Assorted code writen during a Ruby lecture

collection.rb

class Song
  attr_reader :name, :artist, :genre, :subgenre, :tags

  def initialize(name, artist, genre, subgenre, tags)
    @name     = name
    @artist   = artist
    @genre    = genre
    @subgenre = subgenre
    @tags     = tags
  end
end

class Collection
  def initialize(songs)
    @songs = songs
  end

  def first
    @songs.first
  end

  def self.parse(input)
    songs = input.lines.map do |line|
      name, artist, genre_and_subgenre, tags_as_string = line.split('.').map(&:strip)
      genre, subgenre = genre_and_subgenre.split(',').map(&:strip)
      tags = if tags_as_string.nil?
        []
      else
        tags_as_string.split(',').map(&:strip)
      end

      Song.new name, artist, genre, subgenre, tags
    end

    new songs
  end
end

collection_test.rb

require 'minitest/unit'
require './collection'

INPUT = <<END
My Favourite Things.          John Coltrane.      Jazz, Bebop.        popular, cover
Greensleves.                  John Coltrane.      Jazz, Bebop.        popular, cover
Alabama.                      John Coltrane.      Jazz, Avantgarde.   melancholic
Acknowledgement.              John Coltrane.      Jazz, Avantgarde
Afro Blue.                    John Coltrane.      Jazz.               melancholic
'Round Midnight.              John Coltrane.      Jazz
My Funny Valentine.           Miles Davis.        Jazz.               popular
Tutu.                         Miles Davis.        Jazz, Fusion.       weird, cool
Miles Runs the Voodoo Down.   Miles Davis.        Jazz, Fusion.       weird
Boplicity.                    Miles Davis.        Jazz, Bebop
Autumn Leaves.                Bill Evans.         Jazz.               popular
Waltz for Debbie.             Bill Evans.         Jazz
'Round Midnight.              Thelonious Monk.    Jazz, Bebop
Ruby, My Dear.                Thelonious Monk.    Jazz.               saxophone
Fur Elise.                    Beethoven.          Classical.          popular
Moonlight Sonata.             Beethoven.          Classical.          popular
Pathetique.                   Beethoven.          Classical
Toccata e Fuga.               Bach.               Classical, Baroque. popular
Goldberg Variations.          Bach.               Classical, Baroque
Eine Kleine Nachtmusik.       Mozart.             Classical.          popular, violin
END

class CollectionTest < MiniTest::Unit::TestCase
# My Favourite Things.          John Coltrane.      Jazz, Bebop.        popular, cover
  def test_parsing_a_collection_file
    collection = Collection.parse(INPUT)
    song = collection.first

    assert_equal 'My Favourite Things', song.name
    assert_equal 'John Coltrane', song.artist
    assert_equal 'Jazz', song.genre
    assert_equal 'Bebop', song.subgenre
    assert_equal %w[popular cover], song.tags
  end

  def test_tags_is_an_empty_array_if_not_specified
    input = 'Acknowledgement. John Coltrane. Jazz, Avantgarde'
    collection = Collection.parse(input)

    song = collection.first

    assert_equal song.tags, []
  end
end

rat.rb

require './tests'

class Rat
  attr_reader :num, :den

  def initialize(num, den)
    gcd = num.gcd den
    @num = num / gcd
    @den = den / gcd
  end

  def ==(other)
    num == other.num and den == other.den 
  end

  def +(other)
    Rat.new num * other.den + other.num * den, den * other.den
  end

  def -(other)
    self + -other
  end

  def -@
    Rat.new(-num, den)
  end
end

ok Rat.new(1, 2).num == 1
ok Rat.new(1, 2).den == 2

ok Rat.new(1, 2) == Rat.new(1, 2)
ok Rat.new(3, 2) != Rat.new(1, 2)
ok Rat.new(1, 3) != Rat.new(1, 2)

ok Rat.new(1, 2) == Rat.new(2, 4)
ok Rat.new(15, 20) == Rat.new(9, 12)

ok Rat.new(1, 2) + Rat.new(3, 4) == Rat.new(5, 4)
ok Rat.new(1, 2) + Rat.new(1, 2) == Rat.new(1, 1)

ok Rat.new(3, 4) - Rat.new(1, 2) == Rat.new(1, 4)

ok(-Rat.new(3, 4) == Rat.new(-3, 4))