From: Robert Klemme <bob.news@...>
Date: 2005-05-07T16:44:28+09:00
Subject: Re: RCR 303: nil should accept missing methods and return nil


"Cyent" <cyent@xtra.co.nz> schrieb im Newsbeitrag 
news:pan.2005.05.07.00.06.00.185009@xtra.co.nz...
> On Fri, 06 May 2005 12:12:35 +0200, Robert Klemme wrote:
>
>>
>> I'm sorry, is this some kind of hoax?  A program will not magically be
>> correct simply because an error is hidden.  Think of all the subtle bugs
>> this would introduce, for example: you create an array with a fixed 
>> number
>> of elements and forget to give the default value 55.  Now math would 
>> work,
>> but the results would be wrong - and you might not even catch this.
>
> Think of an array with 42 elements. Access element 55. It returns nil. How
> is this different?

It's not different.  But it's not an argument in favor of your suggestion 
either.

> If you think through the default values for arithmetic operations on nil
> properly. My guess is the results in most case will be right.(How often do
> you initialize an array to 55? 99.9% of the time you expect it to be full
> of 0 or maybe 1.
>
> How about nil autoconverts to the identity element for all operations. ie.
> 0 for +, 1 for *, "" for string concat.

Not feasible since you would need a custom version of #coerce also and in 
that method you don't know the operator (+ or * for example) - at least not 
with standard means.  And I would not like to see these perlish dirty tricks 
in ruby.

> In which case more code simplification, more code that just works.

If you would drop this "code that just works" maybe I could find something 
useful in your suggestion.  I'm sorry, but I get the impression that you 
don't really seem to overlook the effects of your suggestion.

>> The article at
>> http://www.smalltalkchronicles.net/edition2-1/null_object_pattern.htm 
>> that
>> you refer to in the RCR states, that it's a bad idea to introduce this
>> change in Smalltalk because it would break too much code.  The situation 
>> in
>> Ruby is similar.
>
> Is it?
>
> I wwnt grepping through ruby 1.9 CVS (ok its a month or two old version)
> looking for some code that will break.
>
> I don't believe _anything_ will (currently) break.

But you should accept that others believe different.

    robert