From: Eleanor McHugh <eleanor@...>
Date: 2009-09-14T22:27:01+09:00
Subject: Re: Type checking function parameters

On 14 Sep 2009, at 08:43, Robert Klemme wrote:
>> I've rewritten the error handling so that it creates a message in  
>> the log
>> (assuming log_message to be defined somewhere in scope) and then re- 
>> raised
>> it so that the calling code can decide how to handle it. This  
>> allows an
>> error to be handled separately from a nil value return as the  
>> latter may
>> have some specific semantic meaning.
>
> I find it debatable whether this pattern does make sense: if the
> calling code can handle the exception in a meaningful way, there is no
> point in logging it, because that would attract suspicion where it is
> not in order.  I would say that logging is a form of handling, i.e. if
> the calling code does not know what to do about it, it can still log
> the error.  If you log it in the source location then this could be
> viewed as violating the principle of "let the calling code decide how
> to handle the exception".

Possibly, although there are cases where having subsystems log unusual  
occurrences for later analysis can be useful and it's also quite a  
nice pattern for triggering fail-safe behaviours at the right level of  
encapsulation when they are necessary. The caveat being that I very  
rarely find myself writing production code where that's necessary.

> One more reason against this pattern: if this is done on multiple
> levels you'll get the exact same error multiple times in the log which
> does not really help clear things up.

I wouldn't recommend using it at multiple levels unless each triggered  
different behaviour, or the triggered behaviour was clever enough to  
filter and distil. That may or may not be compatible with good data  
encapsulation depending on the problem domain.

>> I hope this all makes sense, but if not I'd be happy to discuss it  
>> further
>> off-list.
>
> Please let's keep it on list.  We would miss your mellow home brew  
> comments. :-)

Oh to see ourselves through the eyes of others...


Ellie

Eleanor McHugh
Games With Brains
http://slides.games-with-brains.net
----
raise ArgumentError unless @reality.responds_to? :reason