From: Robert Klemme <shortcutter@...>
Date: 2009-10-14T19:57:55+09:00
Subject: Re: deep cloning, how?

2009/10/14 Rajinder Yadav <devguy.ca@gmail.com>:
> I am trying to figure out how to perform a deep clone
>
>
> class A
>   attr_accessor :name
> end
>
> a1 = A.new
> a1.name = "yoyoma"
> a2 = a1.dup
> a1.name.chop!
> puts a2.name
>
>
> I found the following way to write a deep clone method
>
> class A
>  attr_accessor :name
>  def dup
>     Marshal::load(Marshal.dump(self))
>  end
> end
>
> If I wanted to write my own specialize deep_cloner, how would I do this. If
> I try the obvious way to do it,
>
> def dup
>   @name = self.name.dup
> end

No, this is by far not the obvious way since you would at least have
to make sure there is a copy of self and this is returned from dup.  I
would rather do

def dup
  copy = super
  copy.name = @name.dup
  copy
end

or even

def dup
  self.class.new(@name.dup)
end

Although that approach is fragile depending on the code in #initialize.

> I get an error when 'puts a2.name' is executed saying:
>
> NoMethodError: undefined method `name' for "yoyom":String
>
>
> Can someone explain what's going on when dup is called. What gets passes to
> dup (i assume self) and why my code is wrong?

Hope the above sheds some light.

Kind regards

robert

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