From: Michael Neumann <mneumann@...>
Date: 2003-05-21T17:59:15+09:00
Subject: Re: Copying an Array

On Wed, May 21, 2003 at 05:24:13PM +0900, Frederic Chalons - Design Support IA Student wrote:
> Hi,
> 
> The = operator seems to retrieve an reference on a Array rather than 
> copying what it contains
> as in the following code:
> *******
> a = [1,2,3]
> b = a
> 
> p b.id; p a.id
> b.each_index do |i|
>  b[i] *= 2
> end
> ********
> both a and b equals to [2,4,6]
> 
> This can be solve by using a.collect or a.dup but the problem would 
> occur again if a,b are multi dimensions Array. dup or collect reference 
> on the sub-Array?
> Isn't there a clean and consise way to copy the whole content of an 
> multi dimension Array so that the copy is not somehow linked to the 
> original.

Use Marshal:

def deep_clone(anObj)
  Marshal.load(Marshal.dump(anObj))
end

> Btw, a would be modified even though it is accessed as attri_reader. 

You can modify the arrays content, but you cannot assign a new object to
a (@a).

> So I guess  =  is copying the pointer rather than any content (a.id == b.id)

= is just a reference assignment, does not copy anything except the
pointer at all.

Note that []= or obj.a= are methods and not an assignment! 
  
  a = [1,2,3]
  a[0] = 2     # This is no assignment! It's a method call!


Regards,

  Michael