Complete file for blog entry "The Complete Class"

album.rb

require 'yaml'

Track = Struct.new :title, :duration

# An Album represents an audio medium which has title,
# interpret, a pause duration between tracks and a list
# of individual tracks.
class Album
  attr_reader :title, :interpret, :pause

  # initialization

  def initialize(title, interpret, pause = 0)
    super()

    # main properties
    self.title = title
    self.interpret = interpret
    @tracks = []

    # additional properties
    self.pause = pause

    # redundant properties
    # left out
  end

  def title=(t)
    @title = t.dup.freeze
  end

  def interpret=(i)
    @interpret = i.dup.freeze
  end

  def pause=(time)
    @pause = time
    @duration = nil
  end

  def each_track(&b)
    @tracks.each(&b)
    self
  end

  def add_track(tr)
    @tracks << tr
    @duration = nil
    self
  end

  def clear_tracks
    @tracks.clear
    @duration = nil
    self
  end

  alias << add_track

  def tracks
    @tracks.dup
  end

  def duration
    @duration ||= @tracks.empty? ?
      0 :
      @tracks.inject(-pause) do |sum, tr|
        sum + pause + tr.duration
      end
  end

  # conversion to a printable string

  def to_s
    "Album '#{title}' by '#{interpret}' (#{tracks.size} tracks)"
  end

  # equivalence

  def eql?(album)
    self.class.equal?(album.class) &&
      title == album.title &&
      interpret == album.interpret &&
      tracks == album.tracks
  end

  alias == eql?

  # hash code calculation

  def hash
    title.hash ^
      interpret.hash ^
      tracks.hash
  end

  # comparability

  include Comparable

  def <=>(o)
    self.class == o.class ?
      (interpret <=> o.interpret).nonzero? ||
      (title <=> o.title).nonzero? ||
      (tracks <=> o.tracks).nonzero? ||
      (pause <=> o.pause) || 
      0 :
      nil
  end

  # cloning

  def initialize_copy(source)
    super
    @tracks = @tracks.dup
  end

  # freezing

  def freeze
    # unless frozen?
      @tracks.freeze 
      duration
    # end
    super
  end

  # customized persistence

  def marshal_dump
    a = (super rescue [])
    a.push(@title, @interpret, @pause, @tracks)
  end

  def marshal_load(dumped)
    super rescue nil
    @title, @interpret, @pause, @tracks = *dumped.shift(4)
  end

  def to_yaml_properties
    a = super
    a.delete :@duration
    a
  end

  # matching

  def ===(track)
    t = (track.title rescue track)
    tracks.find {|tr| t == tr.title}
  end

  def =~(rx)
    rx =~ title
  end

end

# ===== Test Code ===================================================

alb = Album.new "In through the out door", "Led Zeppelin", 2
printf "%-30s %p\n", 'empty album', alb

alb << Track.new("In the Evening", 6 * 60 + 49)
alb << Track.new("South Bound Saurez", 4 * 60 + 12)
alb << Track.new("Fool in the Rain", 6 * 60 + 12)
alb << Track.new("Hot Dog", 3 * 60 + 17)

printf "%-30s %p\n", 'page 1 completed', alb
printf "%-30s %p\n", 'duration', alb.duration
printf "%-30s %p\n", 'after duration calculation', alb

page1 = alb.dup
printf "%-30s %p\n", 'copy of page 1', page1
printf "%-30s %p\n", 'copy equivalent?', alb == page1
printf "%-30s %p\n", 'really?', page1 == alb

alb << Track.new("Carouselambra", 10 * 60 + 32)
alb << Track.new("All my Love", 5 * 60 + 51)
alb << Track.new("I'm gonna crawl", 5 * 60 + 30)

alb.duration

printf "%-30s %p\n", 'full album', alb
printf "%-30s %p\n", 'page 1', page1

printf "%-30s %p\n", 'track found?', alb === "All my Love"
printf "%-30s %p\n", 'track on page 1', page1 === "All my Love"

puts alb, page1

2.times { alb.freeze }

printf "%-30s %p\n", 'full album', alb

alb2 = Marshal.load(Marshal.dump(alb))
printf "%-30s %p\n", 'marshaled', alb2

alb3 = YAML.load(YAML.dump(alb))
printf "%-30s %p\n", 'yamld', alb3
printf "%-30s %p\n", 'yamld duration', alb3.duration