From: Todd Benson <caduceass@...>
Date: 2009-04-27T14:05:13+09:00
Subject: Re: How to parse a "line"?

On Sun, Apr 26, 2009 at 11:45 PM, 7stud -- <bbxx789_05ss@yahoo.com> wrote:
> Todd Benson wrote:
>> On Sun, Apr 26, 2009 at 11:03 PM, Todd Benson <caduceass@gmail.com>
>> wrote:
>>> to me if it did.
>> Let me rephrase.  What is different on the underlying structure with
>> [1..-1] and #shift?  I'm not sure if shift really moves everything,
>> but if it does, I wouldn't mind knowing.
>>
>> Todd
>
> shift changes the array in place:

I looked at an old thread where Bob Hutchinson piped in about
potential GC problems with this, but that was back in '07

>
> 1)
> arr = [10, 20, 30]
>
> y = arr.shift
> puts y
> p arr
>
> --output:--
> 10
> [20, 30]
>
>
> subscripts create a new array:
>
> 2)
> arr = [10, 20, 30]
> p arr
> print "id: ", arr.object_id
> puts
>
> x = arr[1..-1]

new object is created by x =

> p x
> print "id: ", x.object_id
> puts
> p arr
>
> --output:--
> [10, 20, 30]
> id: 75950
> [20, 30]
> id: 75860
> [10, 20, 30]
>
>> Is that really what happens?  I thought it just reassigned a starting
>> point, and indexed from there.  At least, that would make more sense
>> to me if it did.
>
> Would it?  What if you had an array that took up 3GB of memory and you
> shifted off every element but the last one.  Would you expect your array
> to still occupy 3GB of memory?

I would hope that the GC could keep up, and I'd plan accordingly if
not.  But if your 3GB array was duped/cloned, hmm, is that better?
Please tell me we are talking about two different arguments.

Todd