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### Re: "A meditation on Hashes", or "Why i need more aspirin"

by nothingmuch (Priest)
 on Jun 20, 2006 at 10:00 UTC ( #556341=note: print w/replies, xml ) Need Help??

A lesser known fact is that you can delete array cells too.. The aspirin in this case is to think of arrays as arrays of pointers to scalars. If the pointer is nothing then the array cell doesn't exist. If the pointer leads to a scalar then you have a cell in which to store values. I think this is how arrays are implemented internally...
```#!/usr/bin/perl

use strict;
use warnings;
no warnings 'uninitialized';

my @array = 1 .. 5;

\$\ = "\n";

sub check {
print "array length: " . @array;

use tt;
[% FOR check IN ["exists", "defined", "true", "" ] %]
for my \$i ( 0 .. \$#array ) {
print "[% check %]([\$i]) is " . [% check %]( \$array[\$i] );
}
[% END %]
no tt;

print;
}

sub true { !!\$_[0] }

check;
delete \$array[\$_] for 2 .. 3; # creates a hole
check;
undef \$array[0]; # operates on the slot, not the array
check;
delete \$array[-1]; # reduces length
check;
undef @array; # clears the array
check;
@array = 1 .. 3;
check;
This yields:
```array length: 5
exists([0]) is 1
exists([1]) is 1
exists([2]) is 1
exists([3]) is 1
exists([4]) is 1
defined([0]) is 1
defined([1]) is 1
defined([2]) is 1
defined([3]) is 1
defined([4]) is 1
true([0]) is 1
true([1]) is 1
true([2]) is 1
true([3]) is 1
true([4]) is 1
([0]) is 1
([1]) is 2
([2]) is 3
([3]) is 4
([4]) is 5

array length: 5
exists([0]) is 1
exists([1]) is 1
exists([2]) is
exists([3]) is
exists([4]) is 1
defined([0]) is 1
defined([1]) is 1
defined([2]) is
defined([3]) is
defined([4]) is 1
true([0]) is 1
true([1]) is 1
true([2]) is
true([3]) is
true([4]) is 1
([0]) is 1
([1]) is 2
([2]) is
([3]) is
([4]) is 5

array length: 5
exists([0]) is 1
exists([1]) is 1
exists([2]) is 1
exists([3]) is 1
exists([4]) is 1
defined([0]) is
defined([1]) is 1
defined([2]) is
defined([3]) is
defined([4]) is 1
true([0]) is
true([1]) is 1
true([2]) is
true([3]) is
true([4]) is 1
([0]) is
([1]) is 2
([2]) is
([3]) is
([4]) is 5

array length: 4
exists([0]) is 1
exists([1]) is 1
exists([2]) is 1
exists([3]) is 1
defined([0]) is
defined([1]) is 1
defined([2]) is
defined([3]) is
true([0]) is
true([1]) is 1
true([2]) is
true([3]) is
([0]) is
([1]) is 2
([2]) is
([3]) is

array length: 0

array length: 3
exists([0]) is 1
exists([1]) is 1
exists([2]) is 1
defined([0]) is 1
defined([1]) is 1
defined([2]) is 1
true([0]) is 1
true([1]) is 1
true([2]) is 1
([0]) is 1
([1]) is 2
([2]) is 3
-nuffin
zz zZ Z Z #!perl

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