Perl serialize nested reference to string

Question

I'm looking for a solution for using complex keys (arbitrary references) as hash keys, except that they perform deep comparison on the keys as opposed to reference comparison.

I am looking for a function preferably in a core module that serializes arbitrary references (possibly excluding subroutine and typeglob references) to strings in such a way that they can be reconstituted later.

 my @complex_key = qw[key1 key2];
 my %hash;
 $hash{serialize([@complex_key])} = 'value';

  deserialize((keys %hash)[0]);
   # should deeply equal [@complex_key]

Schwern · Accepted Answer · 2015-12-19 20:37:33Z

5

There's no need to serialize all that data just to have a (potentially enormous) hash key. Instead, take the checksum of the data structure and use that for a key. Store the original key as part of the value.

Here's an example using perl5i to do the deep checksum.

use perl5i::2;
$hash{@stuff->mo->checksum} = {
    key   => \@stuff,
    value => 'value'
};

my $value = $hash{@stuff->mo->checksum}{value};
my $key   = $hash{@stuff->mo->checksum}{key};

You can wrap this in a little class to make it more convenient.

sub get {
    my $self = shift;
    my $key  = shift;

    return $self->{$key->mo->checksum}{value};
}

sub set {
    my $self = shift;
    my($key, $val) = @_;

    $self->{$key->mo->checksum} = $val;

    return;
}

sub each {
    my $self = shift;
    my $code = shift;

    my $val;
    while( (undef, $val) = each %$self ) {
        $code->($val->{key}, $val->{value});
    }

    return;
}

$obj->set(\@stuff, "value");
my $value = $obj->get(\@stuff);

$obj->each( func($key, $val) {
    say "$key -> $val\n";
}

answered Dec 19, 2015 at 20:37

Schwern

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2 Comments

Greg Nisbet Over a year ago

The Perl5i module is really cool, but I'm not sure I need an entire meta object extension to construct a deep checksum of an arbitrary value. I checked the implementation of checksum and it uses Data::Dumper to get a string representation of arbitrary values and to sort keys in hashes. What is the advantage of that approach over setting $Storable::canonical = 1, and then hashing the resulting serialization of the data structure?

Schwern Over a year ago

@GregoryNisbet perl5i brings all sorts of other value to your fingertips, and $foo->mo->checksum is already implemented and tested. But any serialization + checksum technique will work. The point is the technique, not the implementation.

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