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Object-HashBase-0.016
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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

HOOKS

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:

READ ONLY

use Object::HashBase qw/-foo/;

DEPRECATED SETTER

use Object::HashBase qw/^foo/;

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.

ISA AND ROLE PREFIXES

Two import prefixes provide shortcuts for declaring parent classes and consuming roles.

PARENT PREFIX: @

use Object::HashBase qw/@Some::Parent::Class foo bar/;

This loads Some::Parent::Class and pushes it onto @ISA. Equivalent to:

use parent 'Some::Parent::Class';
use Object::HashBase qw/foo bar/;

Multiple parents can be declared:

use Object::HashBase qw/@Parent::A @Parent::B foo/;

The prefix may be combined freely with attribute declarations in any order; parents are processed first regardless of position.

ROLE PREFIX: &

use Object::HashBase qw/&Some::Role::Name foo/;

This consumes a Role::Tiny role that itself uses Object::HashBase. The role's constants are copied into the consumer immediately so the $self->{+FOO} pattern resolves at compile time. The actual role composition via Role::Tiny->apply_roles_to_package is deferred until the end of the consumer's compile scope, so the consumer's own methods are present when role methods are composed (correct method-modifier and required-method semantics).

Requirements:

If a sub of the same name as a role constant already exists in the consumer package, the existing sub is kept and the role constant is not copied. No warning is issued.

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.

USING IN A ROLE

Object::HashBase can be used inside a Role::Tiny role:

package My::Role;
use Role::Tiny;
use Object::HashBase qw/foo -bar/;

sub greet { "hello " . $_[0]->{+FOO} }

When the package being imported into is a Role::Tiny role, Object::HashBase skips injection of new(), add_pre_init, add_post_init, _pre_init, and _post_init. Only accessor methods and constants are installed.

Important: use Role::Tiny; must appear before use Object::HashBase in the role package. Object::HashBase detects the role status of the target package at import time; if Role::Tiny has not yet been loaded, the target will be treated as a plain class and new() and the init hooks will be injected.

Consumers compose the role with the & prefix (recommended) or with a direct with() call. The & prefix copies the role's constants into the consumer at compile time, which is required for the $self->{+FOO} pattern in consumer methods to resolve.

GETTING A LIST OF ATTRIBUTES FOR A CLASS

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

SOURCE

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

MAINTAINERS

AUTHORS

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/