From: "Abinoam Jr." <abinoam@...>
Date: 2011-01-18T09:24:53+09:00
Subject: Re: Calling by Reference - Two Questions

I think I didn't understand your question correctly, sorry (My english
skills are not so good).
But, see bellow and tell me if this is what you want.

def myswap(arr)
  [arr[1], arr[0]]
end

def myswap!(arr)
  arr[0], arr[1] = arr[1], arr[0]
end

def myswap2!(arr)
  arr[0], arr[1] = arr[1], arr[0]
  arr
end

a = [2, 5]

myswap a # => [5,2] (new object)
myswap! a # => [5,2] (a now is changed; note that the returned array is not a)
myswap2! a # => [5,2] (a now is changed; the returned array is "a"
(same object_id) )

Abinoam Jr.

On Mon, Jan 17, 2011 at 9:07 PM, Mike Stephens <rubfor@recitel.net> wrote:
> I know I'm not the first person to get stumped by how to get Ruby to
> change an object in a method.
>
> I want to do:
>
> method a1 or a1.method
>
> I can do
>
>  a1 = method a1
>
> but amongst other things that creates a new object.
>
> a1 = [1,2]
> puts " #{a1} # 12
>
> def myswap1(a2)
>  a3 = [0,0]
>  a3[0] = a2[1]
>  a3[1] = a2[0]
>  a2 = a3
>  end
>
> myswap1 a1
> puts " #{a1} " # 12
>
> Ruby passes in a1, so at the start of the method a2 is the same
> reference as a1. However when I assign a1 = a3, a1 becomes a different
> reference and disappears when the method terminates.
>
> So my first question is why won't Ruby let me do this:
>
> a1 = [1,2]
>
> public
> def myswap5
>  a3 = [0,0]
>  a3[0] = self[1]
>  a3[1] = self[0]
>  self = a3
>  end
>
> a1.myswap5 # gives error message: Can't change the value of self
>
> My second question is from this:
>
> a1 = [1,2]
>
> def myswap6(a2)
>  a2.reverse!
>  end
>
>  myswap6 a1
>  puts " #{a1}" #21
>
> What magic is reverse! using, and how can I avail myself of it?
>
> --
> Posted via http://www.ruby-forum.com/.
>
>