Question

i’ve been following the code examples in the pickaxe book but have been recently stumped by a bug in my code.

after adding this line of code (at ~line 60 in the full file, below) —

@index.add_to_index(song, song.name, song.artist)

i receive this error:

Loaded suite ruby_juke
Started
E
Finished in 0.000213 seconds.

  1) Error:
test_delete(TestSongList):
NoMethodError: undefined method `name' for #<Song:0x10cd95eb0>
    ruby_juke.rb:60:in `append'
    ruby_juke.rb:163:in `test_delete'

1 tests, 0 assertions, 0 failures, 1 errors

my question is, what is that one line of code doing to cause the error?

if you can help, feel free to send hints, links to hints, ask me questions, etc.

thanks!
-d

p.s. in case it helps, here are the contents of my ruby_juke.rb program:

#!/usr/local/bin/ruby -w

class Song

  attr_writer :duration

  @@plays = 0

  def initialize(name, artist, duration)
    @name     = name
    @artist   = artist
    @duration = duration
    @plays    = 0
  end

  def play
    @plays  += 1   # same as @plays = @plays + 1
    @@plays += 1
    "this song: #@plays plays. total #@@plays plays."
  end

  def duration_in_minutes
    @duration/60.0    # force floating point
  end

  def duration_in_minutes=(new_duration)
    @duration = (new_duration*60).to_i
  end

  def to_s
    "song: #@name--#@artist (#@duration)"
  end

end

class KaraokeSong < Song

  def initialize(name, artist, duration, lyrics)
    super(name, artist, duration)
    @lyrics = lyrics
  end

  # format ourselves as a string by appending
  # our lyrics to our parent's #to_s value.
  def to_s
    super + " [#@lyrics]"
  end

end

class SongList

  def initialize
    @songs = Array.new
    @index = WordIndex.new
  end

  def append(song)
    @songs.push(song)
    @index.add_to_index(song, song.name, song.artist)
    self
  end

  def lookup(word)
    @index.lookup(word)
  end

  def delete_first
    @songs.shift
  end

  def delete_last
    @songs.pop
  end

  def [](index)
    @songs[index]
  end

  def with_title(title)
    @songs.find {|song| title == song.name }
  end

  MAX_TIME = 5*60        # 5 minutes

  def SongList.is_too_long(song)
    return song.duration > MAX_TIME
  end

end

class WordIndex

  def initialize
    @index = {}
  end

  def add_to_index(obj, *phrases)
    phrases.each do |phrase|
      phrase.scan(/\w[-w']+/) do |word|      # extract each word
        word.downcase!
        @index[word] = [] if @index[word].nil?
        @index[word].push(obj)
      end
    end
  end

  def lookup(word)
    @index[word.downcase]
  end

end

class MyLogger

  private_class_method :new

  @@logger = nil

  def MyLogger.create
    @@logger = new unless @@logger
    @@logger
  end

end

class Button

  def initialize(label)
    @label = label
  end

end

songlist = SongList.new

class JukeboxButton < Button

  def initialize(label, &action)
    super(label)
    @action = action
  end

  def button_pressed
    @action.call(self)
  end

end

start_button = JukeboxButton.new("Start") { songlist.start }
pause_button = JukeboxButton.new("Pause") { songlist.pause }


require 'test/unit'
class TestSongList < Test::Unit::TestCase

  def test_delete
    list = SongList.new
    s1 = Song.new('title1', 'artst1', 1)
    s2 = Song.new('title2', 'artst2', 2)
    s3 = Song.new('title3', 'artst3', 3)
    s4 = Song.new('title4', 'artst4', 4)
    list.append(s1).append(s2).append(s3).append(s4)
    assert_equal(s1, list[0])
    assert_equal(s3, list[2])
    assert_nil(list[9])
    assert_equal(s1, list.delete_first)
    assert_equal(s2, list.delete_first)
    assert_equal(s4, list.delete_last)
    assert_equal(s3, list.delete_last)
    assert_nil(list.delete_last)
  end

end

Answer 1

You don’t have getters and setters for name. e.g.

def name
 @name
end

def name=(name)
 @name = name
end

Do that for all the attributes you want to set explicitly and not through the initializer. There is a shortcut. attr_accessor. Read: http://www.rubyist.net/~slagell/ruby/accessors.html