/ 
Clone-0.48
River stage five • 354 direct dependents • 13322 total dependents
⭐ Starred 7 GitHub stars
/ Clone

NAME

Clone - recursively copy Perl datatypes

Build Status CPAN version

SYNOPSIS

use Clone 'clone';

my $data = {
   set => [ 1 .. 50 ],
   foo => {
       answer => 42,
       object => SomeObject->new,
   },
};

my $cloned_data = clone($data);

$cloned_data->{foo}{answer} = 1;
print $cloned_data->{foo}{answer};  # '1'
print $data->{foo}{answer};         # '42'

You can also add it to your class:

package Foo;
use parent 'Clone';
sub new { bless {}, shift }

package main;

my $obj = Foo->new;
my $copy = $obj->clone;

DESCRIPTION

This module provides a clone() method which makes recursive copies of nested hash, array, scalar and reference types, including tied variables and objects.

clone() takes a scalar argument and duplicates it. To duplicate lists, arrays or hashes, pass them in by reference, e.g.

my $copy = clone (\@array);

# or

my %copy = %{ clone (\%hash) };

EXAMPLES

Cloning Blessed Objects

package Person;
sub new {
    my ($class, $name) = @_;
    bless { name => $name, friends => [] }, $class;
}

package main;
use Clone 'clone';

my $person = Person->new('Alice');
my $clone = clone($person);

# $clone is a separate object with the same data
push @{$person->{friends}}, 'Bob';
print scalar @{$clone->{friends}};  # 0

Handling Circular References

Clone properly handles circular references, preventing infinite loops:

my $a = { name => 'A' };
my $b = { name => 'B', ref => $a };
$a->{ref} = $b;  # circular reference

my $clone = clone($a);
# Circular structure is preserved in the clone

Cloning Weakened References

use Scalar::Util 'weaken';

my $obj = { data => 'important' };
my $container = { strong => $obj, weak => $obj };
weaken($container->{weak});

my $clone = clone($container);
# Both strong and weak references are preserved correctly

Cloning Tied Variables

use Tie::Hash;
tie my %hash, 'Tie::StdHash';
%hash = (a => 1, b => 2);

my $clone = clone(\%hash);
# The tied behavior is preserved in the clone

LIMITATIONS

  • Maximum Recursion Depth

    Clone supports structures up to 32,000 levels deep. Deeper structures will cause the clone operation to fail with an error. This limit prevents stack overflow and ensures safe operation.

  • Filehandles and IO Objects

    Filehandles and IO objects are cloned, but the underlying file descriptor is shared. Both the original and cloned filehandle will refer to the same file position. For DBI database handles and similar objects, Clone attempts to handle them safely, but behavior may vary depending on the object type.

  • Code References

    Code references (subroutines) are cloned by reference, not by value. The cloned coderef points to the same subroutine as the original.

  • Thread Safety

    Clone is not explicitly thread-safe. Use appropriate synchronization when cloning data structures across threads.

PERFORMANCE

Clone is implemented in C using Perl's XS interface, making it very fast for most use cases.

  • When to use Clone

    Clone is optimized for speed and works best with:

    • Shallow to medium-depth structures (3 levels or fewer)

    • Data structures that need fast cloning in hot code paths

    • Structures containing blessed objects and tied variables

  • When to use Storable::dclone

    Storable's dclone() may be faster for:

    • Very deep structures (4+ levels)

    • When you need serialization features

Benchmarking your specific use case is recommended for performance-critical applications.

CAVEATS

  • Cloned objects are deep copies

    Changes to the clone do not affect the original, and vice versa. This includes nested references and objects.

  • Object internals

    While Clone handles most blessed objects correctly, objects with XS components or complex internal state may not clone as expected. Test thoroughly with your specific object types.

  • Memory usage

    Cloning large data structures creates a complete copy in memory. Ensure you have sufficient memory available.

SEE ALSO

Storable's dclone() is a flexible solution for cloning variables, albeit slower for average-sized data structures. Simple and naive benchmarks show that Clone is faster for data structures with 3 or fewer levels, while dclone() can be faster for structures 4 or more levels deep.

Other modules that may be of interest:

Clone::PP - Pure Perl implementation of Clone

Scalar::Util - For weaken() and other scalar utilities

Data::Dumper - For debugging and inspecting data structures

SUPPORT

COPYRIGHT

Copyright 2001-2026 Ray Finch. All Rights Reserved.

This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

AUTHOR

Ray Finch <rdf@cpan.org>

Breno G. de Oliveira <garu@cpan.org>, Nicolas Rochelemagne <atoomic@cpan.org> and Florian Ragwitz <rafl@debian.org> perform routine maintenance releases since 2012.