Re: exists $foo[7] and delete $foo[7]

[Nick Ing-Simmons <nick@ing-simmons.net>]

Tom Christiansen <tchrist@chthon.perl.com> writes:
>>> 
>>Nothing. There's nothing there, not even an undef() or an empty string.
>>That's why the array gets shorter if you delete its last value.
>
>You have to put *something* there!  There's a slot.  If there's not
>something there, then the slot is gone.  The picture abhors a vacuum.
>Is it undef?  Is it ""? Is it 0?  Is it false?  It it XXXXX?  
>Is it Jehosaphat? :-)

NULL vs undef vs '' is the bane of Tk so my immediate guess was that 
he had put NULL there rather than an SV *. 

This would have to be returned to perl code as undef but the C code
could tell them apart - hence distinguishing the 'exists' but undef
which occurs with hashes:

We can say:
  $hash{'foo'} = undef;
  if (exists $hash{'foo'}) { ... }

we could also do
  $array[12] = undef;
  if (exists $array[12]) { ... }

exists does not bother me.
delete does for two reasons:

 1. Why can I (apparently) delete $pseudo{'foo'}
    when I can't add $pseudo{'foo'} = 'xxx'.

 2. The initiated will think delete does splice.
    (I have users that try and use it that way already...)

-- 
Nick Ing-Simmons

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References to:

Tom Christiansen <tchrist@chthon.perl.com>

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