From: Ara.T.Howard@...
Date: 2005-05-07T00:34:25+09:00
Subject: Re: RCR 303: nil should accept missing methods and return nil

On Sat, 7 May 2005, Saynatkari wrote:

> Ara.T.Howard@noaa.gov wrote:
>> On Fri, 6 May 2005, Yukihiro Matsumoto wrote:
>>
>>> Hi,
>>>
>>> In message "Re: RCR 303: nil should accept missing methods and return
>>> nil"
>>>    on Fri, 6 May 2005 12:51:00 +0900, John Carter
>>> <john.carter@tait.co.nz> writes:
>>>
>>> |Be careful about exactly what is being asked for and what has been done
>>> |before. I once developed an OOP system were all objects would respond to
>>> |all undefined messages by doing nothing. I rapidly changed that to an
>>> |error condition as in that case the complaint that it hid bugs was
>>> valid.
>>>
>>> I know Objective-C's nil works like that.  I once developed an OOP
>>> system (which was an early version of Ruby) where nil would respond to
>>> all undefined messages by doing nothing.  In production code, it does
>>> nothing bad, since any production code should not raise an exception.
>>> Rather it introduces new scheme of error handling.
>>>
>>> But during development, it can hide bugs.  It is very difficult to
>>> distinguish correct error handling by ignoring unknown message, and
>>> uncontrolled unintentional misbehavior caused by bugs.  It's against
>>> the principle of "early death".
>>>
>>> Your proposal worth something, I think.  But it's not going to be seen
>>> in the near future of Ruby.
>>
>>
>> perhaps
>>
>>   nil.blackhole = true
>>
>> to change nil's behaviour.  that way it could be changed in production
>> code?
>
> Well, there is already $DEBUG. I think that should work fine, in case
> this proposal were accepted.

not at all - $DEBUG would need to be on by defualt then and most of the time
then and this causes reams of output on STDERR for many libs in addition to
subtly changing their behaviour.

what i'm suggesting is a 'normal' behaviour whereby nil throws NoMethodError
(current default) - note that this is NOT $DEBUG=true - and a built-in swith
to turn it off

   nil.blackhole = true

or perhaps a new global

   $NIL_BLACKHOLE = true

or maybe better

   NilClass::blackhole = true

to cause nil to obey the null pattern.

this feature wouldn't affect any code now since the normal behaviour would
remain the same.  $DEBUG is a global that affects tons of code in addition to
the (proposed) nil mods and therefore can't be used i think.

cheers.

-a
-- 
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