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Class-MOP-0.10
River stage zero No dependents
2 ++
/ Class::MOP::Class

NAME

Class::MOP::Class - Class Meta Object

SYNOPSIS

  # use this for introspection ...
  
  # add a method to Foo ...
  Foo->meta->add_method('bar' => sub { ... })
  
  # get a list of all the classes searched 
  # the method dispatcher in the correct order 
  Foo->meta->class_precedence_list()
  
  # remove a method from Foo
  Foo->meta->remove_method('bar');
  
  # or use this to actually create classes ...
  
  Class::MOP::Class->create('Bar' => '0.01' => (
      superclasses => [ 'Foo' ],
      attributes => [
          Class::MOP:::Attribute->new('$bar'),
          Class::MOP:::Attribute->new('$baz'),          
      ],
      methods => {
          calculate_bar => sub { ... },
          construct_baz => sub { ... }          
      }
  ));

DESCRIPTION

This is the largest and currently most complex part of the Perl 5 meta-object protocol. It controls the introspection and manipulation of Perl 5 classes (and it can create them too). The best way to understand what this module can do, is to read the documentation for each of it's methods.

METHODS

Self Introspection

meta

This will return a Class::MOP::Class instance which is related to this class. Thereby allowing Class::MOP::Class to actually introspect itself.

As with Class::MOP::Attribute, Class::MOP will actually bootstrap this module by installing a number of attribute meta-objects into it's metaclass. This will allow this class to reap all the benifits of the MOP when subclassing it.

Class construction

These methods will handle creating Class::MOP::Class objects, which can be used to both create new classes, and analyze pre-existing classes.

This module will internally store references to all the instances you create with these methods, so that they do not need to be created any more than nessecary. Basically, they are singletons.

create ($package_name, ?$package_version, superclasses => ?@superclasses, methods => ?%methods, attributes => ?%attributes)

This returns a Class::MOP::Class object, bringing the specified $package_name into existence and adding any of the $package_version, @superclasses, %methods and %attributes to it.

initialize ($package_name)

This initializes and returns returns a Class::MOP::Class object for a given a $package_name.

construct_class_instance (%options)

This will construct an instance of Class::MOP::Class, it is here so that we can actually "tie the knot" for Class::MOP::Class to use construct_instance once all the bootstrapping is done. This method is used internally by initialize and should never be called from outside of that method really.

check_metaclass_compatability

This method is called as the very last thing in the construct_class_instance method. This will check that the metaclass you are creating is compatible with the metaclasses of all your ancestors. For more inforamtion about metaclass compatibility see the About Metaclass compatibility section in Class::MOP.

Object instance construction and cloning

These methods are entirely optional, it is up to you whether you want to use them or not.

new_object (%params)

This is a convience method for creating a new object of the class, and blessing it into the appropriate package as well. Ideally your class would call a new this method like so:

  sub MyClass::new { 
      my ($class, %param) = @_;
      $class->meta->new_object(%params);
  }

Of course the ideal place for this would actually be in UNIVERSAL:: but that is considered bad style, so we do not do that.

construct_instance (%params)

This method is used to construct an instace structure suitable for bless-ing into your package of choice. It works in conjunction with the Attribute protocol to collect all applicable attributes.

This will construct and instance using a HASH ref as storage (currently only HASH references are supported). This will collect all the applicable attributes and layout out the fields in the HASH ref, it will then initialize them using either use the corresponding key in %params or any default value or initializer found in the attribute meta-object.

clone_object ($instance, %params)

This is a convience method for cloning an object instance, then blessing it into the appropriate package. Ideally your class would call a clone this method like so:

  sub MyClass::clone {
      my ($self, %param) = @_;
      $self->meta->clone_object($self, %params);
  }

Of course the ideal place for this would actually be in UNIVERSAL:: but that is considered bad style, so we do not do that.

clone_instance($instance, %params)

This method is a compliment of construct_instance (which means if you override construct_instance, you need to override this one too).

This method will clone the $instance structure created by the construct_instance method, and apply any %params passed to it to change the attribute values. The structure returned is (like with construct_instance) an unblessed HASH reference, it is your responsibility to then bless this cloned structure into the right class.

Informational

name

This is a read-only attribute which returns the package name for the given Class::MOP::Class instance.

version

This is a read-only attribute which returns the $VERSION of the package for the given Class::MOP::Class instance.

Inheritance Relationships

superclasses (?@superclasses)

This is a read-write attribute which represents the superclass relationships of the class the Class::MOP::Class instance is associated with. Basically, it can get and set the @ISA for you.

NOTE: Perl will occasionally perform some @ISA and method caching, if you decide to change your superclass relationship at runtime (which is quite insane and very much not recommened), then you should be aware of this and the fact that this module does not make any attempt to address this issue.

class_precedence_list

This computes the a list of all the class's ancestors in the same order in which method dispatch will be done. This is similair to what Class::ISA::super_path does, but we don't remove duplicate names.

Methods

method_metaclass
add_method ($method_name, $method)

This will take a $method_name and CODE reference to that $method and install it into the class's package.

NOTE: This does absolutely nothing special to $method other than use Sub::Name to make sure it is tagged with the correct name, and therefore show up correctly in stack traces and such.

alias_method ($method_name, $method)

This will take a $method_name and CODE reference to that $method and alias the method into the class's package.

NOTE: Unlike add_method, this will not try to name the $method using Sub::Name, it only aliases the method in the class's package.

has_method ($method_name)

This just provides a simple way to check if the class implements a specific $method_name. It will not however, attempt to check if the class inherits the method (use UNIVERSAL::can for that).

This will correctly handle functions defined outside of the package that use a fully qualified name (sub Package::name { ... }).

This will correctly handle functions renamed with Sub::Name and installed using the symbol tables. However, if you are naming the subroutine outside of the package scope, you must use the fully qualified name, including the package name, for has_method to correctly identify it.

This will attempt to correctly ignore functions imported from other packages using Exporter. It breaks down if the function imported is an __ANON__ sub (such as with use constant), which very well may be a valid method being applied to the class.

In short, this method cannot always be trusted to determine if the $method_name is actually a method. However, it will DWIM about 90% of the time, so it's a small trade off I think.

get_method ($method_name)

This will return a CODE reference of the specified $method_name, or return undef if that method does not exist.

remove_method ($method_name)

This will attempt to remove a given $method_name from the class. It will return the CODE reference that it has removed, and will attempt to use Sub::Name to clear the methods associated name.

get_method_list

This will return a list of method names for all locally defined methods. It does not provide a list of all applicable methods, including any inherited ones. If you want a list of all applicable methods, use the compute_all_applicable_methods method.

compute_all_applicable_methods

This will return a list of all the methods names this class will respond to, taking into account inheritance. The list will be a list of HASH references, each one containing the following information; method name, the name of the class in which the method lives and a CODE reference for the actual method.

find_all_methods_by_name ($method_name)

This will traverse the inheritence hierarchy and locate all methods with a given $method_name. Similar to compute_all_applicable_methods it returns a list of HASH references with the following information; method name (which will always be the same as $method_name), the name of the class in which the method lives and a CODE reference for the actual method.

The list of methods produced is a distinct list, meaning there are no duplicates in it. This is especially useful for things like object initialization and destruction where you only want the method called once, and in the correct order.

Attributes

It should be noted that since there is no one consistent way to define the attributes of a class in Perl 5. These methods can only work with the information given, and can not easily discover information on their own. See Class::MOP::Attribute for more details.

attribute_metaclass
get_attribute_map
add_attribute ($attribute_name, $attribute_meta_object)

This stores a $attribute_meta_object in the Class::MOP::Class instance associated with the given class, and associates it with the $attribute_name. Unlike methods, attributes within the MOP are stored as meta-information only. They will be used later to construct instances from (see construct_instance above). More details about the attribute meta-objects can be found in the Class::MOP::Attribute or the "The Attribute protocol" in Class::MOP section.

It should be noted that any accessor, reader/writer or predicate methods which the $attribute_meta_object has will be installed into the class at this time.

has_attribute ($attribute_name)

Checks to see if this class has an attribute by the name of $attribute_name and returns a boolean.

get_attribute ($attribute_name)

Returns the attribute meta-object associated with $attribute_name, if none is found, it will return undef.

remove_attribute ($attribute_name)

This will remove the attribute meta-object stored at $attribute_name, then return the removed attribute meta-object.

NOTE: Removing an attribute will only affect future instances of the class, it will not make any attempt to remove the attribute from any existing instances of the class.

It should be noted that any accessor, reader/writer or predicate methods which the attribute meta-object stored at $attribute_name has will be removed from the class at this time. This will make these attributes somewhat inaccessable in previously created instances. But if you are crazy enough to do this at runtime, then you are crazy enough to deal with something like this :).

get_attribute_list

This returns a list of attribute names which are defined in the local class. If you want a list of all applicable attributes for a class, use the compute_all_applicable_attributes method.

compute_all_applicable_attributes

This will traverse the inheritance heirachy and return a list of all the applicable attributes for this class. It does not construct a HASH reference like compute_all_applicable_methods because all that same information is discoverable through the attribute meta-object itself.

Package Variables

Since Perl's classes are built atop the Perl package system, it is fairly common to use package scoped variables for things like static class variables. The following methods are convience methods for the creation and inspection of package scoped variables.

add_package_variable ($variable_name, ?$initial_value)

Given a $variable_name, which must contain a leading sigil, this method will create that variable within the package which houses the class. It also takes an optional $initial_value, which must be a reference of the same type as the sigil of the $variable_name implies.

get_package_variable ($variable_name)

This will return a reference to the package variable in $variable_name.

has_package_variable ($variable_name)

Returns true (1) if there is a package variable defined for $variable_name, and false (0) otherwise.

remove_package_variable ($variable_name)

This will attempt to remove the package variable at $variable_name.

AUTHOR

Stevan Little <stevan@iinteractive.com>

COPYRIGHT AND LICENSE

Copyright 2006 by Infinity Interactive, Inc.

http://www.iinteractive.com

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