Suppose you have an object built around a complex hash. For some reason, you want to give other objects access to only part of it -- but you don't want to go through variable scoping or enforced encapsulation. Try this technique to make mini-objects.

Notes:

As for the tests, note that we display the keys for the top level object. Then, we display the keys for the newly created child object. Finally, we update a key nominally in the child object through the top object, and demonstrate that it is updated in the child object. No real thrill here, if you understand references, but a big caveat if you don't.

This one might be useful, somewhere.

#!/usr/bin/perl -w

use strict;

package SliceMe;

sub new {
    my $class = shift;
    $class = ref($class) || $class;
    my $self = {
        'top' => '1',
        'nest1' => {
            'hi' => '1',
            'there' => '2'
        },
        'nest2' => {
            'nest2a' => {
                'first' => '1',
                'second' => '2',
            },
        'nest2b' => 'not here'
        },
        'bottom' => '1',
    };

    bless ($self, $class);
    return $self;
}

sub slice {
    my $self = shift;
    my $class = ref($self) || $self;

    my $key = shift;
    my $hash;

    $hash = _pare($self, $key);
    bless ($hash, $class) if defined $hash;
    return $hash;
}

sub _pare {
    my $hash_ref = shift;
    my $key = shift;

    if (exists $hash_ref->{$key}) {
        return $hash_ref->{$key};
    } else {
        foreach my $try_hash (keys %$hash_ref) {
            _pare($try_hash, $key);
        }
        return undef;
    }
}

package main;

my $obj = new SliceMe;

print "obj keys:\n";
print "\t$_\n" foreach (keys %$obj);

my $obj_nest2 = $obj->slice("nest2");

print "obj_nest2 keys:\n";
print "\t$_\n" foreach (keys %$obj_nest2);

foreach (keys %$obj_nest2) {
    print "$_\t=>\t", $obj_nest2->{$_}, "\n";
}

$obj->{nest2}->{nest2b} = "okay, here now";

print $obj_nest2->{nest2b}, "\n";

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In reply to Cloning Pieces of an Object by chromatic

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