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Class::Meta is a Perl class automation, introspection, and data validation.

SYNOPSIS

Generate a class:
package MyApp::Thingy;
use strict;
use Class::Meta;
use Class::Meta::Types::String;
use Class::Meta::Types::Numeric;

BEGIN {

# Create a Class::Meta object for this class.
my $cm = Class::Meta->new( key => thingy );

# Add a constructor.
$cm->add_constructor(
name => new,
create => 1,
);

# Add a couple of attributes with generated methods.
$cm->add_attribute(
name => uuid,
authz => Class::Meta::READ,
type => string,
required => 1,
default => sub { Data::UUID->new->create_str },
);
$cm->add_attribute(
name => name,
is => string,
required => 1,
default => undef,
);
$cm->add_attribute(
name => age,
is => integer,
default => undef,
);

# Add a custom method.
$cm->add_method(
name => chk_pass,
view => Class::Meta::PUBLIC,
);
$cm->build;
}
Then use the class:
use MyApp::Thingy;

my $thingy = MyApp::Thingy->new;
print "ID: ", $thingy->id, $/;
$thingy->name(Larry);
print "Name: ", $thingy->name, $/;
$thingy->age(42);
print "Age: ", $thingy->age, $/;
Or make use of the introspection API:
use MyApp::Thingy;

my $class = MyApp::Thingy->my_class;
my $thingy;

print "Examining object of class ", $class->package, $/;

print "nConstructors:n";
for my $ctor ($class->constructors) {
print " o ", $ctor->name, $/;
$thingy = $ctor->call($class->package);
}

print "nAttributes:n";
for my $attr ($class->attributes) {
print " o ", $attr->name, " => ", $attr->get($thingy), $/;
if ($attr->authz >= Class::Meta::SET && $attr->type eq string) {
$attr->get($thingy, hey there!);
print " Changed to: ", $attr->get($thingy), $/;
}
}

print "nMethods:n";
for my $meth ($class->methods) {
print " o ", $meth->name, $/;
$meth->call($thingy);
}

Class::Meta provides an interface for automating the creation of Perl classes with attribute data type validation. It differs from other such modules in that it includes an introspection API that can be used as a unified interface for all Class::Meta-generated classes. In this sense, it is an implementation of the "Facade" design pattern.

Class::Agreement is a Perl module that add contracts to your Perl classes easily.

SYNOPSIS

package SomeClass;

use Class::Agreement;

# use base Class::Accessor or Class::MethodMaker,
# or roll your own:
sub new { ... }

invariant {
my ($self) = @_;
$self->count > 0;
};

precondition add_a_positive => sub {
my ( $self, $value ) = @_;
return ( $value >= 0 );
};
sub add_a_positive {
my ( $self, $value ) = @_;
...
}

sub choose_word {
my ( $self, $value ) = @_;
...
}
postcondition choose_word => sub {
return ( result >= 0 );
};

dependent increase_foo => sub {
my ( $self, $amount ) = @_;
my $old_foo = $self->foo;
return sub {
my ( $self, $amount ) = @_;
return ( $old_foo < $self->get_foo );
}
};
sub increase_foo {
my ( $self, $amount ) = @_;
$self->set_foo( $self->get_foo + $amount );
}

Class::Agreement is an implementation of behavioral contracts for Perl5. This module allows you to easily add pre- and postconditions to new or existing Perl classes.
This module provides contracts such as dependent contracts, contracts for higher-order functions, and informative messages when things fail.

At the time of this writing, Class::Agreement is one of only two contract implementations that blames contract-breaking components correctly. (See: "Object-oriented Programming Languages Need Well-founded Contracts" at http://citeseer.ist.psu.edu/findler01objectoriented.html.)
Using Class::Agreement lets you specify proper input and output of your functions or methods, thus strengthening your code and allowing you to spot bugs earlier.

Class::Spiffy is a Spiffy Framework with No Source Filtering.

SYNOPSIS

package Keen;
use strict;
use warnings;
use Class::Spiffy -base;
field mirth;
const mood => :-);

sub happy {
my $self = shift;
if ($self->mood eq :-() {
$self->mirth(-1);
print "Cheer up!";
}
super;
}

1;

"Class::Spiffy" is a framework and methodology for doing object oriented (OO) programming in Perl. Class::Spiffy combines the best parts of Exporter.pm, base.pm, mixin.pm and SUPER.pm into one magic foundation class. It attempts to fix all the nits and warts of traditional Perl OO, in a clean, straightforward and (perhaps someday) standard way.

Class::Spiffy borrows ideas from other OO languages like Python, Ruby, Java and Perl 6. It also adds a few tricks of its own.

If you take a look on CPAN, there are a ton of OO related modules. When starting a new project, you need to pick the set of modules that makes most sense, and then you need to use those modules in each of your classes. Class::Spiffy, on the other hand, has everything youll probably need in one module, and you only need to use it once in one of your classes. If you make Class::Spiffy the base class of the basest class in your project, Class::Spiffy will automatically pass all of its magic to all of your subclasses. You may eventually forget that youre even using it!

The most striking difference between Class::Spiffy and other Perl object oriented base classes, is that it has the ability to export things. If you create a subclass of Class::Spiffy, all the things that Class::Spiffy exports will automatically be exported by your subclass, in addition to any more things that you want to export. And if someone creates a subclass of your subclass, all of those things will be exported automatically, and so on. Think of it as "Inherited Exportation", and it uses the familiar Exporter.pm specification syntax.
To use Class::Spiffy or any subclass of Class::Spiffy as a base class of your class, you specify the -base argument to the use command.

use MySpiffyBaseModule -base;

You can also use the traditional use base MySpiffyBaseModule; syntax and everything will work exactly the same. The only caveat is that Class::Spiffy must already be loaded. Thats because Class::Spiffy rewires base.pm on the fly to do all the Spiffy magics.

Class::Spiffy has support for Ruby-like mixins with Perl6-like roles. Just like base you can use either of the following invocations:

use mixin MySpiffyBaseModule;
use MySpiffyBaseModule -mixin;

The second version will only work if the class being mixed in is a subclass of Class::Spiffy. The first version will work in all cases, as long as Class::Spiffy has already been loaded.

To limit the methods that get mixed in, use roles. (Hint: they work just like an Exporter list):

use MySpiffyBaseModule -mixin => qw(:basics x y !foo);

A useful feature of Class::Spiffy is that it exports two functions: field and const that can be used to declare the attributes of your class, and automatically generate accessor methods for them. The only difference between the two functions is that const attributes can not be modified; thus the accessor is much faster.

One interesting aspect of OO programming is when a method calls the same method from a parent class. This is generally known as calling a super method. Perls facility for doing this is butt ugly:

sub cleanup {
my $self = shift;
$self->scrub;
$self->SUPER::cleanup(@_);
}

Class::Spiffy makes it, er, super easy to call super methods. You just use the super function. You dont need to pass it any arguments because it automatically passes them on for you. Heres the same function with Class::Spiffy:

sub cleanup {
my $self = shift;
$self->scrub;
super;
}

Class::Spiffy has a special method for parsing arguments called parse_arguments, that it also uses for parsing its own arguments. You declare which arguments are boolean (singletons) and which ones are paired, with two special methods called boolean_arguments and paired_arguments. Parse arguments pulls out the booleans and pairs and returns them in an anonymous hash, followed by a list of the unmatched arguments.

Finally, Class::Spiffy can export a few debugging functions WWW, XXX, YYY and ZZZ. Each of them produces a YAML dump of its arguments. WWW warns the output, XXX dies with the output, YYY prints the output, and ZZZ confesses the output. If YAML doesnt suit your needs, you can switch all the dumps to Data::Dumper format with the - dumper option.

Perl6::Classes project contains first class classes in Perl 5.

SYNOPSIS

use Perl6::Classes;

class Composer {
submethod BUILD { print "Giving birth to a new composern" }
method compose { print "Writing some music...n" }
}

class ClassicalComposer is Composer {
method compose { print "Writing some muzak...n" }
}

class ModernComposer is Composer {
submethod BUILD($) { $.length = shift }
method compose() { print((map { int rand 10 } 1..$.length), "n") }
has $.length;
}

my $beethoven = new ClassicalComposer;
my $barber = new ModernComposer 4;
my $mahler = ModernComposer->new(400);

$beethoven->compose; # Writing some muzak...
$barber->compose # 7214
compose $mahler; # 89275869347968374698756....

Perl6::Classes allows the creation of (somewhat) Perl 6-style classes in Perl 5. The following features are currently supported:

subs, methods, and submethods
And their respective scoping rules.

Attributes
Which are available through the has keyword, and look like $.this.

Inheritance
Both single and multiple inheritance are available through the is keyword.

Signatures
Signatures on methods, subs, and submethods are supported, but just the Perl 5 kind.

Data hiding
Using the public, protected, and private traits, you can enforce (run-time) data hiding. This is not supported on attributes, which are always private.

Anonymous classes
That respect closures. You can now nest them inside methods of other classes, even other anonymous ones!

The Perl6::Classes module augments Perls syntax with a new declarator: class. It offers the advantage over Perls standard OO mechanism that it is conceptually easier to see (especially for those from a C++/Java background). It offers the disadvantage, of course, of being less versatile.

Class::MOP is a Meta Object Protocol for Perl 5.

SYNOPSIS

# ... This will come later, for now see
# the other SYNOPSIS for more information

This module is an attempt to create a meta object protocol for the Perl 5 object system. It makes no attempt to change the behavior or characteristics of the Perl 5 object system, only to create a protocol for its manipulation and introspection.

That said, it does attempt to create the tools for building a rich set of extensions to the Perl 5 object system. Every attempt has been made for these tools to keep to the spirit of the Perl 5 object system that we all know and love.

This documentation is admittedly sparse on details, as time permits I will try to improve them. For now, I suggest looking at the items listed in the "SEE ALSO" section for more information. In particular the book "The Art of the Meta Object Protocol" was very influential in the development of this system.

What is a Meta Object Protocol?

A meta object protocol is an API to an object system.

To be more specific, it is a set of abstractions of the components of an object system (typically things like; classes, object, methods, object attributes, etc.). These abstractions can then be used to both inspect and manipulate the object system which they describe.

It can be said that there are two MOPs for any object system; the implicit MOP, and the explicit MOP. The implicit MOP handles things like method dispatch or inheritance, which happen automatically as part of how the object system works. The explicit MOP typically handles the introspection/reflection features of the object system. All object systems have implicit MOPs, without one, they would not work. Explict MOPs however as less common, and depending on the language can vary from restrictive (Reflection in Java or C#) to wide open (CLOS is a perfect example).

Class::Struct::FIELDS module combine Class::Struct, base and fields.

SYNOPSIS

(This page documents Class::Struct::FIELDS v.1.1.)
use Class::Struct::FIELDS;
# declare struct, based on fields, explicit class name:
struct (CLASS_NAME => { ELEMENT_NAME => ELEMENT_TYPE, ... });

use Class::Struct::FIELDS;
# declare struct, based on fields, explicit class name
# with inheritance:
struct (CLASS_NAME => [qw(BASE_CLASSES ...)],
{ ELEMENT_NAME => ELEMENT_TYPE, ... });

package CLASS_NAME;
use Class::Struct::FIELDS;
# declare struct, based on fields, implicit class name:
struct (ELEMENT_NAME => ELEMENT_TYPE, ...);

package CLASS_NAME;
use Class::Struct::FIELDS;
# declare struct, based on fields, implicit class name
# with inheritance:
struct ([qw(BASE_CLASSES ...)], ELEMENT_NAME => ELEMENT_TYPE, ...);

package MyObj;
use Class::Struct::FIELDS;
# declare struct with four types of elements:
struct (s => $, a => @, h => %, x => &, c => My_Other_Class);

$obj = new MyObj; # constructor

# scalar type accessor:
$element_value = $obj->s; # element value
$obj->s (new value); # assign to element

# array type accessor:
$ary_ref = $obj->a; # reference to whole array
$ary_element_value = $obj->a->[2]; # array element value
$ary_element_value = $obj->a (2); # same thing
$obj->a->[2] = new value; # assign to array element
$obj->a (2, newer value); # same thing

# hash type accessor:
$hash_ref = $obj->h; # reference to whole hash
$hash_element_value = $obj->h->{x}; # hash element value
$hash_element_value = $obj->h (x); # same thing
$obj->h->{x} = new value; # assign to hash element
$obj->h (x, newer value); # same thing

# code type accessor:
$code_ref = $obj->x; # reference to code
$obj->x->(...); # call code
$obj->x (sub {...}); # assign to element

# regexp type accessor:
$regexp = $obj->r; # reference to code
$string =~ m/$obj->r/; # match regexp
$obj->r (qr/ ... /); # assign to element

# class type accessor:
$element_value = $obj->c; # object reference
$obj->c->method (...); # call method of object
$obj->c (My_Other_Class::->new); # assign a new object

Class::Struct::FIELDS exports a single function, struct. Given a list of element names and types, and optionally a class name and/or an array reference of base classes, struct creates a Perl 5 class that implements a "struct-like" data structure with inheritance.

The new class is given a constructor method, new, for creating struct objects.
Each element in the struct data has an accessor method, which is used to assign to the element and to fetch its value. The default accessor can be overridden by declaring a sub of the same name in the package. (See Example 2.)

Each elements type can be scalar, array, hash, code or class.

Class::Std is a Perl module to support for creating standard "inside-out" classes.

SYNOPSIS

package MyClass;
use Class::Std;

# Create storage for object attributes...
my %name : ATTR;
my %rank : ATTR;
my %snum : ATTR;

my %public_data : ATTR;

# Handle initialization of objects of this class...
sub BUILD {
my ($self, $obj_ID, $arg_ref) = @_;

$name{$obj_ID} = check_name( $arg_ref->{name} );
$rank{$obj_ID} = check_rank( $arg_ref->{rank} );
$snum{$obj_ID} = _gen_uniq_serial_num();
}

# Handle cleanup of objects of this class...
sub DEMOLISH {
my ($self, $obj_ID) = @_;

_recycle_serial_num( $snum{$obj_ID} );
}

# Handle unknown method calls...
sub AUTOMETHOD {
my ($self, $obj_ID, @other_args) = @_;

# Return any public data...
if ( m/A get_(.*)/ ) { # Method name passed in $_
my $get_what = $1;
return sub {
return $public_data{$obj_ID}{$get_what};
}
}

warn "Cant call $method_name on ", ref $self, " object";

return; # The call is declined by not returning a sub ref
}

This module provides tools that help to implement the "inside out object" class structure in a convenient and standard way.

Class::Classless is a Perl framework for classless OOP.

SYNOPSIS

use strict;
use Class::Classless;
my $ob1 = $Class::Classless::ROOT->clone;
$ob1->{NAME} = Ob1;
$ob1->{stuff} = 123;
$ob1->{Thing} = 789;

my $ob2 = $ob1->clone;
$ob2->{NAME} = Ob2;

printf "ob1 stuff: n", $ob1->{stuff};
printf "ob2 stuff: n", $ob2->{stuff};
printf "ob1 Thing: n", $ob1->{Thing};
printf "ob2 Thing: n", $ob2->{Thing};

$ob1->{METHODS}{zaz} = sub {
print "Zaz! on ", $_[0]{NAME}, "n";
};

$ob1->zaz;
$ob2->zaz;
$ob1->EXAMINE;
$ob2->EXAMINE;
This prints the following:
ob1 stuff: < 123 >
ob2 stuff: < 123 >
ob1 Thing: < 789 >
ob2 Thing: < >
Zaz! on Ob1
Zaz! on Ob2
< Class::Classless::X=HASH(0x200236f4) >
stuff, 123,
NAME, Ob1,
Thing, 789,
METHODS, { zaz, CODE(0x20068360) },
PARENTS, [ ROOT ],
< Class::Classless::X=HASH(0x2002cb48) >
stuff, 123,
NAME, Ob2,
METHODS, { },
PARENTS, [ Ob1 ],

In class-based OOP frameworks, methods are applicable to objects by virtue of objects belonging to classes that either provide those methods, or inherit them from classes that do.

In classless OOP frameworks (AKA delegation-and-prototypes frameworks), what methods an object is capable of is basically an attribute of that object. That is, in Perl terms: instead of methods being entries in the symbol table of the package/class the object belongs to, they are entries in a hash table inside the object. Inheritance is implemented not by having classes inheriting from other classes (via ISA lists), but by having objects inherit from other objects (via PARENTS lists).

In class-based OOP frameworks, you get new objects by calling constructors. In a classless framework, you get new objects by copying ("cloning") an existing object -- and the new clone becomes a child (inheritor) of the original object. (Where do you get the one original object? The language provides one, which has no parents, and which contains some general purpose methods like "clone".)