From: "jan aerts (RI)" <jan.aerts@...>
Date: 2006-11-14T00:40:07+09:00
Subject: Re: classes within classes

> -----Original Message-----
> From: Jan Svitok [mailto:jan.svitok@gmail.com] 
> Sent: 13 November 2006 15:03
> To: ruby-talk ML
> Subject: Re: classes within classes
> 
> >
> >  +----------------------------picture-+
> >  | +----------------------track1----+ |
> >  | |                                | |
> >  | |  x          x                  | |
> >  | |         x               x      | |
> >  | |                                | |
> >  | |                                | |
> >  | +--------------------------------+ |
> >  |                                    |
> >  | +----------------------track2----+ |
> >  | |                                | |
> >  | |                     xx         | |
> >  | +--------------------------------+ |  
> > +------------------------------------+
> >
> > <SNIP>
> >
> > More elaborately (showing some of the key features) <LIB 
> CODE SNIPPET>  
> > class Picture
> >    def initialize(width)
> >      @width = width
> >      @tracks = Array.new
> >    end
> >    attr_accessor :width, :tracks
> >
> >    def add_track(name)
> >      @tracks.push(Picture::Track.new(name)
> >      return @tracks[-1]
> >    end
> >
> >    class Track
> >      # DO NOT CALL INITIALIZE METHOD DIRECTLY: use Picture#add_track
> >      def initialize(name)
> >        @name = name
> >      end
> >      attr_accessor :name
> >
> >      def to_svg
> >        # I NEED THE WIDTH OF THE PICTURE HERE
> >        return
> > some_xml_that_includes_the_width_which_was_defined_in_Picture
> >      end
> >
> >      class Feature
> >        ...
> >      end
> >    end
> >  end
> > </LIB CODE SNIPPET>
> >
> > <USAGE SNIPPET>
> > p = Picture.new(800)  # Creates a new picture of 800pt width.
> > p.add_track('first_track')
> > p.add_track('second_track')
> > </USAGE SNIPPET>
> >
> > In the end, the question is: should I make Picture#width a global 
> > variable, should I add width as an argument to 
> > Picture::Track#initialize, or is there a more elegant solution? (I 
> > hope it's the last one...)
> >
> > Any help would be very much appreciated, jan.
> 
> Hi,
> 
> two ideas:
> 1. pass the picture (it)self to the Track constructor and 
> then query whatever you need 2. have all the svg generating 
> stuff in another class that will be given the Picture object, 
> and will iterate through it, creating the xml along the way 
> (ERB template comes to my mind...)
> 
> Jan
> 
> 
Thanks for your swift reply, Jan.

I did look briefly at these two options, but didn't go for them
previously. However, passing the Picture object itself _might_ actually
be the best solution. I suppose the code would then look something like:

class Picture
  def add_track(self, name)
    @tracks.push(Picture::Track.new(self, name))
  end

  class Track
    def initialize(picture, name)
      width = picture.width
      name = name
    end
  end
end

I'll probably go for this one...

jan.