Re: Heisenberg Uncertainty Hash

[Roy Johnson]

Here's a demo of a sub you might find useful. It descends the hash chain checking existence at each level. It returns [a reference to, to ensure logical truth] the value if everything exists.

#!perl
use warnings;
use strict;

sub safe_exists {
    my ($href, @list_of_descent) = @_;
    use List::Util 'first';
    if (first {
            not (exists $href->{$_} and $href=$href->{$_})
        } @list_of_descent) {
        return ();
    }
    else {
        return \$href;
    }
}

my %hash = ('a' => {
                      'value' => 1,
                      'foo' => 'bar',
                   },
            'b' => {
                      'value' => 2,
                      'foo' => 'bar',
                   },
            'c' => {
                      'value' => 3,
                      'foo' => 'bar',
                   },
           );

for (qw(a b c d)) {
    if (my $href = safe_exists(\%hash, $_, 'value')) {
        print "$_ value is $$href\n";
    }
    else {
        print "Key $_ doesn't exist. Valid keys are: ";
        print join (", ", keys %hash), "\n";
    }
}