From: Phrogz <gavin@...>
Date: 2006-12-30T00:41:01+09:00
Subject: Re: Pickaxe book questions: Symbols and [] method

Krekna Mektek wrote:
> class SongList
>   def [](index)
>     @songs[index]
>   end
> end
>
> Why is there this [] method in the class SongList, when one is able to
> use the [] method on the songs array anyway?

This (alone) allows the consumer of the class to write code like:
  p my_song_list[ 3 ]

If you wanted to do what you suggest, you'd need to add code like:
  class SongList
    attr_reader 'songs'  # You can use strings too, if you like
  end

  p my_song_list.songs[ 3 ]

The upside of that is that you immediately get access to all the
methods of the underlying array, such as...
  my_song_list.songs.each{ |song| ... }
...which the former code (alone) doesn't make possible.

The downside, though, is that you have this class that's supposed to be
a list...and then you need to use a property of it to get at the list?
Where does the madness end? Can you imagine if your class design
required users to write code like:
  p my_song_list.songs.members.items.all[ 3 ]

I think that's the rationale behind the method you see. It shows how
you can provide a good-looking interface to your own classes.