Util::H2O - Hash to Object: turns hashrefs into objects with accessors for keys


 use Util::H2O;
 my $hash = h2o { foo => "bar", x => "y" }, qw/ more keys /;
 print $hash->foo, "\n";           # accessor
 $hash->x("z");                    # change value
 $hash->more("cowbell");           # additional keys
 my $struct = { hello => { perl => "world!" } };
 h2o -recurse, $struct;            # objectify nested hashrefs as well
 print $struct->hello->perl, "\n";
 my $obj = h2o -meth, {            # code references become methods
     what => "beans",
     cool => sub {
         my $self = shift;
         print $self->what, "\n";
     } };
 $obj->cool;                       # prints "beans"
 h2o -classify=>'Point', {         # whip up a class
         angle => sub { my $self = shift; atan2($self->y, $self->x) }
     }, qw/ x y /;
 my $one = Point->new(x=>1, y=>2);
 my $two = Point->new(x=>3, y=>4);
 printf "%.3f\n", $two->angle;     # prints 0.927


This module allows you to turn hashrefs into objects, so that instead of $hash->{key} you can write $hash->key, plus you get protection from typos. In addition, options are provided that allow you to whip up really simple classes.

You can still use the hash like a normal hashref as well, as in $hash->{key}, keys %$hash, and so on, but note that by default this function also locks the hash's keyset to prevent typos there too.

This module exports a single function by default.

h2o @opts, $hashref, @additional_keys


If you specify an option with a value multiple times, only the last one will take effect.


Nested hashes are objectified as well. The only options that are passed down to nested hashes are -lock and -ro. None of the other options will be applied to the nested hashes, including @additional_keys. Nested arrayrefs are not recursed into.

Versions of this module before v0.12 did not pass down the -lock option, meaning that if you used -nolock, -recurse on those versions, the nested hashes would still be locked.


Any code references present in the hash at the time of this function call will be turned into methods. Because these methods are installed into the object's package, they can't be changed later by modifying the hash.

To avoid confusion when iterating over the hash, the hash entries that were turned into methods are removed from the hash. The key is also removed from the "allowed keys" (see the -lock option), unless you specify it in @additional_keys. In that case, you can change the value of that key completely independently of the method with the same name.

-class => classname

Specify the class name into which to bless the object (as opposed to the default: a generated, unique package name in Util::H2O::).

Note: If you use this option, -clean defaults to false, meaning that the package will stay in Perl's symbol table and use memory accordingly, and since this function installs the accessors in the package every time it is called, if you re-use the same package name, you will get "redefined" warnings. Therefore, if you want to create multiple objects in the same package, you should probably use -new.

-classify => classname

Short form of the options -new, -meth, -class => classname.


Generates a constructor named new in the package. The constructor works as a class and instance method, and dies if it is given any arguments that it doesn't know about. If you want more advanced features, like required arguments, validation, or other initialization, you should probably switch to something like Moo instead.

-clean => bool

Whether or not to clean up the generated package when the object is destroyed. Defaults to false when -class is specified, true otherwise. If this is false, be aware that the packages will stay in Perl's symbol table and use memory accordingly.

-lock => bool

Whether or not to use Hash::Util's lock_ref_keys to prevent modifications to the hash's keyset. Defaults to true. The -nolock option is provided as a short form of -lock=>0.

Keysets of objects created by the constructor generated by the -new option are also locked. Versions of this module before v0.12 did not lock the keysets of new objects.

Note that on really old Perls, that is, before Perl v5.8.9, Hash::Util and its lock_ref_keys are not available, so the hash is never locked on those versions of Perl. Versions of this module before v0.06 did not lock the keyset. Versions of this module as of v0.12 issue a warning on old Perls.


Short form of the option -lock=>0.


Makes the entire hash read-only using Hash::Util's lock_hashref and the generated accessors will also throw an error if you try to change values. In other words, this makes the object and the underlying hash immutable.

You cannot specify any @additional_keys with this option enabled unless you also use the -new option - the additional keys will then only be useful as arguments to the constructor. This option can't be used with -nolock or -lock=>0.

This option was added in v0.12. Using this option will not work and cause a warning when used on really old Perls (before v5.8.9), because this functionality was not yet available there.


You must supply a plain (unblessed) hash reference here. Be aware that this function does modify the original hashref(s) by blessing it and locking its keyset (the latter can be disabled with the -lock option), and if you use -meth or -classify, keys whose values are code references will be removed.

An accessor will be set up for each key in the hash; note that the keys must of course be valid Perl identifiers for you to be able to call the method normally.

When -clean is true (the default, unless you use -class), the hash may not contain a key named DESTROY. When -new is used, the hash may not contain a key named new. If the hash contains a key named AUTOLOAD, see "AUTOLOAD".


Methods will be set up for these keys even if they do not exist in the hash.


The (now blessed and optionally locked) $hashref.



If your hash contains a key named AUTOLOAD, or this key is present in @additional_keys, this module will set up a method called AUTOLOAD, which is subject to Perl's normal autoloading behavior - see "Autoloading" in perlsub and "AUTOLOAD" in perlobj. Without the -meth option, you will get a "catch-all" accessor to which all method calls to unknown method names will go, and with -meth enabled (which is implied by -classify), you can install your own custom AUTOLOAD handler by passing a coderef as the value for this key. However, it is important to note that enabling autoloading removes any typo protection on method names.

See Also

Inspired in part by lock_keys from Hash::Util.

Many, many other modules exist to simplify object creation in Perl. This one is mine ;-P

Similar modules include Object::Adhoc, Object::Anon, Hash::AsObject, Object::Result, and Hash::Wrap, the latter of which also contains a comprehensive list of similar modules.

For real OO work, I like Moo and Type::Tiny.

Author, Copyright, and License

Copyright (c) 2020-2021 Hauke Daempfling (

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

For more information see the Perl Artistic License, which should have been distributed with your copy of Perl. Try the command perldoc perlartistic or see