and he asked for the rational.

Hasn't that been answered already?

It's because exists $a[i] doesn't really check if the element exists in the array. It's not sufficient for the element to be part of the array; the pointer in the array buffer must be something other than NULL.

For example, 

my @a;
$a[1] = undef;
$a[2] = 0;
$a[3] = 7;

[download]
Element of the arrayexistsdefinedTrue
$a[0]YesNoNoNo
$a[1]YesYesNoNo
$a[2]YesYesYesNo
$a[3]YesYesYesYes
$a[4]NoNoNoNo

It might also be warning of problems with using NULL as a special value. I suspect Perl is quite consistent at keeping NULL elements NULL, but there might be surprise cases (for (@a)? for ((), @a)? f(@a)?)

Update: Replaced some uses of "exists".

In reply to Re^3: Using exists to check element in array by ikegami
in thread Using exists to check element in array by david

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