http://blog.jerodsanto.net/2012/05/enumerables-star-ect-methods-reimplemented-using-each_with_object/

star_ect_with_object.rb

require "minitest/autorun"

module Enumerable
  def collect(&block)
    each_with_object([]) { |i, obj| obj << block.call(i) }
  end

  def detect(&block)
    # each_with_object(nil) { |i, obj| obj ||= block.call(i) ? i : nil }
    inject(nil) { |obj, i| obj ||= block.call(i) ? i : nil; obj }
  end

  def select(&block)
    each_with_object([]) { |i, obj| obj << i if block.call(i) }
  end

  def reject(&block)
    each_with_object([]) { |i, obj| obj << i unless block.call(i) }
  end
end

class StarEctTest < MiniTest::Unit::TestCase
  def setup
    @array = [1, 2, 3, 4, 5]
  end

  def test_collect
    assert_equal [2, 4, 6, 8, 10], @array.collect { |i| i * 2 }
  end

  def test_detect
    assert_equal 3, @array.detect { |i| i > 2 }
    assert_nil @array.detect { |i| i < 0 }
  end

  def test_select
    assert_equal [1, 2], @array.select { |i| i < 3 }
    assert_equal [],  @array.select { |i| i < 0 }
  end

  def test_reject
    assert_equal [3, 4, 5], @array.reject { |i| i < 3 }
    assert_equal [], @array.reject { |i| i > 0 }
  end
end