Clone::Fast(3) Natively copying Perl data structures


use strict;
use warnings;
use Clone::Fast qw( clone );
use Data::Dumper;
# Though that may be the easiest thing to do, there
# are also other options:
# use Clone::Fast; # While using Clone::Fast::clone
# {
# no strict 'refs';
# *clone = \&Clone::Fast::clone;
# }
# eval( "sub clone { Clone::Fast::clone }" );
my $original = bless( { 'a' => [ qw( a b c d ) ] }, 'main' );
my $copy = clone( $original );
# Notice the original and copy are no longer the same,
# although they look exactly the same
print "Different memory segments\n" if ( $original ne $copy );
print "Same structure\n" if ( Dumper( $original ) eq Dumper( $copy ) );


Essentially, this module is a very optimized version of Clone::More. By taking advantage of one of Clone::More's 'OPTIMIZATION_HACKS' as well as removing all the Pure Perl from the "", I was able to gain a lot of speed out of the module. Essentially, though, the core of the module is exactly as that of Clone::More.

You will see that by useing Benchmark::cmpthese, I ran a simple comparison between Storable::dclone, Clone::More::clone, and Clone::Fast::clone. You will (should) begin to see the reason why I loaded this module along side of Clone::More.

                                   Rate    Storable Clone::More Clone::Fast
        Storable     7552/s          --        -39%        -59%
        Clone::More 12400/s         64%          --        -33%
        Clone::Fast 18442/s        144%         49%          --

For more information relative to the DESCRIPTION of this module, I recommend peeking into the POD written for Clone::More (I took more time with it ;) )


As noted in Clone::More, this module started as a patch for Clone with repsect to a large memory leak a team I was working closely with at the time fell across once implemented the cloning into a Perl application. The unfortunate part is that I wasn't able to patch the Clone module without a complete re-factor (I still have no idea where the leak is in Clone), and have not been able to get ahold of Ray Finch, the current author and supporter of Clone. Every thing considered, I loaded up this and it's counter part Clone::More - both a little different from one another, and both a little different from Clone still.



Clone is the primary function from within the provided module. By passing a scalar reference to this routine, you will expect to get a returned scalar reference that will no longer have any reference to the originating reference. However, references deeper into the structure will still uphold the references within the structure.

Example being:

        use Clone::Fast qw( clone );
        my $foo = { 'a' => 'b' };
        my $bar = { 'a' => $foo, 'b' => $foo };
        my $baz = clone( $bar );
        print "\$foo and \$bar are different references\n" if ( $foo ne $bar );
        print "\$foo->{'a'} and \$bar->{'a'} are different references\n" if ( $foo->{'a'} ne $bar->{'a'} );
        print "\$foo->{'a'} and \$foo->{'b'} are the same, however\n" if ( $foo->{'a'} eq $bar->{'b'} );

This makes sense, although this can be modified as well. By using the internal variable, BREAK_REFS, you are also allowed to break internal references (may break up circular references, although won't fix the circular reference in the originating reference).


Much like the Perl Storable module (available in all current Perl distributions), "Clone::Fast" allows for hooks that will be accessed when cloning any object that has a hook defined. This can be very handy where Inside Out objects would not normally be cloned. WHHAAATT???? What I mean is, only the reference of an object will be cloned, not the internal stash of the object. Therefore, accessors that are defined within an inside out object will not be cloned. There is no real safe way to do this, with the exception of cloning the entire class stash, breaking more things than it will fix. Again, the reference of the object will be fully cloned, and the object it's self will be a new reference, although it will be an empty object. Subsiquently, such as most inside out objects, the blessed reference is of a scalar type; an integer indicating the object id. When cloning this, you would end up with two objects of the same type with the same object id. The hooks have been added in an attempt to prevent this from happening.


Again, much like Storable (though a little better, I hope), the function will be called *AFTER* the clone operation has completed on the object being cloned. The routine will have two scalar references passed via the stack, representing both the cloned object as well as the source of the clone. This *should* allow for the programatic manipulation of the object before it gets returned to the caller, or placed into the refering structure.

As an example, I will use the following object to define a 'hooked' object:

        package Hookable;
        use strict;
        use warnings;
        use Clone::Fast qw( clone );
        sub new { bless {}, shift }
        sub CLONEFAST_clone {
                # Where clone is the cloned object from the source, where source
                # was the originating reference
                my ( $clone, $source ) = @_;
                # I am going to pretend the source has a list of defined methods,
                # of which I want to clone and transfer to the clone; outside
                # of the blessed hash-refrence that is the source of the object
                $clone->$_( clone( $source->$_() ) ) for ( qw( get_method_1 get_method_2 get_method_3 ) );
                # At this point, the cloned object will also have a set of cloned
                # fields from the source.  If, by chance, any of the values of the
                # defined attribtes are other 'Hookable' objects, the same routine
                # will be called on that object as well.
                # The API requires me to return the new $clone, this will be returned to
                # the caller
                return $clone;

Using the package from above, I will now use an example of a script where I will demonstrate how the whole thing comes together:

        #!/usr/bin/perl -w
        use strict;
        use Clone::Fast qw( clone );
        my $hookable  = Hookable->new();
        $hookable->{'hash_stuff'} = 'some value';
        my $structure = {
                'hookable' => $hookable,
                'new'      => Hookable->new(),
                'deeply'   => {
                        'hookable' => $hookable,
                        'new'      => Hookable->new();
        my $cloned = clone( $sturcture );

This script will demonstrate a number of things. 1.) "Clone::Fast::clone" will, automagically call the hook on all instances of the Hookable. Though the hash_stuff key will automatically be cloned before the hook is ever called. Subsiquently, the hashes in both values of hookable in the hash will be references of one another, though not references to the originating object. The Hookable->new() object, on the other hand, will not be referenced to anything of the similar like.

As a secondary note, it was originally thought to allow for hooks to show up before and after the cloning of the object. Though, that would allow for the full change of the cloning type; this would be very bad. Also, given that it is somewhat reasonable to believe hooks will only be used with inside out objects, we can also assume the cloning of a simple referent will be so lightweight that there will still be the benifit of having clone hook into the object. If anyone has beef with this paradigm, let me know and I'll change it.


The "ALLOW_HOOKS" variable will allow for the toggling behavior, telling "Clone::Fast" to check for hooks when cloning objects. (See "PRGRAMATIC HOOKS" for more details). The varialble will default to 'on', where "Clone::Fast" will always check each object for hooks defined within the object.

        use Clone::Fast qw( clone );
        $Clone::Fast::ALLOW_HOOKS = 1; # No need, this is default
        my $object = HasHooks->new();
        package HasHooks;
        use strict;
        use warnings;
        sub new { bless {}, shift }
        sub CLONEFAST_clone {
                my ( $clone, $source ) = @_;
                # Re-assigning the reference will now return the reference from the
                # C<Clone::Fast::clone> when cloning a HasHooks object, rather than
                # a cloned reference to the object.
                $clone = { 'object' => $clone };
                return $clone;
        use Clone::Fast qw( clone );
        $Clone::Fast::BREAK_REFS = 1;
        my $foo = { 'a' => 'b' };
        my $bar = { 'a' => $foo, 'b' => $foo };
        my $baz = clone( $bar );
        print "\$foo and \$bar are different references\n" if ( $foo ne $bar );
        print "\$foo->{'a'} and \$bar->{'a'} are different references\n" if ( $foo->{'a'} ne $bar->{'a'} );
        print "\$foo->{'a'} and \$foo->{'b'} are no longer the same\n" if ( $foo->{'a'} ne $bar->{'b'} );

You will see that by adding the BREAK_REFS flag, you will change the overall behavior of the routine. The BREAK_REFS flag must, simply, have truthfullness (as far as Perl is concerned) in order to be 'on'.


        $Clone::Fast::BREAK_REFS = 1;
        # Will do the same thing as:
        $Clone::Fast::BREAK_REFS = 'yes';
        # Will do the same thing as:
        $Clone::Fast::BREAK_REFS = ( 2 != 1 );

Albeit handy, this feature may also slow down the module by some degree. Therefore, there is some flexibility into whether or not you need to use this, and the functionality can be compiled out of the object; speeding up the cloning ability. Therefore, Re-compiling the mdule without MINDFUL_REFS will increase the speed of the module by a degree of 3x! If you KNOW you will never use the $Clone::Fast::BREAK_REFS and are confident with manually installing Perl modules from source, it is recommended you do so. There are comments in the XS source that will detail how to do this.

This configuration only applies to the "Clone::Fast::clone" routine.


Using Clone::Fast::clone
"Clone::Fast::clone" is an exported routine. You can either use it as such, or simply call it directly on the package.

Example w/ export:

        use Clone::Fast qw( clone );
        my $source = { 'a' => 'b' };
        my $clone  = clone( $source );

Example w/o export

        use Clone::Fast;
        my $source = { 'a' => 'b' };
        my $clone  = Clone::Fast::clone( $source );
Using Clone::Fast::(is_)?circular
The "Clone::Fast::(is_)?circular" routines will allow you to test whether or not a structure contains a ciruclar reference or not.


bless()'ed references (Perl objects)
This module works great for blessed references, how ever the paradigm changes when trying to clone inside out objects (or Conway's 'flywaight' style of object creation). Clone does not, nor will not, clone the stash of an object's class; this would break more than anything. Given this, HOOKS have been provided in order to programatically handle weird stuff like this. I am hoping applications, developers and all of the like whom are using inside out objects will know what the heck it is I'm talking about here. There is a lot more information about this in the PROGRAMATIC HOOKS section.
I really have no idea how this will work in a treadded environment. It should be OK, but there is no development that has taken this into account.
Hooks are pretty new, and may have some problems within them. Please, if you find anything you don't expect; feel free to bug it and I will try to patch it up ASAP.


Trevor Hall, <[email protected]>


Copyright (C) 2006 by Trevor Hall

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