From: Josh Cheek <josh.cheek@...>
Date: 2009-12-29T15:20:54+09:00
Subject: Re: PLEASE HELP...dup is not working correctly in the following code

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On Mon, Dec 28, 2009 at 11:40 PM, timr <timrandg@gmail.com> wrote:

> #dup creates a copy of an object with a different object_id. As
> follows:
> >> a = [1,2,3]
> => [1, 2, 3]
> >> b = a.dup
> => [1, 2, 3]
> >> b << 1000
> => [1, 2, 3, 1000]
> >> a
> => [1, 2, 3]
> >>  b
> => [1, 2, 3, 1000]
>
>

This is the difference

$ irb
>> a = [ 'w' , 'x' , 'y' ]
=> ["w", "x", "y"]

>> b = a.dup
=> ["w", "x", "y"]

>> a << 'z'
=> ["w", "x", "y", "z"]

>> b
=> ["w", "x", "y"]

>> a[0] << 'x'
=> "wx"

>> a
=> ["wx", "x", "y", "z"]

>> b
=> ["wx", "x", "y"]


a and b are different arrays, but they each contain the same objects.

I think the only way to make a deep copy is to explicitly dup everything in
the array also, or to use marshall. I'm not sure why there isn't a deep copy
method.

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