Provided by: libutil-h2o-perl_0.18-2_all 
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.
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.
"-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".
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 like
"o2h" will no longer identify the objects as coming from "h2o".
"-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 named "main". With this option, the "Point" example in the
"Synopsis" can be written like the following, which can be useful if you want to add
more things to the "package", or perhaps if you want to write your methods as regular
"sub"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.
"-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 the "DESTROY" 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.
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", not "undef" itself!),
then passing a value of "undef" 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, plus "undef" 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.
This option was added in v0.18.
$hashref
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.
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, and
• the 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 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 - 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 $h2object"
This function takes an object as created by "h2o" and turns it back into a hashref by
making shallow copies of the object hash and any nested objects that may have been created
via "-recurse" (or created manually). This function is recursive by default because for a
non-recursive operation you can simply write: "{%$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).
Note that this function operates only on objects in the default package - it does not step
into plain arrayrefs or hashrefs, 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.
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 do 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) 2020-2022 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>.