From: "Eric I." <rubytraining@...>
Date: 2008-11-26T12:25:22+09:00
Subject: Re: How to use a passing argument(returned argument)?

On Nov 25, 8:49 pm, ±è ÁØ¿µ <jy...@altibase.com> wrote:
> Hello, everyone !!!
>
> I have question about how to use a passing argument. firstly let me  
> show sample code.
>
> a = 0
>
> def set10(aArg)
>         aArg = 10
> end
>
> set10(a)
>
> p a <--- I wanna get 10 as a result.
>
> How can I do for this one?

Well, Ruby, being a purely object-oriented language, means that
assigning a value to a variable assigns it to a new object (instance)
without affecting the original.  So in your example, you just make the
parameter aArg refer to a new number leaving the original untouched.

To alter the data in a parameter, you would have to call a method on
the parameter that changes the data.  For example:

----

def method1(string)
  string.upcase!
end

s = "hello"
method1(s)
p s  # displays "HELLO"

----

Now, some classes have immutable instances -- instances that cannot
have the data within them altered.  Fixnum, Bignum, and Float (the
basic numeric types) are all immutable.  So that presents a problem.

What you could do is wrap the immutable instance in a mutable class,
as in:

----

require 'delegate'

class Mutable < SimpleDelegator
  def initialize(value)
    @value = value
    super(@value)
  end

  def reassign(new_value)
    @value = new_value
    __setobj__(@value)
  end
end

def method2(number)
  number.reassign(10)
end

n = Mutable.new(3)
method2(n)
p n  # displays 10

n = Mutable.new("test")
p n  # displays "test"
method2(n)
p n  # displays 10

----

I hope that's helpful.

Eric

====

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