From: Pit Capitain <pit@...>
Date: 2005-11-25T04:12:40+09:00
Subject: Re: syntax error when defining index setter []=

jchris@gmail.com schrieb:
> Thanks Yuri,
> unfortunately my problems is not as simple. If all I needed was an
> array I could write
> 
> class T
>   attr_accessor :items
>   def initialize
>     @items = []
>   end
> end
> 
> but what I need is something that acts like an array from outside of
> the class, but handles transformations to and from a more complex data
> structure "behind the scenes", ie:
> 
> class List < ActiveRecord::Base
>   has_many :middlemen
> 
>   def items
>     middlemen.collect {|middleman| middleman.item}
>   end
> 
>   def items=(new_items)
>     new_middlemen = []
>     new_items.each do |new_item|
>       new_middlemen << Middleman.create :item => new_item
>     end
>     middlemen = new_middlemen
>   end
> 
>   def items[]=(index, new_item)  #### this line gives a syntax error
>       new_middleman = Middleman.create :item => new_item
>       middlemen[index] = new_middleman
>   end
> 
> end

If you really want to have the syntax

   list.items[5] = "new"

you need to define the "[]=" method on the return value of the "items" 
method, for example (untested)

   def items
     result = middlemen.collect {|middleman| middleman.item}
     def result.[]=(index, new_item)
       new_middleman = Middleman.create :item => new_item
       middlemen[index] = new_middleman
     end
   end

Regards,
Pit