use warnings;
use strict;

my @k = (1,2,3);

my $self = \@k; # an ARRAY reference

my $ret = foo($self, 'key');
print "$ret\n";

sub foo {
  my ($self, $key) = @_;

  (exists $self->{$key})
    ? return $self->{$key}
    : return 0;
}