Ruby idiom to shortcircuit to return first non-nil using each and map

With Ruby 2.x lazy enumerators:

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

Or:

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

Or:

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

haystack.find &:itselfhaystack.index &:itself

Which one do you prefer?

I assume that both find_proverbial_needle_in_a_haystack and look_for_needle return the needle or nil, the latter if no haystack contains the needle.

class Haystack  def initialize(haystack)    @haystack = haystack  end  # Suppose look_for_needle is defined as follows  def look_for_needle    @haystack.include?(:straw) && :straw  end enddef find_proverbial_needle_in_a_haystack(haystacks)  needle = nil # can be anything  haystacks.find { |haystack| needle = haystack.look_for_needle } && needleend

find returns the first haystack for which the block evaluates true, or nil if no needle is found in any haystack.

haystacks = [Haystack.new([:ball, :top]),             Haystack.new([:fluff, :straw]),             Haystack.new([:dog, :cat])]  #=> [#<Haystack:0x007fdaaa0f6860 @haystack=[:ball, :top]>,  #    #<Haystack:0x007fdaaa0f67e8 @haystack=[:fluff, :straw]>,  #    #<Haystack:0x007fdaaa0f6590 @haystack=[:dog, :cat]>] find_proverbial_needle_in_a_haystack(haystacks)  #=> :straw haystacks = [Haystack.new([:ball, :top]),             Haystack.new([:fluff, :yellow_stuff]),             Haystack.new([:dog, :cat])]  #=> [#<Haystack:0x007fdaaa082f50 @haystack=[:ball, :top]>,  #    #<Haystack:0x007fdaaa082f00 @haystack=[:fluff, :yellow_stuff]>,  #    #<Haystack:0x007fdaaa082eb0 @haystack=[:dog, :cat]>]     find_proverbial_needle_in_a_haystack(haystacks)  #=> nil