about_arrays.rb

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

class AboutArrays < Neo::Koan
  def test_creating_arrays
    empty_array = Array.new
    assert_equal Array, empty_array.class
    assert_equal 0, empty_array.size
  end

  def test_array_literals
    array = Array.new
    assert_equal [], array

    array[0] = 1
    assert_equal [1], array

    array[1] = 2
    assert_equal [1, 2], array

    array << 333
    assert_equal [1, 2, 333], array

    # puts array << 444 << 555
    # output is
    # 1
    # 2
    # 333
    # 444
    # 555
  end

  def test_accessing_array_elements
    array = [:peanut, :butter, :and, :jelly]

    assert_equal :peanut, array[0]
    assert_equal :peanut, array.first
    assert_equal :jelly, array[3]
    assert_equal :jelly, array.last
    assert_equal :jelly, array[-1]
    assert_equal :butter, array[-3]

    # from Ruby doc...
    # "A negative index is assumed to be relative to the end of the array—that is, 
    # an index of -1 indicates the last element of the array, -2 is the next to
    # last element in the array, and so on."
  end

  def test_slicing_arrays
    array = [:peanut, :butter, :and, :jelly]

    # [start, length]
    assert_equal [:peanut], array[0,1]
    assert_equal [:peanut, :butter], array[0,2]
    assert_equal [:and, :jelly], array[2,2]
    assert_equal [:and, :jelly], array[2,20]
    assert_equal [], array[4,0]
    assert_equal [], array[4,100]
    assert_equal nil, array[5,0]
  end

  def test_arrays_and_ranges
    assert_equal Range, (1..5).class
    assert_not_equal [1,2,3,4,5], (1..5)
    assert_equal [1,2,3,4,5], (1..5).to_a
    assert_equal [1,2,3,4], (1...5).to_a # will exclude the end value
  end

  def test_slicing_with_ranges
    array = [:peanut, :butter, :and, :jelly]

    assert_equal [:peanut, :butter, :and], array[0..2]
    assert_equal [:peanut, :butter], array[0...2]
    assert_equal [:and, :jelly], array[2..-1]
  end

  def test_pushing_and_popping_arrays
    array = [1,2]
    array.push(:last)

    assert_equal [1, 2, :last], array

    popped_value = array.pop
    assert_equal :last, popped_value
    assert_equal [1, 2], array
  end

  def test_shifting_arrays
    array = [1, 2]
    array.unshift(:first)

    # from Ruby doc...
    # "Prepends objects to the front of self, moving other elements 
    # upwards. See also #shift for the opposite effect."

    assert_equal [:first, 1, 2], array

    shifted_value = array.shift
    assert_equal :first, shifted_value
    assert_equal [1, 2], array
  end

end