From: Tomasz Wegrzanowski <taw@...>
Date: 2002-01-05T11:52:49+09:00
Subject: [ruby-talk:30262] Re: self being altered even when .dup'ed

On Sat, Jan 05, 2002 at 11:41:08AM +0900, dempsejn@georgetown.edu wrote:
> Hey All,
> 
> I've just narrowed down something that was bugging me, and I think I'm 
> realizing that its a feature, not a bug or error.
> I'm extending chomp to take an array. here's the code:
> 
> class Array
>  def tester
>     v = self.dup
>     p self
>     p v
>     v[0] = v[0].chomp
>     v[1].chomp!
>     p self
>     p v    
>   end
> 
> end
> 
> If you run that with:
> 
> a = ["str1\n","str2\n"]
> a.tester
> 
> you'll see:
> 
> ["str1\n", "str2\n"]
> ["str1\n", "str2\n"]
> ["str1\n", "str2"]
> ["str1", "str2"]
> 
> As I'd expect, the newline is gone from v[0] and v[1], but what bugs me 
> is that its gone from self[1] as well...its clearly the chomp! call, 
> but i'm a little confused...i thought .dup would make a copy that i'd 
> play with leaving the original self alone...it would make sense to me 
> if i did v = self, but i thought that's where the dupe would solve my 
> problem...i could code the above slightly differently (using a simple 
> chomp instead of chomp!) to get around this behavior, but i wanted to 
> try and understand why its happening...
> thanks!
> Jack

dup makes shallow copy - only array is copied, not it's contents.
Array in Ruby contains variables (==pointers), not objects.