[LRUG] To debug the impossible bug

[Tatsuya Ono]

Hi Simon,

It is a quite interesting problem. What I suspected were ...

1) Multithread issue
Daniel pointed out already and you seemed confident that it is not the
issue.

2) Error happened different place.
e.g.
class Question
  def background
    return @something.background # <= NoMethod error @something is nil here
  end
end

I know that unless you are bit careless, you wouldn't miss the backtrace.
However there might be a situation stack trace is not clear when the
background method is implemented with some kinds of meta programming trick.

I could not get any other idea apart from abobe for now. I would output log
to get more information.

e.g.

def page_description
  dump = @question.inspect
  begin
   case
     when @question then @question.background            # exception raised
here
     <snip other cases>
   end
  rescue NoMethodError=>e
    logger.info "Gotcha!!!!"
    logger.info "BEFORE: #{dump}
    logger.info "AFTER: #{@question.inspect}"
    logger.info "backtrace: #{e.backtrace}"
    logger.info "exception: #{e.message}"
    raise e
  end
end

Maybe we have to wait another one week, though, I am interested in what it
tells.


Tatsuya
twitter.com/ono

On 3 August 2011 12:28, Jordi Noguera Leon <jordinoguera83 at gmail.com> wrote:

> I'd rather use:
>
> def some_other_method
>   return foo.whatever if foo
>   return bar.whatever if bar
>   "some message"
> end
>
>
> On 3 August 2011 12:23, Viktor Tron <viktor.tron at gmail.com> wrote:
>
>> yes with no value, case becomes a concise way of writing if .. elsif ..
>> elsif conditionals
>> since simon's code is of this type, the bug he gets is a bug you expect
>> with the
>> case nil variant unless somewhere case is redefined to fall back to nil
>> with no args
>> Simon, is this not the 'case'? :)
>>
>> a little simplified irb for you:
>>
>> ruby-1.9.2-p180 :001 > case nil when nil then true else false end
>>  => true
>> ruby-1.9.2-p180 :002 > case when nil then true else false end
>>  => false
>>
>>
>>
>> On Wed, 03 Aug 2011 12:15:38 +0100, Tom Stuart <tom at therye.org> wrote:
>>
>>
>>> On 3 Aug 2011, at 12:12, Matthew Rudy Jacobs wrote:
>>>
>>>
>>>>
>>>> On 3 August 2011 12:09, Tom Stuart <tom at therye.org> wrote:
>>>>
>>>> See page 141 of the pickaxe for this use of case.
>>>>
>>>> Cheers,
>>>>
>>>> Tom
>>>>
>>>> Please enlighten me, then.
>>>> What's the usecase?
>>>>
>>>> Have never seen this done.
>>>>
>>>
>>> According to the Pickaxe '[this] form is fairly close to a series of if
>>> statements; it lets you list a series of conditions and execute a statement
>>> corresponding to the first one that's true."
>>>
>>> The code example there is:
>>>
>>> case
>>> when song.name == "Misty"
>>>  puts "Not again!"
>>> when song.duration > 120
>>>  puts "Too long!"
>>> when Time.now.hour > 21
>>>  puts "It's too late"
>>> else
>>>  song.play
>>> end
>>>
>>> It's pretty ugly, but it's valid Ruby and has nothing to do with the more
>>> usual use of case for comparison with === against multiple values.
>>>
>>> Cheers,
>>>
>>> Tom
>>>
>>>
>>
>> --
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