From: Chris Moline <ugly-daemon@...>
Date: 2001-07-24T04:11:57+09:00
Subject: [ruby-talk:18371] Re: Newbie question: Data structures in Ruby.

On Tue, Jul 24, 2001 at 01:26:34AM +0900, Erik wrote:
> Pierre-Charles David wrote:
> 
> > > In the end, the page should contain a list of articles, and each article
> > > a list of elements.
> > > I want to have acces to it like:
> > >
> > > puts currentpage.articles[2].elements[5].content
> > >
> > > I want to be able to manipulate this data structure like f.i.:
> > >
> > > currentpage.articles[2].elements[5].content = 'Hello world'
> > >
> > > I am not sure if or how I can realise this, could somebody please give
> > > me a hint?
> >
> > Ruby makes attributes hidden ('private') by default. You need to
> > explicitely define reader methods for those you want to make accessible:
> 
> Okay, so now I have
> 
> class Page
>     attr_writer :articles
>     def initialize
>         @articles = []
>     end
>     ...
> end
> 
> class Article
>     attr_writer :elements
>     def initialize
>         @elements = []
>     end
>     ...
> end
> 
> class Element
>     attr_writer :content
>     ...
> end
> 
> But how do I go from here?
> The following does not work:
> 
> currentpage = Page.new
> currentpage.articles.push(Article.new)
> 
> I get a 'undefined method: articles' error.
> 
> Regards,
> 
>     Erik.
You need to use attr_accesor instead of attr_writer because attr_writer only
creates the articles= method while attr_accessor creates both articles= and
articles. To get the subscripting thing going you need to redefine []. ie

class Article
	def initialize
		@arr = [1, 2, 3]
	end

	def [](i)
		@arr[i]
	end
end

article = Article.new
p article
print article[1], "\n"
print article[0], "\n"
print article[2], "\n"

Hope this helps,
Chris Moline