From: Alex Stahl <astahl@...5.com>
Date: 2010-09-23T04:51:54+09:00
Subject: Re: Odd behavior when << hash

Thanks, Rob.  Made the mistake of assuming I get a copy of the hash when
I push it.  IIRC, there are other (not-so-elegant) languages that do so.

Appreciate the point about .dup as well, but since at the end of this,
I'm just writing everything out to a file, and the elements of ids will
never change (at least not in this script), I don't think I need a
duplicate string.


On Wed, 2010-09-22 at 14:43 -0500, Rob Biedenharn wrote:
> 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/
> 
>