From: Gary Wright <gwtmp01@...>
Date: 2011-01-18T12:34:48+09:00
Subject: Re: Calling by Reference - Two Questions


On Jan 17, 2011, at 10:05 PM, Mike Stephens wrote:

> Well, that is bizarre.
> 
> In 1.8.6 I get:
> 
> def myswap(arr)
>  [arr[1], arr[0]]
> end
> 
> def myswap!(arr)
>  arr[0], arr[1] = arr[1], arr[0]
> end
> 
> def myswap2!(arr)
>  arr[0], arr[1] = arr[1], arr[0]
>  arr
> end
> 
> a = [2, 5]
> puts " start #{a} #{a.object_id} " #start 25 27431650
> 
> myswap a # => [5,2] (new object)
> puts " myswap #{a} #{a.object_id} " myswap 25 27431650
> 
> myswap! a # => [5,2] (a now is changed; note that the returned array
> isnot a)
> puts " myswap! #{a} #{a.object_id} " myswap! 52 27431650
> 
> myswap2! a
> puts " myswap2! #{a} #{a.object_id} " myswap2! 25 27431650
> 
> 
> I have no idea why myswap! works and myswap2! doesn't.


They both work.  Remember that myswap!(a) changed the array to [5,2] and so myswap2! changes it back to [2,5].

Gary Wright