From: Rick DeNatale <rick.denatale@...>
Date: 2009-03-14T23:44:11+09:00
Subject: Re: How do arrays in Ruby work?

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On Sat, Mar 14, 2009 at 10:12 AM, Peter Wu <pwu.380@gmail.com> wrote:

> As in how they are organized behind the scenes.
>
> For example, if I say
>
> arr = [1, 2, 3, 4]
> arr.slice[1]


I think you meant either

  arr.slice(1)
or
  arr[1]

arr.slice[1] won't work since slice requires arguments, and this is being
interpreted as
  (arr.slice)[1]

>
>
> Is it going to have to physically relocate everything after 2 in memory?
> Would using a linked list be more efficient if a lot of elements are
> going to be removed and inserted?



So far we haven't done anything which would add or remove anything

arr.slice(1)  simply returns a reference to the object in the second element
of arr.  arr is untouched

arr.slice(1,3) would return an array containing the second, third and fourth
elements, the original array would be untouched. AND

The MRI ruby implementation of arrays uses a copy on write scheme, so that
both arr and the returned object would actually share memory for the array
of references.  If one or the other changed then a copy would be triggered.

Ruby arrays are implemented rather efficiently both in terms of space and
speed. It's usually best to use them simply and only worry about performance
issues when they arise, and when they do, it will probably be something
other than "I should have used a linked list instead of an array"


-- 
Rick DeNatale

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