From: Rob Biedenharn <Rob@...>
Date: 2010-09-23T04:43:23+09:00
Subject: Re: Odd behavior when << hash

On Sep 22, 2010, at 3:33 PM, Alex Stahl wrote:

> Hi Folks - Using Ruby 1.8.7, I found this oddity:
>
> require 'rubygems'
> require 'json'
>
> setup = []
> ids = ["12345", "54321", "21345", "548752", "3215", "50203"]
>
> doIt = {
>  "action" => "do something",
>  "result" => "true"
> }
>

# so here, doIt is referencing an object which is a hash

> cnt = rand(10)
> 1.upto(cnt) do
>
>  doIt['params'] = ids[rand(6)]
>  p "Pushing step: #{doIt.inspect}"
>  setup << doIt

# this puts that reference into the setup array
# NOTE: it is always referring to the same hash

> end
>
> p "Final steps list: #{setup.inspect}"
>
> **************************************
>
> When I inspect my final steps list at the end, the values of
> 'doIt['params']' is always the same - set to the last value of the  
> last
> run of the upto loop.  But when I inspect doIt prior to pushing it, I
> can see that it has its own value, acquired randomly.
>
> So my question is, why is the hash not being pushed onto the array
> properly?  What side effect am I encountering here and how do I get
> around it?
>
> (I've already tried declaring "params" => "" in the initial hash
> creation; that didn't help).
>
> Thanks,
> Alex
>
> PS - You'd be correct in noting this code doesn't do anything useful.
> I've stripped away other parts to isolate the questionable behavior  
> for
> demonstration purposes.
>
>


Try creating the hash object inside the loop (i.e., creating a new  
object each time)

rand(10).times do
  setup << { "action" => "do something",
             "result" => "true",
             "params" => ids[rand(6)].dup
           }
end
puts "Final steps list: #{setup.inspect}"


Note that I'm also calling .dup on the element taken from the ids  
array so there's a separate string object.  You can apply this to your  
real code, I hope.

-Rob

Rob Biedenharn		
Rob@AgileConsultingLLC.com	http://AgileConsultingLLC.com/
rab@GaslightSoftware.com		http://GaslightSoftware.com/