++ed by:
Author image Peter Shangov
and 1 contributors


Data::AsObject - Easy OO access to complex perl data structures


version 0.07


    use Data::AsObject qw(dao);

    my $book = dao {
        name      => "Programming Perl",
        authors   => ["Larry Wall", "Tom Christiansen", "Jon Orwant"],


    print $book->name                # prints "Programming Perl"
    print $book->authors(0)          # prints "Larry Wall"
    my $array_ref = $book->authors   # $array_ref is ["Larry Wall", "Tom Christiansen", "Jon Orwant"]
    my @array = $book->authors->list # @array is ("Larry Wall", "Tom Christiansen", "Jon Orwant")
    $book->{publisher} = "O'Reilly";
    print $book->publisher           # prints "O'Reilly"


Data::AsObject provides easy object-oriented access to complex and arbitrarily nested perl data structures. It is particularly suitable for working with hash-based representation of XML data, as generated by modules like XML::Complie or XML::TreePP.


Version 0.06 of Data::AsObject broke backward compatibility with two changes that may break existing scripts.

  • Automatic dereferencing in list context is no longer provided. Use the list method instead.

  • An attempt to access an non-existing hash key by default now dies rather than simply produce a warning. Either explicitly request Data::AsObject not to die on missing hash keys, or use an exception handling mechanism to check if the data you want to access is actually there.


These are some of the reasons why you may want to use Data::AsObject:

Object-oriented syntax

The object-oriented syntax may sometimes be more appropriate than the traditional hashref and arrayref syntax.

Protection from misspelled hash key names

Since Data::AsObject does not preform any autovivification, it protects you from misspelling a hash key when accessing its value (but see also Hash::Util for more robust ways to do that).

Easy access to hash keys with non-standard symbols

If your hashes contain a lot of keys with dashes or colons, as is often the case with keys representing xml element names, Data::AsObject can automatically access such keys by substituting underscores for the non-standard symbols.

Easy dereferencing of arrayrefs

If you have a lot of arrayrefs in your data structure that often need to be traversed, e.g. with grep, map or foreach, Data::AsObject provides a list method on arrayrefs to automatically dereference them.



Takes as input one or more hash or array references, and returns one or more objects (Data::AsObject::Hash or Data::AsObject::Array respectively) that can be used to access the data structures via an object oriented interface.

Data::AsObject uses Sub::Exporter and allows you to import the dao sub in one of three modes:

strict mode
    use Data::AsObject dao => { mode => 'strict' };

In this mode (which is the default) dao will produce an object that dies whenever you try to invoke a hash key that does not exist.

loose mode
    use Data::AsObject dao => { mode => 'loose' };

In this mode dao will produce an object that returns undef and issues a warning whenever you try to invoke a hash key that does not exist.

strict mode
    use Data::AsObject dao => { mode => 'silent' };

In this mode dao will produce an object that returns undef whenever you try to invoke a hash key that does not exist, but does not complain.


Working with hashes

To access hash elements by key, use the hash key as method name:

    my $data = dao { three => { two => { one => "kaboom" } } };
    print $data->three->two->one; # kaboom

If a hash key contains one or more colons or dashes, you can access its value by substituting underscores for the colons or dashes (the underlying hash key name is not modified).

    my $data = dao {
        'xml:lang'     => "EN",
        'element-name' => "some name",

    print $data->xml_lang     # "EN"
    print $data->element_name # "some name"

Working with arrays

To access array items pass the item index as an argument to the hash that contains the array:

    my $data = dao {
        uk => ["one", "two", "three", "four"],
        spain => [
            { name => 'spanish', numbers => ["uno", "dos", "tres", "cuatro"] },
            { name => 'catalan', numbers => ["un", "dos", "tres", "quatre"] },

    print $data->en(1) # two
    print $data->spain(0)->numbers(3); # cuatro

Array of array structures are a little bit clumsier to work with. You will need to use the get method of Data::AsObject::Array and pass it the index of the item you want to access:

    my $data = dao [
        ["one", "two", "three", "four"]
        ["uno", "dos", "tres", "cuatro"],
        ["un", "dos", "tres", "quatre"],

    print $data->get(2)->get(0); # un

Arrayrefs have a dereferencing list method. For example:

    my $data = dao {
        spain => [
            { name => 'spanish', numbers => ["uno", "dos", "tres", "cuatro"] },
            { name => 'catalan', numbers => ["un", "dos", "tres", "quatre"] },

    foreach my $n ( $data->spain->list ) {
        print $n->name . " ";
    } # spanish catalan

Modifying data

Data::AsObject only provides accessor functions. To modify data, access the respective hash or array element directly:

    my $data = dao {};
    $data->{one} = "uno";
    print $data->one # uno


No autovivification is performed by default (but see FUNCTIONS above). An attempt to access a hash or array element that does not exist will produce a fatal error. Use an exception handling mechanism such as Try::Tiny.

    use Try::Tiny;

    my $data = dao {
        uk      => ["one", "two", "three", "four"],
        spain   => ["uno", "dos", "tres", "cuatro"],
        germany => ["eins", "zwei", "drei", "vier"].

    try {
        my $numbers = $data->bulgaria;
    } catch {
        warn "No info about Bulgaria!";

See also can below.

Data::AsObject::Hash and special methods

If $data isa Data::AsObject::Hash:


$data->can will return the value of the $data->{can} element. $data->can("some_hash_key") will properly return undef if some_hash_key does not exists, or a reference to a sub that returns $data->{some_hash_key} otherwise.

    my $data = dao {
        uk      => ["one", "two", "three", "four"],
        # ...

    warn "No info about Bulgaria!" unless $data->can('bulgaria');

Calling $data->VERSION will attempt to return the value of a hash element with a key "VERSION". Use Data::AsObject->VERSION instead.

others special methods

All other special methods and functions (isa, ref, DESTROY) should behave as expected.


Please report any bugs or feature requests to bug-data-object at rt.cpan.org, or through the web interface at http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Data-Object. I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.



Peter Shangov <pshangov@yahoo.com>


This software is copyright (c) 2011 by Peter Shangov.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.