My (broken) solution for http://www.codewars.com/kata/520d623fdf58c68c6f00013e/

BatchItemProcessor.rb

class BatchItemProcessor
  attr_accessor :processed_items

  def initialize
    reset
  end

  def process_items items
    items.each do |item|
      identifier=@identifier.call(item)
      unless @processed_items.include? identifier
        @processed_items.push identifier
        yield item if @processor.call(item)
      end
    end
  end

  def reset
    @processed_items = []
    @identifier = proc{|x| x}
    @processor = proc{|x| true}
  end

  def identify identifier
    @identifier = proc{|x| x.is_a?(Hash) ? x[identifier] : x.send(identifier)}
  end

  def should_process &block
    @processor = block
  end
end