Data::Recursive - array and hash merge, deep clone, recursive data compare, done very fast, with C++ API.


This module performs merging, cloning and comparing data structures of any kind. It is written in C and performs as fast as possible.


    use Data::Recursive qw/clone lclone merge hash_merge array_merge compare/;
    $cloned = clone($data);
    $cloned = lclone($data);
    $result = merge($dest, $source, $flags);
    $result = hash_merge($dest, $source, $flags);
    $result = array_merge($dest, $source, $flags);
    $is_equal = compare($hash1, $hash2);
    $is_equal = compare($array1, $array2);
    $is_equal = compare($scalar1, $scalar2);


    #include <xs/clone.h>
    #include <xs/merge.h>
    #include <xs/compare.h>
    using namespace xs;
    Sv result = clone(data);
    Sv result = clone(data, 0);

    Sv    result = merge(dest, source, flags);
    Hash  result = hash_merge(dest, source, flags);
    Array result = array_merge(dest, source, flags);

    bool is_equal = compare(sv1, sv2);    


clone ($source, $flags = Data::Recursive::TRACK_REFS)

Makes a deep copy of $source and returns it.

Handles CODEREFs and IOREFs, but doesn't clone it, just copies pointer to the same CODE and IO into new reference. All other data types are cloned normally.

If clone encounters a blessed object and it has a HOOK_CLONE method, the return value of this method is used instead of a default behaviour. You can call clone($self) again from HOOK_CLONE if you need to, for example to prevent cloning some of your properties:

    sub HOOK_CLONE {
        my $self = shift;
        my $tmp = delete local $self->{big_obj_backref};
        my $ret = Data::Recursive::clone($self);
        $ret->{big_obj_backref} = $tmp;
        return $ret;

In this case second clone() call won't call HOOK_CLONE again and will clone $self in a standart manner.


Data::Recursive::TRACK_REFS is set (the default)

Handles cross-references: references to the same data will be the same references in cloned data. If a cycled reference is present in $source, it will remain cycled in cloned data.

Weak references are respected: weakref somewhere in $source becomes weakref to the cloned data in the result. However at least one strong reference to the same data must present somewhere in $source (and it will become of course a strong reference in the result). Otherwise (if no strong references pointing to such data present, only weak refs) all these weak refs will be undef in cloned result, because they can not exist without at least one strong reference. clone won't even try to clone those alone weak references (and will not call hook if those are objects with HOOK_CLONE defined).

In subsequent recursive calls from HOOK_CLONE this flag is always preserved, even if HOOK_CLONE calls clone($data, 0), i.e. keeping the behavior of the top call.

Data::Recursive::TRACK_REFS is unset

Does not detect cross-references: references to the same data will be different references. If a cycled reference is present in $source, it will throw an exception.

Does not respect weak references: if it discovers a weak reference somewhere in $source, it becomes a strong reference in cloned result. It behaves like this because in either case the resulting weak reference would be immediately destroyed after cloning as no one else has a strong reference to the resulting cloned data. If you want to handle weak references correctly, do not unset this flag.

Use this parameter (i.e. don't set TRACK_REFS flag) if you definitely know that your structure won't contain any cycled refs or weak refs to receive up to 30% performance profit. However if your data contains a lot of references which are references to the same data, unsetting this flag may significantly decrease performance (see PERFORMANCE why).

lclone ($source)

"Light clone", same as clone($data, 0)

hash_merge (\%dest, \%source, $flags = 0)

Merges hash $source into $dest. Merge is done very fast. $source and $dest must be HASHREFS or undefs. New keys from source are added to dest. Existing keys(values) are replaced. If a key contains HASHREF both in source and dest, they are merged recursively. Otherwise it gets replaced by value from source. Returns resulting hashref (it may or may not be the the same ref as $dest, depending on $flags provided).

$flags is a bitmask of the following flags listed. All constants are exported by default if you say

    use Data::Recursive;

By default, if a key contains ARRAYREF both in source and dest, it gets replaced by array from source. If you enable this flag, such arrays will be concatenated (like: push @{$dest->{key}}, @{$source->{key}).


If a key contains ARRAYREF both in source and dest, it gets merged. It means that $dest->{key}[0] is merged with $source->{key}[0], and so on. Values are merged using following rules: if both are hashrefs or arrayrefs, they are merged recursively, otherwise value in dest gets replaced.


If you set this flag, merge process won't override any existing and defined values in dest. Keep in mind that if you also set ARRAY_MERGE, then the same is in effect while merging array elements.

    my $hash1 = {a => 1, b => undef};
    my $hash2 = {a => 2, b => 3, c => undef };
    hash_merge($hash1, $hash2, LAZY);
    # $hash1 is {a => 1, b => 3, c => undef };

If enabled, values from source that are undefs won't replace anything in dest.

    my $hash1 = {a => 1};
    my $hash2 = {a => undef, b => undef, c => 2};
    hash_merge($hash1, $hash2, SKIP_UNDEF);
    # $hash1 is {a => 1, c => 2};

If enabled, values from source that are undefs acts as a 'deleters', i.e. the corresponding values get deleted from dest.

    my $hash1 = {a => 1, b => 2};
    my $hash2 = {a => undef};
    hash_merge($hash1, $hash2, DELETE_UNDEF);
    # $hash1 is {b => 2};

Makes deep copy of $dest, merges it with source and returns this new hashref.


By default, if any value from source replaces value from dest, it doesn't get deep copied. For example:

    my $hash1 = {};
    my $hash2 = {a => [1,2]};
    hash_merge($hash1, $hash2);
    shift @{$hash1->{a}};
    say scalar @{$hash2->{a}}; # prints 1

Moreover, even primitive values are not copied, instead they get aliased for speed. For example:

    my $hash1 = {};
    my $hash2 = {a => 'mystring'};
    hash_merge($hash1, $hash2);
    substr($hash1->{a}, 0, 2);
    say $hash2->{a}; # prints 'string'

If you enable this flag, replacing values from source will be copied (references - deep copied).



This is how undefined $source or undefined $dest are handled:

If $source is undef

Nothing is merged, however if COPY_DEST is set, deep copy of $dest is still returned. If $dest is also undef, then regardless of COPY_DEST flag, empty hashref is returned.

If $dest is undef

Empty hashref is created, merged with $source and returned.

merge ($dest, $source, $flags = 0)

Acts much like 'hash_merge', but receives any scalar as $dest and $source, not only hashrefs. Returns merged value which may or may not be the same scalar (modified or not) as $dest.

This function does the same work as 'hash_merge' does for its elements. I.e. if both $dest and $source are HASHREFs then they are merged via 'hash_merge'. If both are ARRAYREFs, then depending on $flags, $dest are either replaced, concatenated or merged. Otherwise $source replaces $dest following the rules described in 'hash_merge' function with respect to flags COPY_DEST, COPY_SOURCE and LAZY.

For example, if $source and $dest are scalars (not refs), and no flags provided, then $dest becomes equal $source. If LAZY is provided and $dest is not an undef, $dest is unchanged. If COPY_DEST is provided then $dest is unchaged and the result is returned in a new scalar. And so on.

However there is one difference: if $dest and $source are primitive scalars, instead of creating an alias, the $source variable is copied to $dest (or new result). If COPY_SOURCE is disabled, copying is not deep, like $dest = $source.

array_merge (\@dest, \@source, $flags = 0)

Recursively merges two arrays, using the same rules for each element as hash_merge with ARRAY_MERGE flag enabled.

It is the same as

    merge($dest, $source, $flags | ARRAY_MERGE);

but requires both $dest and $source to be an array references (or exception will be thrown).

compare ($data1, $data2)

Performs deep comparison and returns true if every element of $data1 is equal to corresponding element of $data2.

The rules of equality for two elements (including the top-level $data1 and $data2 itself):

If any of two elements is a reference.
If any of elements is a blessed object

If they are not objects of the same class, they're not equal

If class has overloaded '==' operation, it is used for checking equality. If not, objects' underlying data structures are compared.

If both elements are hash refs.

Equal if all of the key/value pairs are equal.

If both elements are array refs.

Equal if corresponding elements are equal (a[0] equal b[0], etc).

If both elements are code refs.

Equal if they are references to the same code.

If both elements are IOs (IO refs)

Equal if both IOs contain the same fileno.

If both elements are typeglobs

Equal if both are references to the same glob.

If both elements are refs to anything.

They are dereferenced and checked again from the beginning.

Otherwise (one is ref, another is not) they are not equal
If both elements are not references

Equal if perl's 'eq' or '==' (depending on data type) returns true.


    #include <xs/clone.h>
    #include <xs/merge.h>
    #include <xs/compare.h>
    using namespace xs;

All functions above behaves like its perl equivalents. See PERL FUNCTIONS docs.

For C++ SVAPI docs see XS::Framework

Sv clone (const Sv& data, int flags = CloneFlags::TRACK_REFS)

The only flag is xs::CloneFlags::TRACK_REFS which is set by default.

    auto hash = Hash::create(
        {"key1", Simple(1)},
        {"key2", Simple("val2")}
    hash["backref"] = Ref::create(hash);
    Hash copy = clone(hash);
    assert(copy != hash);
    Hash backref = copy["backref"];
    assert(copy == backref);

Hash merge (Hash dest, const Hash& source, int flags = 0)

Flags has the same names as perl flags. Located in xs::MergeFlags::******

Array merge (Array dest, const Array& source, int flags = 0)

Sv merge (Sv dest, const Sv& source, int flags = 0)

bool compare (const Sv& lh, const Sv& rh)


Please note, that although most of the time lclone is faster (about 10-30%) than clone because it doesn't need to track cross-references and handle weakrefs, on some certain data it can be much slower. For example

    my $hash = {a => 1, b => 2};
    my $data = [ ($hash) x 100 ];

In this case clone will be much faster, because it will clone $hash only once and keep the same reference in the cloned data.

Data::Recursive is about 4-10x faster than Clone or Storable::dclone

Clone::clone behaves like Data::Recursive::clone so these two were compared.

Storable::dclone behaves like Data::Recursive::lclone so these two were compared.


Pronin Oleg <>, Crazy Panda LTD


You may distribute this code under the same terms as Perl itself.