about_iteration.rb

require File.expand_path(File.dirname(__FILE__) + '/neo')

class AboutIteration < Neo::Koan

  # -- An Aside ------------------------------------------------------
  # Ruby 1.8 stores names as strings. Ruby 1.9 stores names as
  # symbols. So we use a version dependent method "as_name" to convert
  # to the right format in the koans.  We will use "as_name" whenever
  # comparing to lists of methods.

  in_ruby_version("1.8") do
    def as_name(name)
      name.to_s
    end
  end

  in_ruby_version("1.9", "2.0", "2.1") do
    def as_name(name)
      name.to_sym
    end
  end

  # Ok, now back to the Koans.
  # -------------------------------------------------------------------

  def test_each_is_a_method_on_arrays
    assert_equal true, [].methods.include?(as_name(:each))
  end

  def test_iterating_with_each
    array = [1, 2, 3]
    sum = 0
    array.each do |item|
      sum += item
    end
    assert_equal 6, sum
  end

  def test_each_can_use_curly_brace_blocks_too
    array = [1, 2, 3]
    sum = 0
    array.each { |item| sum += item }
    assert_equal 6, sum
  end

  def test_break_works_with_each_style_iterations
    array = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
    sum = 0
    array.each do |item|
      break if item > 3
      sum += item
    end
    assert_equal 6, sum
  end

  def test_collect_transforms_elements_of_an_array
    array = [1, 2, 3]
    new_array = array.collect { |item| item + 10 }
    assert_equal [11,12,13], new_array

    # NOTE: 'map' is another name for the 'collect' operation
    another_array = array.map { |item| item + 10 }
    assert_equal new_array, another_array
  end

  def test_select_selects_certain_items_from_an_array
    array = [1, 2, 3, 4, 5, 6]

    even_numbers = array.select { |item| (item % 2) == 0 }
    assert_equal [2,4,6], even_numbers

    # NOTE: 'find_all' is another name for the 'select' operation
    more_even_numbers = array.find_all { |item| (item % 2) == 0 }
    assert_equal even_numbers, more_even_numbers
  end

  def test_find_locates_the_first_element_matching_a_criteria
    array = ["Jim", "Bill", "Clarence", "Doug", "Eli"]

    assert_equal "Clarence", array.find { |item| item.size > 4 }
  end

  def test_inject_will_blow_your_mind
    result = [2, 3, 4].inject(0) { |sum, item| sum + item }
    assert_equal 9, result

    result2 = [2, 3, 4].inject(1) { |product, item| product * item }
    assert_equal 24, result2

    # Extra Credit:
    # Describe in your own words what inject does.
    #
    # Blew. My. Mind.
    # But really it does a couple things depending on what it's passed.
    # If passed a method name as a symbol it will "inject" that method
    # between each element. Example: [1,2,3].inject(:+) will result in
    # 1.+(2).+(3) or better read as 1 + 2 + 3. If passed a block it
    # uses the 1st block value as an accumulator and the second to
    # represent the elements in the enumerable and the accumulator
    # value is assigned the result of whatever the operation in the
    # block returns. If no value is passed as an argument to inject,
    # the accumulator will represent the 1st value in the enum.
    # Example [1,2].inject { |acc,val| acc + val } will result in
    # acc = 1, val = 2 => acc = acc + val => 3
    # And [1,2].inject(3) { |acc,val| acc + val } will result in
    # acc=3, val=1 => acc += val => acc=4, val=2, => acc += val => 6
  end

  def test_all_iteration_methods_work_on_any_collection_not_just_arrays
    # Ranges act like a collection
    result = (1..3).map { |item| item + 10 }
    assert_equal [11,12,13], result

    # Files act like a collection of lines
    File.open("example_file.txt") do |file|
      upcase_lines = file.map { |line| line.strip.upcase }
      assert_equal %w[THIS IS A TEST], upcase_lines
    end

    # NOTE: You can create your own collections that work with each,
    # map, select, etc.
  end

  # Bonus Question:  In the previous koan, we saw the construct:
  #
  #   File.open(filename) do |file|
  #     # code to read 'file'
  #   end
  #
  # Why did we do it that way instead of the following?
  #
  #   file = File.open(filename)
  #   # code to read 'file'
  #
  # When you get to the "AboutSandwichCode" koan, recheck your answer.
  #
  # Because passing File.open a block causes the file to automatically
  # be closed when the block terminates and the value of the block is
  # returned by File.open.

end