From: timr <timrandg@...>
Date: 2009-12-29T15:45:06+09:00
Subject: Re: PLEASE HELP...dup is not working correctly in the following code

On Dec 28, 10:20 pm, Seebs <usenet-nos...@seebs.net> wrote:
> On 2009-12-29, timr <timra...@gmail.com> wrote:
>
> > You are right about the strings having the same object_ids in each
> > object, which explains why the modification on the dupped object
> > affects the original strings. That helps. But the suggested strategy
> > doesn't solve the problem:
>
> Hmm.
>
> >>> a = [['a', 'b'], ['c','d']]
> >=> [["a", "b"], ["c", "d"]]
> >>> a.each{|r| r.each{|letter| p letter.object_id}}
> > 4442750
> > 4442740
> > 4442710
> > 4442700
> >=> [["a", "b"], ["c", "d"]]
> >>> b = a.map{|r| r.each{|letter| letter.dup}}
>
> This doesn't seem right.  The inner loop (which is the one I think
> we care about) is using each, not map.  So we never actually return
> the array consisting of all the duplicated letters.
>
> If you have an array of arrays, I think you need to use map at both
> levels.
>
> irb(main):001:0> a = [['a', 'b'], ['c','d']]
> => [["a", "b"], ["c", "d"]]
> irb(main):002:0> b = a.map {|r| r.map{|l| l.dup}}
> => [["a", "b"], ["c", "d"]]
> irb(main):003:0> a.each{|r| r.each{|letter| p letter.object_id}}
> 2152912244
> 2152912216
> 2152912132
> 2152912104
> => [["a", "b"], ["c", "d"]]
> irb(main):004:0> b.each{|r| r.each{|letter| p letter.object_id}}
> 2152886456
> 2152886316
> 2152886232
> 2152886176
> => [["a", "b"], ["c", "d"]]
>
> What's throwing you off here is that .each returns the array object
> it started with.
>
> So "r.each {...}" always returns r, unmodified.
>
> -s
> --
> Copyright 2009, all wrongs reversed.  Peter Seebach / usenet-nos...@seebs.nethttp://www.seebs.net/log/<-- lawsuits, religion, and funny pictureshttp://en.wikipedia.org/wiki/Fair_Game_(Scientology) <-- get educated!

I was just going to post that correction after I realized that
mistake. Thanks for the help.