From: "David A. Black" <dblack@...>
Date: 2005-01-19T10:38:47+09:00
Subject: Re: value by reference

Hi --

On Wed, 19 Jan 2005, Mohammad Khan wrote:

> Before telling my issue, let me show my script:
>
>
> def do_something(a, b, c)
>    a = a + 1
>    b = b + 2
>    c = c + 3
> end
> a, b, c = 5, 6, 7
>                                                                                                                                                        puts "before do_something:"
> puts "a : #{a}"
> puts "b : #{b}"
> puts "c : #{c}"
>                                                                                                                                                             do_something(a, b, c)
>                                                                                                                                                            puts "after do_something:"
> puts "a : #{a}"
> puts "b : #{b}"
> puts "c : #{c}"
>
>
>
> My issue:
> I would like to see the value of a, b, c after calling #do_something as:
> a = 6, b = 8, c = 10
>
> how can I do it without making a, b, c an instance variable?
> In other words, how can I send value by reference?

Fixnums are immediate values, and are immutable, even when they're
wrapped in variables.  So what you're trying to do is equivalent to:

   do_something(5,6,7)

   puts 5 * 5   # 36 -- i.e., 5 has become 6

It won't work (luckily :-) because Ruby doesn't let you perform that
kind of modification on Fixnums.

With mutable objects you can do what you're describing -- for example,
adding to a string that's in a local variable:

   irb(main):001:0> def x(y); y << "def"; end
   => nil
   irb(main):002:0> s = "abc"
   => "abc"
   irb(main):003:0> x(s)
   => "abcdef"
   irb(main):004:0> s
   => "abcdef"


David

-- 
David A. Black
dblack@wobblini.net