Noob question, regarding array

ruby-talk
1

I'm a noob, trying to learn ruby.
I'm following along with the book Programming Ruby, The Pragmatic
Programmer's Guide, which comes with ruby documentation.

Im on chapter, Implementing a SongList Container, doing the code
samples, but i'm getting the following error when trying to run the
code:
18:in `append': undefined method `push' for nil:NilClass
(NoMethodError)
  from F:/InstantRails/rails_apps/test/test2.rb:80

I have a SongList class with the following method:

  def append(aSong)
    @songs.push(aSong)
    self
  end

and im trying to run the code sample as in the book:

list = SongList.new
list.
  append(Song.new('title1', 'artist1', 1)).
  append(Song.new('title2', 'artist2', 2)).
  append(Song.new('title3', 'artist3', 3)).
  append(Song.new('title4', 'artist4', 4))

This doesnt make any sense. I can create the Song object just fine,
but if i try to add it to the array i get this erro.
Can anyone help me please?

2

You did not show all the code but my guess would be that you did not initialize @songs properly in #initialize.

Kind regards

  robert

···

On 13.06.2009 11:36, Thiago wrote:

Im on chapter, Implementing a SongList Container, doing the code
samples, but i'm getting the following error when trying to run the
code:
18:in `append': undefined method `push' for nil:NilClass
(NoMethodError)
  from F:/InstantRails/rails_apps/test/test2.rb:80

I have a SongList class with the following method:

  def append(aSong)
    @songs.push(aSong)
    self
  end

and im trying to run the code sample as in the book:

list = SongList.new
list.
  append(Song.new('title1', 'artist1', 1)).
  append(Song.new('title2', 'artist2', 2)).
  append(Song.new('title3', 'artist3', 3)).
  append(Song.new('title4', 'artist4', 4))

This doesnt make any sense. I can create the Song object just fine,
but if i try to add it to the array i get this erro.
Can anyone help me please?

--
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/

3

What do you have in the initialize method of the SongList class? From the
error message you get, it seems that @songs is nil instead of being an array.
To avoid this, you need to set the @songs instance variable to an array and
usually this is done in the initialize method. It should be something like
this:

class SongList

  def initialize
    #other initialization code can go here
    @songs =
    #other initialization code can go here
  end

end

I hope this helps

Stefano

···

On Saturday 13 June 2009, Thiago wrote:

>I'm a noob, trying to learn ruby.
>I'm following along with the book Programming Ruby, The Pragmatic
>Programmer's Guide, which comes with ruby documentation.
>
>Im on chapter, Implementing a SongList Container, doing the code
>samples, but i'm getting the following error when trying to run the
>code:
>18:in `append': undefined method `push' for nil:NilClass
>(NoMethodError)
> from F:/InstantRails/rails_apps/test/test2.rb:80
>
>I have a SongList class with the following method:
>
> def append(aSong)
> @songs.push(aSong)
> self
> end
>
>and im trying to run the code sample as in the book:
>
>list = SongList.new
>list.
> append(Song.new('title1', 'artist1', 1)).
> append(Song.new('title2', 'artist2', 2)).
> append(Song.new('title3', 'artist3', 3)).
> append(Song.new('title4', 'artist4', 4))
>
>This doesnt make any sense. I can create the Song object just fine,
>but if i try to add it to the array i get this erro.
>Can anyone help me please?

4

yes that was the problem.I just typed initialize incorrectly, so my array was not being initialized.I should've got a decent ide to avoid this stupid mistakes.
Thanks

···

Date: Sat, 13 Jun 2009 18:54:10 +0900
From: stefano.crocco@alice.it
Subject: Re: Noob question, regarding array
To: ruby-talk@ruby-lang.org

On Saturday 13 June 2009, Thiago wrote:
> >I'm a noob, trying to learn ruby.
> >I'm following along with the book Programming Ruby, The Pragmatic
> >Programmer's Guide, which comes with ruby documentation.
> >
> >Im on chapter, Implementing a SongList Container, doing the code
> >samples, but i'm getting the following error when trying to run the
> >code:
> >18:in `append': undefined method `push' for nil:NilClass
> >(NoMethodError)
> > from F:/InstantRails/rails_apps/test/test2.rb:80
> >
> >I have a SongList class with the following method:
> >
> > def append(aSong)
> > @songs.push(aSong)
> > self
> > end
> >
> >and im trying to run the code sample as in the book:
> >
> >list = SongList.new
> >list.
> > append(Song.new('title1', 'artist1', 1)).
> > append(Song.new('title2', 'artist2', 2)).
> > append(Song.new('title3', 'artist3', 3)).
> > append(Song.new('title4', 'artist4', 4))
> >
> >This doesnt make any sense. I can create the Song object just fine,
> >but if i try to add it to the array i get this erro.
> >Can anyone help me please?

What do you have in the initialize method of the SongList class? From the
error message you get, it seems that @songs is nil instead of being an array.
To avoid this, you need to set the @songs instance variable to an array and
usually this is done in the initialize method. It should be something like
this:

class SongList

  def initialize
    #other initialization code can go here
    @songs =
    #other initialization code can go here
  end

end

I hope this helps

Stefano

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