From: Mohammad Khan <mkhan@...>
Date: 2005-01-20T02:17:19+09:00
Subject: Re: value by reference

On Wed, 2005-01-19 at 12:05, Austin Ziegler wrote:
> On Thu, 20 Jan 2005 01:10:22 +0900, Mohammad Khan <mkhan@lextranet.com> wrote:
> > def do_something(a, b, c)
> >   a += 1
> >   b += 2
> >   c += 3
> > end
> > 
> > def another_do_something(foo = Foo.new)
> >   foo.do_something
> > end
> > 
> > class Foo
> >   def initialize
> >     @value = 0
> >   end
> > 
> >   def value
> >     return @value
> >   end
> >   
> >   def value=(val)
> >     @value = val
> >   end
> >   
> >   def do_something
> >     @value += 1
> >     @value += 2
> >     @value += 3
> >   end
> > end
> 
> > a, b, c = 5, 6, 7
> > f = Foo.new
> [...]
> > If everything is object, Why can't I do
> >   do_something(a.clone, b.clone, c.clone) # I don't want them to
> >                                           # be changed
> >   do_something(a, b, c)                   # change a, b, c like
> >                                           # other objects
> > Hope, I could explain properly what I am trying to understand.
> 
> I don't know why you're not getting this, as it is very simple.

May be I am not that simple!! :p
> 
> a, b, and c are not objects. They're variables.
Isn't everything *object* in Ruby?


Now you know, what I am after ?!

--
MOhammad


> 
> When you call Foo#do_something, you're changing the internal state
> of an object. When you call Object#do_something, you're passing
> three variables that can refer to just about any object.
> 
> It's no different than if I defined do_something as:
> 
>   def do_something(a, b, c)
>     a += Foo.new
>     b += Foo.new
>     c += Foo.new
>   end
> 
> As long as Foo can be added to the values of a, b, and c, I'm going
> to get three completely new objects.
> 
> Try it with this:
> 
>   def do_something(a, b, c)
>     a += "-half"
>     b += "-thirds"
>     c += "-fourths"
>     puts a.id, b.id, c.id
>     [ a, b, c ]
>   end
> 
>   def do_something2(a, b, c)
>     a << "-half"
>     b << "-thirds"
>     c << "-fourths"
>     puts a.id, b.id, c.id
>     [ a, b, c ]
>   end
> 
>   a = "one"
>   b = "two"
>   c = "three"
> 
>   puts "#{a}<#{a.id}>, #{b}<#{b.id}>, #{c}<#{c.id}>"
> 
>   x, y, z = do_something(a, b, c)
>   puts "#{x}<#{x.id}>, #{y}<#{y.id}>, #{z}<#{z.id}>"
>   puts "#{a}<#{a.id}>, #{b}<#{b.id}>, #{c}<#{c.id}>"
> 
>   x, y, z = do_something2(a, b, c)
>   puts "#{a}<#{a.id}>, #{b}<#{b.id}>, #{c}<#{c.id}>"
>   puts "#{x}<#{x.id}>, #{y}<#{y.id}>, #{z}<#{z.id}>"
> 
> This will help you understand. #<< modifies a String in-place. It's
> concatenation. += concatenates and creates a new string.
> 
> -austin