From: ara.t.howard@...
Date: 2006-10-13T14:06:28+09:00
Subject: Re: Any way to get lists to throw exceptions on incorrect accesses?

On Fri, 13 Oct 2006, Kenneth McDonald wrote:

> Eero Saynatkari wrote:
>> Since you asked.. :)
>> 
>> We have managed to make do without Array access raising exceptions.
>> 
>> I would REALLY recommend leaving behind the baggage of any previous
>> languages and take a head-first plunge. In Ruby, Array access returns
>> a nil if the index is not found. Embrace it! Form your code around the
>> Ruby idioms, not the other way around!
>> 
>> The payoff will be much greater.
>> 
> Certainly possible. I'm not uncomfortable with new ways of doing things (I 
> really like Ruby iteration, for example), I'm just worried this difference 
> might cause hard-to-find errors. But I just posted that as a more general 
> question, so 'nuff said here :-)


it's not that hard if you want, and you only need modify the array's you desire
- not all of them in you program:

   harp:~ > cat a.rb
   class Array
     module BoundsCheck
       def [] a, *b
         b = b.shift
         max =
           case a
           when Numeric
             a
           when Range
             a.exclude_end? ? (a.end-1) : e.end
           else
             b
           end
         raise IndexError, max.to_s if max > (size - 1)
         super
       end
     end

     def bounds_check!
       extend BoundsCheck
     end
   end

   array = %w[ 0 1 2 ]

   4.times{|i| puts "array[#{ i }] : #{ array[i].inspect }"}

   array.bounds_check!

   4.times{|i| puts "array[#{ i }] : #{ array[i].inspect }"}



   harp:~ > ruby a.rb
   array[0] : "0"
   array[1] : "1"
   array[2] : "2"
   array[3] : nil
   array[0] : "0"
   array[1] : "1"
   array[2] : "2"
   a.rb:15:in `[]': 3 (IndexError)
           from a.rb:31
           from a.rb:31


to be robust you'd want to wrap Array#slice and other 'index-y' methods.

regards.

-a
-- 
my religion is very simple.  my religion is kindness. -- the dalai lama