On Mon, 11 Jul 2011, Ben Coman wrote:

> 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 ?

I don't. :)

>
> Was your thought to create #objectSize in OrderedCollection or 
> OrderedCollectionInspector?  At first I assumed you meant

OrderedCollectionInspector.

> 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.

Kinda, but see what Nicolas wrote. Using his version (besides not 
evaluating "object size" twice for initialized objects) uses the stack 
optimally - no extra pushes, just use what's on the top. Also catching all 
Exceptions is unwelcome, you should only catch errors.

>
> 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 ].

I think the other solution is better, because it doesn't extend/modify 
OrderedCollection.


Levente

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