From: "Thomas B." <tpreal@...>
Date: 2008-08-29T01:12:00+09:00
Subject: Re: Dumb "array of arrays" question

Hello Richard,

RichardOnRails wrote:
> My minor exception is that an array IS an object, so the two
> paragraphs sound weird.  He is contrasting an object of class Object
> to an object of class Array.
> 
> More importantly,  according to my tests below,  dup'ing an array does
> NOT make a new array.  It returns the (address of/pointer to) the same
> old array.

dup'ing an array DOES make a new array, only the new array looks like 
the old one, because Array#inspect doesn't return the address of the 
array so you cannot see if it is exactly the same instance or not. But 
there is a method to check it: equal?. It works like == in Java.

a=[whatever]
a.equal?(a) #=> true # the very same Array instance
a.equal?(a.dup) #=> false # it's another instance, only it looks like 
the old one when inspect'ed

But still the whatever inside a and a.dup is exactly the same thing:
a[0].euqal?(a.dup[0]) #=> true

That proves the copy is shallow - there's a new object, but it holds old 
references.

> 3: [#<Object:0x2808138>]; #<Object:0x2808138>; Array
> 4: [#<Object:0x2808138>]; #<Object:0x2808138>; Array

The [#<Object:0x2808138>]'s here are in fact different objects, only 
they look the same.

Hope that helps a bit.

T.
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