Levente Uzonyi wrote:
> On Mon, 11 Jul 2011, Ben Coman wrote:
>> I am writing some code that uses OrderedCollection and was tracing 
>> through it with the debugger when the debugger itself threw a DNU 
>> exception.  I narrowed down reproduction of this to executing the 
>> following line, clicking <Debug> then eight times <Into> :
>>>     self halt. OrderedCollection new: 5.
>> As far as I can determine, the root cause is that 
>> "OrderedCollectionInspector>>fieldList" calls "object size" which has 
>> the following implementation:
>>>     OrderedCollection>>size
>>>        ^ lastIndex - firstIndex + 1
>> where "lastIndex" is nil (and also "firstIndex" is nil).
> Back in the caller, rather than:
>>>     OrderedCollection>>fieldList
>>>         object ifNil: [ ^ OrderedCollection new].
>>>         ^ self baseFieldList ,
>>>             (object size <= (self i1 + self i2) <snip> 
>>
>>
>> this corrected the problem:
>>>     OrderedCollection>>fieldList
>>>         object ifNil: [ ^ OrderedCollection new].
>>>        [ object size ] on: Exception do: [ ^ self baseFieldList ].
>>>         ^ self baseFieldList ,
>>>             (object size <= (self i1 + self i2) <snip> 
> Yes, OrderedCollectionInspector should be changed, because that's what 
> causes the problem. I'd simply create an #objectSize method for it and 
> use that instead of object size.
> Levente
>> cheers, Ben 

Do you not like leaving the line "[ object size ] on: Exception do: [ ^ 
self baseFieldList ]" where it is ?

Was your thought to create #objectSize in OrderedCollection or 
OrderedCollectionInspector?  At first I assumed you meant 
OrderedCollection>>objectSize since OrderedCollectionInspector would 
still not know whether lastIndex was nil, and would seem to require the 
same exception handling.  But perhaps you meant that 
OrderCollectionInspector>>objectSize should just wrap the exception 
handling, and so would be...

OrderCollectionInspector>>objectSize
        [ object size ] on: Exception do: [ ^ 0 ].
       ^ object size.

OrderCollectionInspector>>fieldList
    object ifNil: [ ^ OrderedCollection new].
    ^ self baseFieldList ,
        (self objectSize <= (self i1 + self i2)
            ifTrue: [(1 to: self objectSize)
                        collect: [:i | i printString]]
            ifFalse: [(1 to: self i1) , (self objectSize - (self i2-1) 
to: self objectSize)
                        collect: [:i | i printString]])

Although I wonder if a cleaner implementation that exception handling 
could be...

OrderCollection>>hasSize
     lastIndex ifNil: [ ^false ].
     firstIndex ifNil: [ ^false ].
     ^true.

OrderCollectionInspector>>objectSize
        object hasSize ifTrue: [^ object size ] ifFalse: [ ^0 ].