From: Robert Klemme <bob.news@...>
Date: 2005-01-15T20:26:11+09:00
Subject: Re: Duck Typing and automated Conversions


"itsme213" <itsme213@hotmail.com> schrieb im Newsbeitrag 
news:A5WFd.4845$Z%.29@fe1.texas.rr.com...
>
> "Robert Klemme" <bob.news@gmx.net> wrote
>> >> >     silly_example will not have other access to x, y
>> >> >     (*: since you did: str=str.to_str; count=count.to_int)
>> >>
>> >> Wrong, because to_str need not create a new instance:
>> >
>> > The fact that String#to_str returns self, and Fixnum.to_int returns
> self,
>> > is
>> > purely coincidental aliasing (from inside your method body). The
> original
>> > parm-list variables might as well be anonymous.
>>
>> But it's aliasing nevertheless and thus the caller can't rely on that the
>> instances he provides remain unchanged thinking that the body of the
> method
>> never gets access to them.  In fact, the aliasing might even be desired 
>> as
>> object creations are rather expensive and people are likely to provide
>> String instances where #to_str is needed.
>>
>> Of course you can view "original arguments" as anonymous but what
> difference
>> would that make?
>>
>> I don't seem to get your point with this.  Can you attempt another
>> explanation?
>
> Thank you. I may have stated too strongly, and you may have read more into
> it.

Yeah, that's likely.

> It's not a central part of your scheme (or my generalization). Here is
> my re-explanation:
>
> First, let's limit the scope: In any object graph just about any object 
> can
> be accessible from anywhere (via transitive returns from other methods,
> aliasing, globals, and constants like ObjectSpace). So in that extreme, 
> just
> about any method can be invoked on just about any object. We are not about
> address aliasing, so let's just focus on those objects that are passed 
> back
> and forth via method parameters.
>
> For these objects, your scheme allows us to say that the method body only
> has named references to things returned by methods on the object. Which
> means that it will not have references to the objects themselves (unless
> those methods on the objects themselves lead there, or it uses other paths
> through the object graph, such as via ObjectSpace).
>
> Any better?

Definitely!  But IMHO that weakened the property so much that I ask myself 
whether it's still useful. :-)

Cheers

    robert