NAME
Class::MOP::Class - Class Meta Object
SYNOPSIS
# use this for introspection ...
package Foo;
sub meta { Class::MOP::Class->initialize(__PACKAGE__) }
# elsewhere in the code ...
# 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
$package_name
. - construct_class_instance ($package_name)
-
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 byinitialize
and should never be called from outside of that method really.
Object instance construction
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 method is entirely optional, it is up to you whether you want to use it or not.
- construct_instance (%params)
-
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.
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
$method
other than use Sub::Name to make sure it is tagged with the correct name, and therefore show up correctly in stack traces and such. - has_method ($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 (useUNIVERSAL::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 withuse 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
$method_name
. Similar tocompute_all_applicable_methods
it returns a list of HASH references with the following information; method name (which will always be the same as$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
- 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 (seeconstruct_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
$attribute_name
has will be removed from the class at this time. This will make these attributes somewhat inaccessable in previously created instances. But if you are crazy enough to do this at runtime, then you are crazy enough to deal with something like this :). - get_attribute_list
-
This returns a list of attribute names which are defined in the local class. If you want a list of all applicable attributes for a class, use the
compute_all_applicable_attributes
method. - compute_all_applicable_attributes
-
This will traverse the inheritance heirachy and return a list of HASH references for all the applicable attributes for this class. The HASH references will contain the following information; the attribute name, the class which the attribute is associated with and the actual attribute meta-object.
Package Variables
Since Perl's classes are built atop the Perl package system, it is fairly common to use package scoped variables for things like static class variables. The following methods are convience methods for the creation and inspection of package scoped variables.
- add_package_variable ($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.
This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.