一个单行,但(我相信)它不是懒惰,所以它做了不必要的工作:

needle = hackstacks.map{|h| h.look_for_needle()}.detect{|x| !x.nil?}

我觉得应该有一个班轮,但我不确定它会是:

needle = hackstacks.some_find_each_first_detect_lazy_map_thingee {|h| h.look_for_needle()}

Answer 1

使用Ruby 2.x 懒惰枚举器:

needle = haystacks.lazy.map(&:look_for_needle).reject(&:nil?).first

要么:

needle = haystacks.lazy.map(&:look_for_needle).detect { |needle| !needle.nil? }

要么:

needle = haystacks.lazy.map(&:look_for_needle).detect(&:itself)

Answer 2

haystack.find &:itself
haystack.index &:itself

你更倾向哪个？