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Re: [perl #118691] Perl crash on usage of index [-1] for array insubroutine call

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Karl Williamson
June 30, 2013 14:41
Re: [perl #118691] Perl crash on usage of index [-1] for array insubroutine call
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On 06/30/2013 08:03 AM, Father Chrysostomos via RT wrote:
> On Sun Jun 30 05:37:19 2013, jkeenan wrote:
>> On Sat Jun 29 10:13:54 2013, sprout wrote:
>>> On Sat Jun 29 08:06:12 2013, jkeenan wrote:
>>>> Your fourth call is not equivalent to your third call.  There's no
> '//'
>>>> operator imposing a context on $array[-1].  Perl looks at that
> variable
>>>> directly and notes that it runs afoul of the error condition described
>>>> above.  You're asking for $array[-1] to spring to life.  I'm sure that
>>>> there are others who can explain better than I can why we treat
> that as
>>>> a fatal error -- but fatal it is nonetheless.
>>> Whether this is a bug or no, it is certainly surprising--and fixable.
>> I think what is more surprising is that the poster's second and fourth
>> cases behave differently, i.e., that func($array[0]) has at least the
>> appearance of being well-behaved,
> That is a feature, added by 68dc07451.  One can pass nonexistent
> elements to functions without having them vivified immediately.  Only
> when $_[0] is modified inside the function is the element vivified.
>> whereas func($array[-1] generates a
>> fatal error.
>>> It’s just a matter of tweaking the defer logic in pp_aelem.  Then rvalue
>>> uses of $_[0] within the function will just work, but assignment to
>>> $_[0] will croak with the same error (i.e., the error will be delayed as
>>> long as possible).
>> Do we really want to do that?
> I say Yes! :-)


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