/ 
Object-HashBase-0.015
River stage one • 1 direct dependent • 1 total dependent
/ Object::HashBase

NAME

Object::HashBase - Build hash based classes.

SYNOPSIS

A class:

package My::Class;
use strict;
use warnings;

# Generate 3 accessors
use Object::HashBase qw/foo -bar ^baz <bat >ban +boo/;

# Chance to initialize defaults
sub init {
    my $self = shift;    # No other args
    $self->{+FOO} ||= "foo";
    $self->{+BAR} ||= "bar";
    $self->{+BAZ} ||= "baz";
    $self->{+BAT} ||= "bat";
    $self->{+BAN} ||= "ban";
    $self->{+BOO} ||= "boo";
}

sub print {
    my $self = shift;
    print join ", " => map { $self->{$_} } FOO, BAR, BAZ, BAT, BAN, BOO;
}

Subclass it

package My::Subclass;
use strict;
use warnings;

# Note, you should subclass before loading HashBase.
use base 'My::Class';
use Object::HashBase qw/bub/;

sub init {
    my $self = shift;

    # We get the constants from the base class for free.
    $self->{+FOO} ||= 'SubFoo';
    $self->{+BUB} ||= 'bub';

    $self->SUPER::init();
}

use it:

package main;
use strict;
use warnings;
use My::Class;

# These are all functionally identical
my $one   = My::Class->new(foo => 'MyFoo', bar => 'MyBar');
my $two   = My::Class->new({foo => 'MyFoo', bar => 'MyBar'});
my $three = My::Class->new(['MyFoo', 'MyBar']);

# Readers!
my $foo = $one->foo;    # 'MyFoo'
my $bar = $one->bar;    # 'MyBar'
my $baz = $one->baz;    # Defaulted to: 'baz'
my $bat = $one->bat;    # Defaulted to: 'bat'
# '>ban' means setter only, no reader
# '+boo' means no setter or reader, just the BOO constant

# Setters!
$one->set_foo('A Foo');

#'-bar' means read-only, so the setter will throw an exception (but is defined).
$one->set_bar('A bar');

# '^baz' means deprecated setter, this will warn about the setter being
# deprecated.
$one->set_baz('A Baz');

# '<bat' means no setter defined at all
# '+boo' means no setter or reader, just the BOO constant

$one->{+FOO} = 'xxx';

Add pre_init and post-init:

Note: These are not provided if you define your own new() method (via a stub at the top).

Note: Single inheritence should work with child classes doing the pre/post init subs during construction, so long as all classes in the chain use a generated new(). This will probably explode badly in multiple-inheritence.

package My::Class;
use strict;
use warnings;

# Generate 3 accessors
use Object::HashBase qw/foo -bar ^baz <bat >ban +boo/;

# Do more stuff before init, add as many as you like by calling this
# multiple times with a different code block each time
add_pre_init {
    ...
};

# Chance to initialize defaults
sub init { ... }

# Do stuff after init, add as many as you want, they run in reverse order
add_post_init {
    my $self = shift;
    ...
};

sub print {
    my $self = shift;
    print join ", " => map { $self->{$_} } FOO, BAR, BAZ, BAT, BAN, BOO;
}

You can also call add_pre_init and add_post_init as class methods from anywhere to add init and post-init to the class.

Please note: This will apply to all future instances of the object created, but not past ones. This is a form of meta-programming and it is easy to abuse. It is also helpful for extending Object::HashBase.

My::Class->add_pre_init(sub { ... });
My::Class->add_post_init(sub { ... });

DESCRIPTION

This package is used to generate classes based on hashrefs. Using this class will give you a new() method, as well as generating accessors you request. Generated accessors will be getters, set_ACCESSOR setters will also be generated for you. You also get constants for each accessor (all caps) which return the key into the hash for that accessor. Single inheritance is also supported.

XS ACCESSORS

If Class::XSAccessor is installed, it will be used to generate XS getters and setters.

CAVEATS

The only caveat noticed so far is that if you take a reference to an objects attribute element: my $ref = \($obj->{foo}) then use $obj->set_foo(1), setting $$ref = 2 will not longer work, and getting the value via $val = $$ref will also not work. This is not a problem when Class::XSAccessor is not used.

In practice it will nbe VERY rare for this to be a problem, but it was noticed because it broke a performance optimization in Test2::API.

You can request an accessor NOT be xs with the '~' prefix:

use Object::HashBase '~foo';

The sample above generates foo() and set_foo() and they are NOT implemented in XS.

INCLUDING IN YOUR DIST

If you want to use HashBase, but do not want to depend on it, you can include it in your distribution.

$ hashbase_inc.pl Prefix::For::Module

This will create 2 files:

lib/Prefix/For/Module/HashBase.pm
t/HashBase.t

You can then use the includes Prefix::For::Module::HashBase instead of Object::HashBase.

You can re-run this script to regenerate the files, or upgrade them to newer versions.

If the script was not installed, it can be found in the scripts/ directory.

METHODS

PROVIDED BY HASH BASE

$it = $class->new(%PAIRS)
$it = $class->new(\%PAIRS)
$it = $class->new(\@ORDERED_VALUES)

Create a new instance.

HashBase will not export new() if there is already a new() method in your packages inheritance chain.

If you do not want this method you can define your own you just have to declare it before loading Object::HashBase.

package My::Package;

# predeclare new() so that HashBase does not give us one.
sub new;

use Object::HashBase qw/foo bar baz/;

# Now we define our own new method.
sub new { ... }

This makes it so that HashBase sees that you have your own new() method. Alternatively you can define the method before loading HashBase instead of just declaring it, but that scatters your use statements.

The most common way to create an object is to pass in key/value pairs where each key is an attribute and each value is what you want assigned to that attribute. No checking is done to verify the attributes or values are valid, you may do that in init() if desired.

If you would like, you can pass in a hashref instead of pairs. When you do so the hashref will be copied, and the copy will be returned blessed as an object. There is no way to ask HashBase to bless a specific hashref.

In some cases an object may only have 1 or 2 attributes, in which case a hashref may be too verbose for your liking. In these cases you can pass in an arrayref with only values. The values will be assigned to attributes in the order the attributes were listed. When there is inheritance involved the attributes from parent classes will come before subclasses.

HOOKS

$self->init()

This gives you the chance to set some default values to your fields. The only argument is $self with its indexes already set from the constructor.

Note: Object::HashBase checks for an init using $class->can('init') during construction. It DOES NOT call can() on the created object. Also note that the result of the check is cached, it is only ever checked once, the first time an instance of your class is created. This means that adding an init() method AFTER the first construction will result in it being ignored.

ACCESSORS

READ/WRITE

To generate accessors you list them when using the module:

use Object::HashBase qw/foo/;

This will generate the following subs in your namespace:

foo()

Getter, used to get the value of the foo field.

set_foo()

Setter, used to set the value of the foo field.

FOO()

Constant, returns the field foo's key into the class hashref. Subclasses will also get this function as a constant, not simply a method, that means it is copied into the subclass namespace.

The main reason for using these constants is to help avoid spelling mistakes and similar typos. It will not help you if you forget to prefix the '+' though.

READ ONLY

use Object::HashBase qw/-foo/;
set_foo()

Throws an exception telling you the attribute is read-only. This is exported to override any active setters for the attribute in a parent class.

DEPRECATED SETTER

use Object::HashBase qw/^foo/;
set_foo()

This will set the value, but it will also warn you that the method is deprecated.

NO SETTER

use Object::HashBase qw/<foo/;

Only gives you a reader, no set_foo method is defined at all.

NO READER

use Object::HashBase qw/>foo/;

Only gives you a write (set_foo), no foo method is defined at all.

CONSTANT ONLY

use Object::HashBase qw/+foo/;

This does not create any methods for you, it just adds the FOO constant.

NO XS

use Object::HashBase qw/~foo/;

This enforces that the getter and setter generated for foo will NOT use Class::XSAccessor even if it is installed.

SUBCLASSING

You can subclass an existing HashBase class.

use base 'Another::HashBase::Class';
use Object::HashBase qw/foo bar baz/;

The base class is added to @ISA for you, and all constants from base classes are added to subclasses automatically.

GETTING A LIST OF ATTRIBUTES FOR A CLASS

Object::HashBase provides a function for retrieving a list of attributes for an Object::HashBase class.

@list = Object::HashBase::attr_list($class)
@list = $class->Object::HashBase::attr_list()

Either form above will work. This will return a list of attributes defined on the object. This list is returned in the attribute definition order, parent class attributes are listed before subclass attributes. Duplicate attributes will be removed before the list is returned.

Note: This list is used in the $class->new(\@ARRAY) constructor to determine the attribute to which each value will be paired.

SOURCE

The source code repository for HashBase can be found at http://github.com/Test-More/HashBase/.

MAINTAINERS

Chad Granum <exodist@cpan.org>

AUTHORS

Chad Granum <exodist@cpan.org>

COPYRIGHT

Copyright 2017 Chad Granum <exodist@cpan.org>.

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

See http://dev.perl.org/licenses/