Hello,

I would like to point out that both of these claims are unrealistic.

Specifically, Keith's examples all use low-level control-flow  
messages like "notNil ifTrue: [" whereas non-novice Smalltalkers  
should be using "ifNotNil:" and "ifNotNilDo: [:obj |".

The example would best be:

widget setStringValue: (#(office phone lastNumberDialed asString)  
inject: person into: [:obj :sel | obj ifNotNil: [obj perform: sel]])

without the message-eating Null pattern. Or if #perform: irks you,  
you can use:

widget setStringValue: (person office ifNotNilDo: [:office | office  
phone ifNotNilDo: [:phone | phone lastNumberDialed ifNotNilDo:  
[:number | number asString]]])

Like Keith, I find this a problem to have to write and maintain in  
code, but I'm not compelled to write long essays on it. I tend to  
think that chained message-sends represent a way in which distantly- 
related code can reach across protocols a bit too far. And Keith is  
being a bit unfair in that a several-page-long essay (with a really  
wide column justification width) will not be adequately rebutted in  
an email forum, thus keeping the discussion from balance.

My own view is that message-eating null is usable in controlled  
circumstances, but that in general one cannot control the  
circumstances (you can't know who *won't* receive a null as a  
parameter, so code written without that in mind fails in strange  
ways) in Smalltalk-80.

It is also worth pointing out that "message-eating null" most closely  
resembles the apposition of type T to NIL in Lisp, where one is the  
supertype of every type and the other is the subtype of every type.  
In Lisp, you do not interchange these, for good reason that I believe  
applies here but don't have time to gather evidence in support.

I think his packages which use message-eating-null would be a lot  
more palatable if they didn't...

On Jul 26, 2007, at 12:06 PM, Keith Hodges wrote:

>> Yuck, I wouldn't do either of those.  I would do:
>>
>> widget setStringValue: #(office phone lastNumberDialed asString)  
>> inject: person into: [:obj :sel| o == nil ifTrue: [ nil ] ifFalse:  
>> [ obj sel ] ]
> you would?
>
> To me the above looks as close to perl as smalltalk is hopefully  
> ever likely to get!
>
> ;-)

That is disingenuous. Please use honest arguments.

> Keith
>
> p.s. Someone once accused me of being a PL/1 programmer in a former  
> life.

--
-Brian
http://briantrice.com