John Williams > Class-Classless-C3 > Class::Classless::C3



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Class::Classless::C3 - Classless object system framework


  use Class::Classless::C3;

  # create a new object
  my $a = Class::Classless::C3::ROOT->new('a');
  my $b = Class::Classless::C3->new('b');   # ROOT is default parent

  # create derived object
  my $c = $b->new('c');

  # attributes (not inherited) and methods (inherited)
  $b->{'attribute'} = 'exists';
  $b->meta->addmethod('method' => sub { "exists" });

  print $c->{'attribute'};  # ''
  print $c->method;         # 'exists'


This implements a classless object system, very similar to Class::Classless.

There are two major differences. One is that Class::Classless::C3 relies on Algorithm::C3 to determine the inheritance tree, which outsources the most complicated part of the code.

The more important difference is that there is no $callstate object passed around in Class::Classless::C3. This means methods can be written in exactly the same way methods are written in other perl objects. The job formerly done by $callstate is now accomplished using Sub::Name.

Classless Objects ^

As with Class::Classless, all objects are created by inheriting from a $ROOT object. Objects can have attributes (data members) which are not inherited, and can have methods added to them, which will be inherited by sub-objects.

A Class::Classless::C3 object is a blessed hash reference, so attributes are merely hash entries.

The only "special" hash key is called _meta, but you should use the meta accessor method. It contains a classless meta object which contains all the meta information for the class, including its name, parent(s), and methods. It is also used when altering the class meta information.


$obj2 = $obj->new( ['name'] )

Creates a new $obj2, with the given name, with $obj as the parent. This is like the 'clone' method from Class::Classless. If no name is given, and unique name will be autogenerated. It calls an 'init' method, which you can override for object initialization.


This is how to call the same method in the superclass. It will dispatch in C3 method resolution order.

It is similar to the use of SUPER:: in normal perl objects, and equivalent to next::method from Class::C3.

It is a no-op if the method does not exist in any superclass.

$obj->can( 'methodname' )

Checks whether an object (or its parents) can execute the given method, and returns a code reference for the method.

$obj->isa( $objn )

Returns true if $obj is a descendant of the argument, which can be an object or an object name. The 'can' method is more useful.


Should return a version number, if your object has one.


Returns the meta-object, used for altering the object meta-information, such as the object name, parent object(s), and adding methods.


$obj->meta->name( ['name'] )

Gets or sets the object's name.

$obj->meta->parent( [$obj2] )

Gets or sets the object's parent. This method only supports single inheritance.

$obj->meta->parents( [$obj3, $obj4, ...] )

Gets or sets multiple parents for an objects, in order to support multiple inheritance.

$obj->meta->addparent( $obj5 )

Adds another parent to the object. This is the most common method of setting up multiple inheritance.

$obj->meta->addmethod( 'mymethod' => sub { 'this is what i do' } )

Adds a new method to an object. Requires a method name and a code ref.

$obj->meta->delmethod( 'mymethod' )

Deletes a method from an object.

Miscellany ^

These are some extra features provided by Class::Classless::C3. I'm not sure why you would use them, but I found a use for them.


This is a convenience method to create a classless object from an existing perl package. The statement

  $parent = Package->Class::Classless::C3:Meta::declassify();

will create a classless object with all the methods defined in 'Package', which you could use as a parent for a lot of other generated classless objects. Mainly, it makes writing the code for the parent object more straight-forward and perlish.


If you assign a coderef to this variable, it will activate an autoload-like feature.

If $obj->method is called, and method does not exist, this autoload sub is called (with the object and methodname as arguments) it give it a chance to create the method. It should return a coderef on success, which will be called. It can also do $obj->meta->addmethod to avoid this overhead in the future.


If this is assigned to a scalar ref (not a scalar), every time a classless method or NEXT is called, debug information will be appended to the string.


All classless objects are blessed in to the Class::Classless:C3 namespace, so to determine if an object is classless, just ask whether ref($obj) eq 'Class::Classless::C3'

Algorithm::C3 will die on invalid inheritance trees. The algorithm used in Class::Classless would try anyway, not necessarily with sane results.


The original Class::Classless


John Williams,


Copyright (C) 2008-2010 by John Williams. All rights reserved.

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

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