From: Mohammad Khan <mkhan@...>
Date: 2005-01-20T01:10:22+09:00
Subject: Re: value by reference

#!/usr/bin/env ruby

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

# scenario 1
puts "before do_something : #{a.inspect}, #{b.inspect}, #{c.inspect}"
do_something( a, b, c)
puts "after do_something  : #{a.inspect}, #{b.inspect}, #{c.inspect}"	# a, b, c not changed
#do_something( a.clone, b.clone, c.clone)
#puts "after clone         : #{a.inspect}, #{b.inspect}, #{c.inspect}"	# can't clone Fixnum

# scenario 2
puts "before              : #{f.inspect}"
another_do_something(f)
puts "after with f        : #{f.inspect}"				# f changed
another_do_something(f.clone)
puts "after with f.clone  : #{f.inspect}"				# f not changed, it make sense


What is the difference between scenario 1 and scenario 2?
What is making scenario 1 not changed?

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.

MOhammad