From: Gawnsoft <xlucid@...>
Date: 2003-08-05T12:38:12+09:00
Subject: Re: clearing a parameter in Ruby?

On Tue, 5 Aug 2003 07:23:34 +0900, Brian Candler <B.Candler@pobox.com>
wrote (more or less):

>On Tue, Aug 05, 2003 at 04:56:50AM +0900, Roy Patrick Tan wrote:
>> The problem is that in Ruby (and almost all modern imperative languages) 
>> two variables can refer to the same object. So part of the solution is 
>> never to use assignment except when creating an object (if you need a 
>> copy of an object, clone it). But that still leaves us w parameter 
>> passing, since a variable in the caller environment refers to an object 
>> that is also referred to by a variable in the called method... so I 
>> wanted to be able to clear the caller's variable.
>
>But there may well not be any variable to clear:
>
>    foo("hello")      # immediate object
>    foo(MAX_ENTRIES)  # constant
>    foo(x + 0)        # expression
>    foo(bar())        # expression
>    foo(Baz.new)      # expression
>
>What gets passed in to the method as an argument is an object reference,
>which may or may not have been stored in a local variable as an intermediate
>stage.
>
>"Never use assignment except when creating an object" also seems a strange
>rule, as I think it would rule out "a = a + 1", for example.

Welcome to the Smalltalk-ey world of a.add(1)     :-)

>If the actual issue is "object cannot be changed while it is in the
>container" then maybe you should look at Object#freeze. If you 'dup' it out
>of the container then the copy looses the frozen status.

Cheers, 
   Euan
Gawnsoft: http://www.gawnsoft.co.sr
Symbian/Epoc wiki:  http://html.dnsalias.net:1122
Smalltalk links (harvested from comp.lang.smalltalk)  http://html.dnsalias.net/gawnsoft/smalltalk