[LRUG] To debug the impossible bug

[Murray Steele]

Hi Simon,

I don't suppose that the background of a question is a delegate method?
 E.g. the question is not nil, so the case fires that branch, but the object
that the question delegates background to *is* nil so you get the
NoMethodError.

Muz

On 3 August 2011 12:59, Tatsuya Ono <ononoma at gmail.com> wrote:

> 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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>>
>>
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