Ruby | attr_accessor + initialize でアクセサ変数に代入できない時 ref: http://qiita.com/Yinaura/items/02c8bd7bd87cfa64ce6c

file0.txt

class Book
  attr_accessor :price

  def initialize
    price = 1080
  end
end

file1.txt

book = Book.new
p book.price

# => nil

file2.txt

class Book
  attr_accessor :price

  def initialize
    self.price = 1080
  end
end

file3.txt

book = Book.new
p book.price

# => 1080