Lunacy? Or OO?

gistfile1.rb

# Deciding how to handle a collection based on its size.
#
# Inspired by http://silkandspinach.net/2012/07/06/hexagonal-rails-hiding-the-finders/
#
# See below for usage

module Demux
  def demux(demux, outputs = nil, &block)
    if outputs && block_given?
      raise ArgumentError, "Pass either a block or an object, not both"
    elsif outputs
      demux.demux_outputs outputs
    elsif block_given?
      demux.demux_block &block
    else
      raise ArgumentError, "Pass either a block or an object"
    end

    demux
  end
end

module SizeDemux
  include Demux

  # Inspect collection size and pick the appropriate line.
  #
  # Available lines:
  #   * zero                 - if the collection is empty
  #   * non_zero(collection) - if the collection is not empty
  #   * one(element)         - if the collection has a single element
  #   * many(collection)     - if the collection has more than one element
  #
  # Usage:
  #   
  # collection.demux_size do |outputs|
  #   outputs.zero     { ... }
  #   outputs.non_zero { |collection| ... }
  #   ...
  # end
  #
  # # or
  #
  # class Demuxed
  #   def zero
  #     ...
  #   end
  #
  #   def non_zero(collection)
  #     ...
  #   end
  # end
  #
  # collection.demux_size(Demuxed.new)
  #
  def demux_size(outputs = nil, &block)
    demux(SizeDemux.new(self), outputs, &block)
  end

  class SizeDemux
    LINES = %w(zero non_zero one many)

    def initialize(collection)
      @collection = collection
    end

    def demux_block
      yield self
    end

    def demux_outputs(outputs)
      LINES.each do |line|
        send(line) { |*args| outputs.send(line, *args) }
      end
    end

    def zero
      yield if @collection.size == 0
    end

    def non_zero
      yield @collection if @collection.size > 0
    end

    def one
      yield @collection.first if @collection.size == 1
    end

    def many
      yield @collection if @collection.size > 1
    end
  end
end