From: Robert Klemme <bob.news@...>
Date: 2003-05-21T17:56:37+09:00
Subject: Re: Copying an Array


You want a deep copy of a nested array structure.  As easy as that:

module Enumerable
  def deep_copy
    map {|x| x.respond_to?( :deep_copy ) ? x.deep_copy : x}
  end
end

a=[[1,2],[3,4]]

b=a.dup
puts( a.equal?( b ) )
puts( a[0].equal?( b[0] ) )

b=a.deep_copy
puts( a.equal?( b ) )
puts( a[0].equal?( b[0] ) )

Yields:

false
true
false
false

Regards

    robert

"Frederic Chalons - Design Support IA Student" <frederic.chalons@st.com>
schrieb im Newsbeitrag news:3ECB3715.7000204@st.com...
> 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.
>
> Btw, a would be modified even though it is accessed as attri_reader. So
>  I guess  =  is copying the pointer rather than any content (a.id ==
b.id)
>
> (using ruby 1.6.8 (2002-12-24) [sparc-solaris2.8])
>
> Thank you,
> Fred
>
>