Hi All,

The reason why #veryDeepCopy works, and #copy doesn't (besides some 
missing #postCopy methods) is that some nodes in the matcher graph are 
referenced from more than one place, so #copy will create two copies of 
these, while #veryDeepCopy will only create one.
Still, #veryDeepCopy does make unnecessary object duplications, so we 
should find a way to work this around.
One example for a double reference is in RxMatcher >> #makeOptional:, 
where the dummy link is added to the branch and the end of the matcher 
chain as well.

Levente

On Thu, 19 May 2016, Rein, Patrick wrote:

> 
> Hi Nicolas,
> 
> 
> thanks for looking into this, as this is kind of tricky to get right on my own without any discussions. What I did is to look into the value of
> anRmxLink in #makeQuantified:min:max: before and after a copy. What happens is that the backward references in RxmBranch nodes back to other
> RxmLink nodes break as the references get only copied separately and result in two different objects. As a result the copied structure does not
> include any back references. The postCopy callbacks do not solve that issue but do, to my understanding at that point, only implement the
> recursion of the copying. veryDeepCopy however produces the same node structure which is what is actually needed for the quantified structures.
> This way the termiateWith: method works correctly and the generating of broken matcher structures is fixed. However, it changes the behavior
> slightly (as in the Regex-Tests-Core commit in the inbox) so I am not yet sure whether this is only a technical fix or also a correct fix of the
> behavior.
> 
> 
> Does that sound somewhat reasonable? :)
> 
> 
> Bests
> 
> Patrick
> 
> 
> 
> __________________________________________________________________________________________________________________________________________________
> From: squeak-dev-bounces at lists.squeakfoundation.org <squeak-dev-bounces at lists.squeakfoundation.org> on behalf of Nicolas Cellier
> <nicolas.cellier.aka.nice at gmail.com>
> Sent: Thursday, May 19, 2016 22:18
> To: The general-purpose Squeak developers list
> Subject: Re: [squeak-dev] The Trunk: Regex-Core-pre.51.mcz  
> Hi Patrick,
> IMO copy should copy deep enough without the need to invoke veryDeepCopy.
> Wouldn't it be a missing postCopy in RxmLookahead?
> 
> postCopy
>     super postCopy.
>     lookahead := lookahead copy
> 
> 2016-05-19 20:49 GMT+02:00 <commits at source.squeak.org>:
>       Patrick Rein uploaded a new version of Regex-Core to project The Trunk:
>       http://source.squeak.org/trunk/Regex-Core-pre.51.mcz
>
>       ==================== Summary ====================
>
>       Name: Regex-Core-pre.51
>       Author: pre
>       Time: 19 May 2016, 8:49:05.994548 pm
>       UUID: 49e3e29a-cf96-4f42-a8f1-4af75dbb9bca
>       Ancestors: Regex-Core-ul.50
>
>       Fixes an erroring test of RxMatcher by replacing a copy with a veryDeepCopy to sustain the integrity of the RxmLink tree.
>
>       =============== Diff against Regex-Core-ul.50 ===============
>
>       Item was changed:
>         ----- Method: RxMatcher>>makeQuantified:min:max: (in category 'private') -----
>         makeQuantified: anRxmLink min: min max: max
>               "Perform recursive poor-man's transformation of the {<min>,<max>} quantifiers."
>               | aMatcher |
>
>               "<atom>{,<max>}       ==>  (<atom>{1,<max>})?"
>               min = 0 ifTrue: [
>                       ^ self makeOptional: (self makeQuantified: anRxmLink min: 1 max: max) ].
>
>               "<atom>{<min>,}       ==>  <atom>{<min>-1, <min>-1}<atom>+"
>               max ifNil: [
>       +               ^ (self makeQuantified: anRxmLink min: 1 max: min-1) pointTailTo: (self makePlus: anRxmLink veryDeepCopy) ].
>       -               ^ (self makeQuantified: anRxmLink min: 1 max: min-1) pointTailTo: (self makePlus: anRxmLink copy) ].
>
>               "<atom>{<max>,<max>}  ==>  <atom><atom> ... <atom>"
>               min = max
>                       ifTrue: [
>       +                       aMatcher := anRxmLink veryDeepCopy.
>       +                       (min-1) timesRepeat: [ aMatcher pointTailTo: anRxmLink veryDeepCopy ].
>       -                       aMatcher := anRxmLink copy.
>       -                       (min-1) timesRepeat: [ aMatcher pointTailTo: anRxmLink copy ].
>                               ^ aMatcher ].
>
>               "<atom>{<min>,<max>}  ==>  <atom>{<min>,<min>}(<atom>{1,<max>-1})?"
>       +       aMatcher := self makeOptional: anRxmLink veryDeepCopy.
>       -       aMatcher := self makeOptional: anRxmLink copy.
>               (max - min - 1) timesRepeat: [
>       +                aMatcher := self makeOptional: (anRxmLink veryDeepCopy pointTailTo: aMatcher) ].
>       -                aMatcher := self makeOptional: (anRxmLink copy pointTailTo: aMatcher) ].
>               ^ (self makeQuantified: anRxmLink min: min max: min) pointTailTo: aMatcher!
> 
> 
> 
> 
>