Here's a complete example of using the Perl vivification module, which you can find on CPAN. Perl's implicit instantiation of hash elements can readily be controlled with fine granularity:

#!/usr/bin/perl -w
use Data::Dumper;

my $hash =
{
    'id' => '992609516',
    'lat' => '37.7987145',
    'lon' => '-122.4436971',
    'tag' => {
             'operator' => { 'v' => 'CityCarShare' },
             'amenity'  => { 'v' => 'car_sharing' },
             },
};

print "Id:        $hash->{id}\n";
print "Amenity:   $hash->{tag}{amenity}{v}\n";
print "Bmenity:   $hash->{tag}{Bmenity}{v}\n";
print "Cmenity:   $hash->{tag}{Cmenity}{v}\n"
    if exists($hash->{tag}{Cmenity}{v});

no autovivification 'exists';
print "Dmenity:   $hash->{tag}{Dmenity}{v}\n"
    if exists($hash->{tag}{Dmenity}{v});

no autovivification;
print "Emenity:   $hash->{tag}{Emenity}{v}\n";
print Data::Dumper::Dumper(\$hash);
[download]

---

$VAR1 = \{
            'lat' => '37.7987145',
            'tag' => {
                       'amenity'  => {'v' => 'car_sharing' },
                       'operator' => {'v' => 'CityCarShare'},
                       'Bmenity'  => {},
                       'Cmenity'  => {},
                     },
            'lon' => '-122.4436971',
            'id' => '992609516'
          };
[download]