Undefined local variable error with simple program that adds items to array

Question

class Books
    attr_accessor :name, :book_id
    def initialize(name, book_id)
        @name = name,
        @book_id = book_id
    end
end

class BookCollection
    def intialize
        @book_names = []
    end

    def add_to_books(book_name)
        book_name.push(book_names)
    end
end

book1 = Books.new("catch22", "12345")
book_collection1 = BookCollection.new
book_collection1.add_to_books(book1.name)
puts book_collection1

end

That is my code and the error I'm getting is "undefined local variable or method `book_names'". I tried adding " attr_accessor :book_names" and when I do that the printed output doesn't make sense.

Don't you mean @book_names.push(book_name)? Also, instead of puts book_collection you need a method (e.g., attr_reader) to return @book_names. — Cary Swoveland
– Cary Swoveland, Commented Nov 23, 2013 at 3:35

Cary Swoveland · Accepted Answer · 2013-11-23 19:13:27Z

There are a few mistakes in your code:

line 4 should not end with a comma.
initialize in class BookCollection is misspelled, resulting in @book_names not being initialized. @book_names therefore equals nil when you attempt to add an element to it with push. nil does not have a method push; hence the exception, and the message printed with the exception.
book_name.push(book_names) should be @book_name.push(book_name). (@book_name must be an instance_variable, as opposed to a local variable, to be visible outside a method, within the class definition.
puts book_collection1 prints the class instance; you want to print @book_names.

Here I've fixed your code. I've used << instead of push. Either is OK, but the former seems to be favored my most.

class Books
  attr_accessor :name, :book_id
  def initialize(name, book_id)
  puts "name = #{name}, book_id = #{book_id}"
    @name = name
    @book_id = book_id
  end
end

class BookCollection
  attr :book_names
  def initialize
    @book_names = []
  end    
  def add_to_books(book_name)
    @book_names << book_name
  end
end

book_collection1 = BookCollection.new
book1 = Books.new("Catch22", "12345")
book2 = Books.new("Hawaii", "67890")
book_collection1.add_to_books(book1.name)
book_collection1.add_to_books(book2.name)

book_collection1.book_names # => ["Catch22", "Hawaii"]

Ismael · Accepted Answer · 2013-11-23 03:32:28Z

0

Probably just a typo at

book_name.push(book_names)

Should have been

book_names.push(book_name)

With attr_accessor :book_names

answered Nov 23, 2013 at 3:32

Ismael

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3 Comments

Cary Swoveland Over a year ago

You forgot to slap a @ on the front of book_names.

megashigger Over a year ago

I made all the changes and still get "add_to_books': undefined method push'". Btw, why is the @ necessary? I was told before that you didn't need it. @CarySwoveland

Sergio Tulentsev Over a year ago

Right, there was no attr_accessor for book_names.

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