Re: the behavior of iterator methods

So you can accomplish what you want like so.

a = [1, 2, 3]
a.each_with_index { |x, index| a[index] += 1 }
puts a

Or

(0...a.length).each { |x| a[x] += 1 }

On Wednesday, September 19, 2012, Jam Bees wrote:

> Some methods change objects in place, others return a changed object and
> leave the original in place.
>
>  The bang is placed by convention at the end of methods that have some
> unusual behavior; most often, this unusual behavior is that a data
> structure is passed in by reference not by value.
>
> On Sep 19, 2012, at 9:32 PM, ten ten <[e-mail] <javascript:;>>
> wrote:
>
> > Hi all,
> >
> > Sorry, I deleted my previous post on the ruby forum by mistake.
> > So I post it again.
> >
> >
> >
> > I am a Ruby-beginner.
> > I have some experience of C/C++ for several years.
> > It has been only one week since I started to learn Ruby.
> > Please tell me about the behavior of iterator methods.
> >
> > At first, I did as bellow on the irb environment.
> > -------------------------------------------------------
> > irb(main):001:0> s = ["a", "b", "c"]
> > => ["a", "b", "c"]
> > irb(main):002:0> s[0].object_id
> > => 36971304
> > irb(main):003:0> s[1].object_id
> > => 36971292
> > irb(main):004:0> s[2].object_id
> > => 36971280
> > irb(main):005:0> s.each{|c| c.upcase!}
> > => ["A", "B", "C"]
> > irb(main):006:0> p s
> > ["A", "B", "C"]
> > => nil
> > -------------------------------------------------------
> >
> > Looking at this, I thought I can change the value of each element in
> > Array object through iterator methods.
> >
> > However, when I did next as bellow, that behavior looked different.
> > -------------------------------------------------------
> > irb(main):007:0> a = [1,2,3]
> > => [1, 2, 3]
> > irb(main):008:0> a[0].object_id
> > => 3
> > irb(main):009:0> a[1].object_id
> > => 5
> > irb(main):010:0> a[2].object_id
> > => 7
> > irb(main):011:0> a.each{|i| i += 1}
> > => [1, 2, 3]
> > irb(main):012:0> p a
> > [1, 2, 3]
> > => nil
> >
> > irb(main):013:0> a.each{|i| p i.object_id}
> > 3
> > 5
> > 7
> > => [1, 2, 3]
> > -------------------------------------------------------
> >
> > I expected that Array#each method with the code block would change
> > contents of the Array object variable named 'a' into [2,3,4].
> > But it didn't. Why?
> >
> > The object IDs of a[0], a[1], a[2] are shown through
> > the the code block of Array#each. So I thought if variable named 'i'
> > changed its value, that had to be reflected to the Array object 'a'.
> > But it didn't.
> >
> >
> > Why did this difference happened?
> >
> > --
> > Posted via http://www.ruby-forum.com/.
> >
>
>

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