I think some behavior in Perl hash usage has changed. It used to be that $hash{test_elem} would set that hash key to a value of '' (empty string).

But in the following program: 

#!/usr/local/bin/perl

use strict;
use warnings;

use Data::Dumper;


sub find_numbers {

  my ($amount, $map)=@_;

  my $start = 11;
  my @found;

  while ($amount--) {
    while ($map->{$start}) {
      ++$start;
    }
    push @found, $start++;
  }

  @found;

}

my %map = (
          '11' => 1,
          '12' => 1,
          '15' => 1,);

my @free_numbers = find_numbers(4, \%map);

die Dumper(\@free_numbers, \%map);

[download]
we see that %map does not end up having all the various values that were tested via the expression  while ($map->{$start})

Why is that?



The mantra of every experienced web application developer is the same: thou shalt separate business logic from display. Ironically, almost all template engines allow violation of this separation principle, which is the very impetus for HTML template engine development.

-- Terence Parr, "Enforcing Strict Model View Separation in Template Engines"

In reply to When testing for certain hash positions as non-zero, why werent the test positions set to empty string? by metaperl

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