Clone

(source, CPAN)

version 0.50

NAME
SYNOPSIS
DESCRIPTION
EXAMPLES
LIMITATIONS
PERFORMANCE
CAVEATS
SEE ALSO
SUPPORT
COPYRIGHT
AUTHOR

#NAME

Clone - recursively copy Perl datatypes

#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 uses a recursion depth counter to prevent stack overflow. The default limit is 4000 rdepth units on Linux/macOS and 2000 on Windows/Cygwin. Each nesting level consumes approximately 2 rdepth units, so the effective limits are roughly 2000 nesting levels on Linux/macOS and 1000 on Windows/Cygwin.

For arrays, exceeding the limit triggers an iterative fallback that avoids stack overflow. For other reference types (hashes, scalars), exceeding the limit produces a warning and a shallow copy.

You can override the depth limit by passing it as the second argument to clone():
```
my $copy = clone($data, 8000);  # allow deeper recursion
```
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

Bug Reports and Feature Requests

Please report bugs on GitHub: https://github.com/garu/Clone/issues
Source Code

The source code is available on GitHub: https://github.com/garu/Clone

#COPYRIGHT

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.

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