Exist is the logical choice in his use case, and he asked for the rationale.

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 array	exists	defined	True
$a[0]	Yes	No	No	No
$a[1]	Yes	Yes	No	No
$a[2]	Yes	Yes	Yes	No
$a[3]	Yes	Yes	Yes	Yes
$a[4]	No	No	No	No

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".

To misquote Bill Clinton:

"It depends if your meaning of exist exists."

;)

Your table shows exactly a consistent behavior to exists when used with hashes. Unset values just don't exist.

$a[0] was never set, hence it doesn't exist.

I wasn't sure what you and sectokia meant with null-pointer, apparently it's the C-value of unset "gap" values¹ in the underlying C-array.

But those exist only on the C level, not logically in Perl.

> but there might be surprise cases (for (@a)? for ((), @a)? f(@a)?)

I don't understand, probably above my expertise.

Cheers Rolf
_{(addicted to the Perl Programming Language :)
see Wikisyntax for the Monastery}

¹) with an index smaller than the maximal index of a set value

It will help if undef isn't an acceptable value, which is a common scenario.

I should have qualified my answer, but I thought the OP said they were storing numbers. Those are the keys, though. woops.