From: Justin Collins <justincollins@...>
Date: 2008-12-30T16:21:18+09:00
Subject: [ruby-core:20986] Re: [Feature #929] Array#shuffle does not initialize random seed

Kurt Stephens wrote:
> Not a bug; it's a feature?  The best thing about pseudorandom generators *is*
> that they are not random. :)
>
> Justin Collins wrote:
>   
>> Feature #929: Array#shuffle does not initialize random seed
>> http://redmine.ruby-lang.org/issues/show/929
>>
>> Author: Justin Collins
>> Status: Open, Priority: Low
>> Category: core, Target version: 1.9.1 Release Candidate
>>
>> Unlike calling Kernel#rand, Array#shuffle and Array#shuffle! do not automatically seed the random number generator. This means subsequent runs of the same program will produce the same shuffles unless a separate call is made to Kernel#rand or Kernel#srand.
>>
>> For example, running just
>>
>> ruby -e 'p Array.new(50) {|n| n }.shuffle'
>>
>> will always give the same output.
>>
>>
>> ----------------------------------------
>> http://redmine.ruby-lang.org
>>
>>     

Well, both behaviors are available, it is just a matter of which one is 
more convenient.
Apparently this has already been changed (my mistake, I did not see the 
revision anywhere), but I would argue (if I had to) that one would 
usually desire subsequent runs of the program to produce different, 
pseudorandom results. On the less common (in my opinion) occasion, when 
a specific starting seed is required, then one can use srand(seed) 
first. This is also consistent with the behavior of Kernel#rand.

-Justin