Name
Util::H2O - Hash to Object: turns hashrefs into objects with accessors for keys
Synopsis
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
Description
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
@opts
If you specify an option with a value multiple times, only the last one will take effect.
-recurse
-
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, but see the-arrays
option for that.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. -arrays
-
Like
-recurse
, but additionally,h2o
is applied to elements of nested arrays as well. The same options as with-recurse
are passed down to nested hashes and arrayrefs. Takes precedence over the-pass
option, i.e. if you use these two options together, arrayrefs are still descended into. Like hashrefs, the original arrays are modified!This option implies
-recurse
. This option was added in v0.20. -meth
-
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
or-classify
.If you wanted to generate a unique package name in a different package, you could use:
h2o -class => sprintf('My::Class::Name::_%x', $hash+0), $hash
, perhaps even in combination with-isa => 'My::Class::Name'
. However, keep in mind that you shouldn't step into another class' namespace without knowing that this won't cause conflicts, and also that not using the default class names means that functions likeo2h
will no longer identify the objects as coming fromh2o
. -classify => classname_string or $hashref
-
In the form
-classify => classname_string
, this is simply the short form of the options-new, -meth, -class => classname_string
.As of v0.16, in the special form
-classify => $hashref
, where the-classify
must be the last option in@opts
before the$hashref
, it is the same as-new, -meth, -class => __PACKAGE__, $hashref
- that is, the current package's name is used as the custom class name. It does not make sense to use this outside of an explicit package, since your class will be namedmain
. With this option, thePoint
example in the "Synopsis" can be written like the following, which can be useful if you want to add more things to thepackage
, or perhaps if you want to write your methods as regularsub
s:{ package Point; use Util::H2O; h2o -classify, { angle => sub { my $self = shift; atan2($self->y, $self->x) } }, qw/ x y /; }
Note
h2o
will remain in the package's namespace, one possibility is that you could load namespace::clean after you load this module.You might also note that in the above example, one could write
angle
as a regularsub
in the package. And at that point, one might recongize the similarity between the code and what one can do with e.g. Class::Tiny or even Moo. -isa => arrayref or scalar
-
Convenience option to set the
@ISA
variable in the package of the object, so that the object inherits from that/those package(s). This option was added in v0.14.Warning: The methods created by
h2o
will not call superclass methods. This means the parent class'DESTROY
method(s) are not called, and any accessors generated from hash keys are blindly overriden. -new
-
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. -destroy => coderef
-
Allows you to specify a custom destructor. This coderef will be called from the object's actual
DESTROY
in void context with the first argument being the same as the first argument to theDESTROY
method. Errors will be converted to warnings. This option was added in v0.14. -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, and any subs/methods in those packages may cause "redefined" warnings if the package name is re-used.As of v0.16, this module will refuse to delete the package if it is named
main
. -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. -nolock
-
Short form of the option
-lock=>0
. -ro
-
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.
-pass => "ref" or "undef"
-
When this option is set to
"undef"
(that's the string"undef"
, notundef
itself!), then passing a value ofundef
for the$hashref
will not result in a fatal error, the value will simply be passed through.When this option is set to the string
"ref"
, then any value other than a plain hashref that is a reference, including objects, plusundef
as above, will be passed through without modification. Any hashes nested inside of these references will not be descended into, even when-recurse
is specified. However,-arrays
takes precedence over this option, see its documentation.This option was added in v0.18.
$hashref
You must supply a plain (unblessed) hash reference here, unless you've specified the -pass
and/or -arrays
options. 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. If you use -arrays
, the elements of those arrays may also be modified.
An accessor will be set up for each key in the hash(es); note that the keys must of course be valid Perl identifiers for you to be able to call the method normally (see also the "Cookbook").
The following keys will be treated specially by this module. Please note that there are further keys that are treated specially by Perl and/or that other code may expect to be special, such as UNIVERSAL's isa
. See also perlsub and the references therein.
new
-
This key is not allowed in the hash if the
-new
option is on. DESTROY
-
This key is not allowed except if all of the following apply:
-destroy
is not used,-clean
is off (which happens by default when you use-class
),-meth
is on, andthe value of the key
DESTROY
is a coderef.
Versions of this module before v0.14 allowed a
DESTROY
key in more circumstances (whenever-clean
was off). AUTOLOAD
-
If your hash contains a key named
AUTOLOAD
, or this key is present in@additional_keys
, this module will set up a method calledAUTOLOAD
, 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 customAUTOLOAD
handler by passing a coderef as the value for this key - see "An Autoloading Example". However, it is important to note that enabling autoloading removes any typo protection on method names!
@additional_keys
Methods will be set up for these keys even if they do not exist in the hash.
Please see the list of keys that are treated specially above.
Returns
The (now blessed and optionally locked) $hashref
.
o2h @opts, $h2object
This function takes an object as created by h2o
and turns it back into a hashref by making shallow copies of the object hash and any nested objects that may have been created via -recurse
, -arrays
, or created manually. This function is recursive by default because for a non-recursive operation you can simply write: {%$h2object}
(making a shallow copy).
Unlike h2o
, this function returns a new hashref instead of modifying the given variable in place (unless what you give this function is not an h2o
object, in which case it will just be returned unchanged). Similarly, if you specify the -arrays
option, shallow copies of arrays will be returned in place of the original ones, with o2h
applied to the elements.
Note that this function operates only on objects in the default package - it does not step into plain hashrefs, it does not step into arrayrefs unless you specify -arrays
, nor does it operate on objects created with the -class
or -classify
options. Also be aware that because methods created via -meth
are removed from the object hash, these will disappear in the resulting hashref.
This function was added in v0.18.
@opts
If you specify an option with a value multiple times, only the last one will take effect.
-arrays
-
If you specify this option, nested arrayrefs are descended into as well.
This option was added in v0.20.
Cookbook
Keys with Spaces, Dashes, or Other Non-Identifier Characters
If the hash you want to pass to h2o
contains keys that are not usable as method names, such as keys containing spaces or dashes, you can transform the hash before passing it to h2o
. There are several ways to achieve this, including in plain Perl, but one of the easier ways is with pairmap
from the core module List::Util.
use List::Util 'pairmap';
my $hash = { "foo bar" => 123, "quz-ba%z" => 456 };
my $obj = h2o { pairmap { $a=~tr/a-zA-Z0-9/_/c; ($a,$b) } %$hash };
print $obj->foo_bar, $obj->quz_ba_z, "\n"; # prints "123456"
Using with Config::Tiny
One common use case for this module is to make accessing hashes nicer, like for example those you get from Config::Tiny. Here's how you can create a new h2o
object from a configuration file:
use Util::H2O 0.18 qw/ h2o o2h /; # v0.18 for o2h
use Config::Tiny 2.27; # v2.27 for writing file back out
my $config = h2o -recurse, {%{ Config::Tiny->read($config_filename) }};
say $config->foo->bar; # prints the value of "bar" in section "[foo]"
$config->foo->bar("Hello, World!"); # change value
# write file back out
Config::Tiny->new(o2h $config)->write($config_filename);
Debugging
Because the packages generated by h2o
are dynamic, note that any debugging dumps of these objects will be somewhat incomplete because they won't show the methods. However, if you'd like somewhat nicer looking dumps of the data contained in the objects, one way you can do that is with Data::Dump::Filtered:
use Util::H2O;
use Data::Dump qw/dd/;
use Data::Dump::Filtered qw/add_dump_filter/;
add_dump_filter( sub {
my ($ctx, $obj) = @_;
return { bless=>'', comment=>'Util::H2O::h2o()' }
if $ctx->class=~/^Util::H2O::/;
return undef; # normal Data::Dump processing for all other objects
});
my $x = h2o -recurse, { foo => "bar", quz => { abc => 123 } };
dd $x;
Outputs:
# Util::H2O::h2o()
{
foo => "bar",
quz => # Util::H2O::h2o()
{ abc => 123 },
}
An Autoloading Example
If you wanted to create a class where (almost!) every method call is automatically translated to a hash access of the corresponding key, here's how you could do that:
h2o -classify=>'HashLikeObj', -nolock, {
AUTOLOAD => sub {
my $self = shift;
our $AUTOLOAD;
( my $key = $AUTOLOAD ) =~ s/.*:://;
$self->{$key} = shift if @_;
return $self->{$key};
} };
Upgrading to Moo
Let's say you've used this module to whip up two simple classes:
h2o -classify => 'My::Class', {}, qw/ foo bar details /;
h2o -classify => 'My::Class::Details', {}, qw/ a b /;
But now you need more features and would like to upgrade to an actual OO system like Moo. Here's how you'd write the above code using that, with some Type::Tiny thrown in:
package My::Class2 {
use Moo;
use Types::Standard qw/ InstanceOf /;
use namespace::clean; # optional but recommended
has foo => (is=>'rw');
has bar => (is=>'rw');
has details => (is=>'rw', isa=>InstanceOf['My::Class2::Details']);
}
package My::Class2::Details {
use Moo;
use namespace::clean;
has a => (is=>'rw');
has b => (is=>'rw');
}
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. Also, see Class::Tiny for another minimalistic class generation module.
For real OO work, I like Moo and Type::Tiny (see "Upgrading to Moo").
Further modules that might be useful in combination with this one: Hash::Merge for merging hashes before using this module (for example, to supply default values for keys); Role::Tiny for applying roles.
See also Util::H2O::More by OODLER, a module with additional functionality on top of this module.
Special Thanks
Thanks to oodler577 on GitHub (OODLER on CPAN), whose many suggestions have inspired a lot of the features in this module!
Author, Copyright, and License
Copyright (c) 2020-2023 Hauke Daempfling (haukex@zero-g.net).
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 http://perldoc.perl.org/perlartistic.html.