The iterator is used by keys, but not on each iteration of the for loop, but for the construction of the list of keys. Otherwise, the following program wouldn't output
$VAR1 = {
          'x' => 'cabd'
        };

[download]

The value would be shorter, as there would be less keys after the second iteration. 

#!/usr/bin/perl
use warnings;
use strict;

use Data::Dumper;

my %hash = ( a => 11,
             b => 12,
             c => 13,
             d => 14,
           );

for my $key (keys %hash) {
    delete $hash{$_} for qw( a b c d );
    $hash{'x'} .= $key;
}
print Dumper \%hash;

[download]
لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ

In reply to Re^3: Speeding up stalled script by choroba
in thread Speeding up stalled script by onlyIDleft

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