From: Huw Collingbourne <huw@...>
Date: 2006-02-24T19:28:34+09:00
Subject: Re: Everything's an object, right?

To the best of my knowledge everything (apart from integers) is passed by 
reference. However, 99% of the time this doesn't matter. In 'pure OOP' 
programming, 'messages' are sent to 'methods' and they respond with new 
data. If you only ever use return values you won't see inconsistent 
behaviour and you won't break encapsulation (which, in effect, using ByRef 
arguments to obtain new values does).

To clarify. There are a few string methods which alter the original string 
object. This is also the case if you index into a string to change a char.

However, when you evaluate an expression, this yields a new object so that 
in the following:

x = x + 1

The expression on the right yields a value which is assigned to a new 
object, x, on the left. In other words, the x on the right is a different 
object from the x on the left. Since methods which alter data usually do so 
in the process of evaluation and assignment, most of the time any object 
(such as x) which "goes in" is assigned to a new object (with the same name) 
by the time the method ends. This explains why many people believe that 
arguments are sent 'by value' - because, in most cases, the value of any 
argument that goes into a method is not changed. Rather, a new object is 
created during the process of evaluation and assignment.

If this is confusing, just stick to the 'pure OOP' way of doing things and 
always use return values; never try to use the values of ingoing arguments 
as 'ByRef' parameters. Life is much simpler that way ;-)

best wishes
Huw Collingbourne
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