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Class::MOP::Class(3)  User Contributed Perl Documentation Class::MOP::Class(3)

NAME
       Class::MOP::Class - Class Meta Object

VERSION
       version 2.0604

SYNOPSIS
	 # assuming that class Foo
	 # has been defined, you can

	 # 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' => (
		 version      => '0.01',
		 superclasses => ['Foo'],
		 attributes   => [
		     Class::MOP::Attribute->new('$bar'),
		     Class::MOP::Attribute->new('$baz'),
		 ],
		 methods => {
		     calculate_bar => sub {...},
		     construct_baz => sub {...}
		 }
	     )
	 );

DESCRIPTION
       The Class Protocol is the largest and most complex part of the
       Class::MOP meta-object protocol. It controls the introspection and
       manipulation of Perl 5 classes, and it can create them as well. The
       best way to understand what this module can do is to read the
       documentation for each of its methods.

INHERITANCE
       "Class::MOP::Class" is a subclass of Class::MOP::Module.

METHODS
   Class construction
       These methods all create new "Class::MOP::Class" objects. These objects
       can represent existing classes or they can be used to create new
       classes from scratch.

       The metaclass object for a given class is a singleton. If you attempt
       to create a metaclass for the same class twice, you will just get the
       existing object.

       Class::MOP::Class->create($package_name, %options)
	   This method creates a new "Class::MOP::Class" object with the given
	   package name. It accepts a number of options:

	   ·	   version

		   An optional version number for the newly created package.

	   ·	   authority

		   An optional authority for the newly created package.

	   ·	   superclasses

		   An optional array reference of superclass names.

	   ·	   methods

		   An optional hash reference of methods for the class. The
		   keys of the hash reference are method names and values are
		   subroutine references.

	   ·	   attributes

		   An optional array reference of Class::MOP::Attribute
		   objects.

	   ·	   meta_name

		   Specifies the name to install the "meta" method for this
		   class under.	 If it is not passed, "meta" is assumed, and
		   if "undef" is explicitly given, no meta method will be
		   installed.

	   ·	   weaken

		   If true, the metaclass that is stored in the global cache
		   will be a weak reference.

		   Classes created in this way are destroyed once the
		   metaclass they are attached to goes out of scope, and will
		   be removed from Perl's internal symbol table.

		   All instances of a class with a weakened metaclass keep a
		   special reference to the metaclass object, which prevents
		   the metaclass from going out of scope while any instances
		   exist.

		   This only works if the instance is based on a hash
		   reference, however.

       Class::MOP::Class->create_anon_class(%options)
	   This method works just like "Class::MOP::Class->create" but it
	   creates an "anonymous" class. In fact, the class does have a name,
	   but that name is a unique name generated internally by this module.

	   It accepts the same "superclasses", "methods", and "attributes"
	   parameters that "create" accepts.

	   Anonymous classes default to "weaken => 1", although this can be
	   overridden.

       Class::MOP::Class->initialize($package_name, %options)
	   This method will initialize a "Class::MOP::Class" object for the
	   named package. Unlike "create", this method will not create a new
	   class.

	   The purpose of this method is to retrieve a "Class::MOP::Class"
	   object for introspecting an existing class.

	   If an existing "Class::MOP::Class" object exists for the named
	   package, it will be returned, and any options provided will be
	   ignored!

	   If the object does not yet exist, it will be created.

	   The valid options that can be passed to this method are
	   "attribute_metaclass", "method_metaclass",
	   "wrapped_method_metaclass", and "instance_metaclass". These are all
	   optional, and default to the appropriate class in the "Class::MOP"
	   distribution.

   Object instance construction and cloning
       These methods are all related to creating and/or cloning object
       instances.

       $metaclass->clone_object($instance, %params)
	   This method clones an existing object instance. Any parameters you
	   provide are will override existing attribute values in the object.

	   This is a convenience method for cloning an object instance, then
	   blessing it into the appropriate package.

	   You could implement a clone method in your class, using this
	   method:

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

       $metaclass->rebless_instance($instance, %params)
	   This method changes the class of $instance to the metaclass's
	   class.

	   You can only rebless an instance into a subclass of its current
	   class. If you pass any additional parameters, these will be treated
	   like constructor parameters and used to initialize the object's
	   attributes. Any existing attributes that are already set will be
	   overwritten.

	   Before reblessing the instance, this method will call
	   "rebless_instance_away" on the instance's current metaclass. This
	   method will be passed the instance, the new metaclass, and any
	   parameters specified to "rebless_instance". By default,
	   "rebless_instance_away" does nothing; it is merely a hook.

       $metaclass->rebless_instance_back($instance)
	   Does the same thing as "rebless_instance", except that you can only
	   rebless an instance into one of its superclasses. Any attributes
	   that do not exist in the superclass will be deinitialized.

	   This is a much more dangerous operation than "rebless_instance",
	   especially when multiple inheritance is involved, so use this
	   carefully!

       $metaclass->new_object(%params)
	   This method is used to create a new object of the metaclass's
	   class. Any parameters you provide are used to initialize the
	   instance's attributes. A special "__INSTANCE__" key can be passed
	   to provide an already generated instance, rather than having
	   Class::MOP generate it for you. This is mostly useful for using
	   Class::MOP with foreign classes which generate instances using
	   their own constructors.

       $metaclass->instance_metaclass
	   Returns the class name of the instance metaclass. See
	   Class::MOP::Instance for more information on the instance
	   metaclass.

       $metaclass->get_meta_instance
	   Returns an instance of the "instance_metaclass" to be used in the
	   construction of a new instance of the class.

   Informational predicates
       These are a few predicate methods for asking information about the
       class itself.

       $metaclass->is_anon_class
	   This returns true if the class was created by calling
	   "Class::MOP::Class->create_anon_class".

       $metaclass->is_mutable
	   This returns true if the class is still mutable.

       $metaclass->is_immutable
	   This returns true if the class has been made immutable.

       $metaclass->is_pristine
	   A class is not pristine if it has non-inherited attributes or if it
	   has any generated methods.

   Inheritance Relationships
       $metaclass->superclasses(@superclasses)
	   This is a read-write accessor which represents the superclass
	   relationships of the metaclass's class.

	   This is basically sugar around getting and setting @ISA.

       $metaclass->class_precedence_list
	   This returns a list of all of the class's ancestor classes. The
	   classes are returned in method dispatch order.

       $metaclass->linearized_isa
	   This returns a list based on "class_precedence_list" but with all
	   duplicates removed.

       $metaclass->subclasses
	   This returns a list of all subclasses for this class, even indirect
	   subclasses.

       $metaclass->direct_subclasses
	   This returns a list of immediate subclasses for this class, which
	   does not include indirect subclasses.

   Method introspection and creation
       These methods allow you to introspect a class's methods, as well as
       add, remove, or change methods.

       Determining what is truly a method in a Perl 5 class requires some
       heuristics (aka guessing).

       Methods defined outside the package with a fully qualified name ("sub
       Package::name { ... }") will be included. Similarly, methods named with
       a fully qualified name using Sub::Name are also included.

       However, we attempt to ignore imported functions.

       Ultimately, we are using heuristics to determine what truly is a method
       in a class, and these heuristics may get the wrong answer in some edge
       cases. However, for most "normal" cases the heuristics work correctly.

       $metaclass->get_method($method_name)
	   This will return a Class::MOP::Method for the specified
	   $method_name. If the class does not have the specified method, it
	   returns "undef"

       $metaclass->has_method($method_name)
	   Returns a boolean indicating whether or not the class defines the
	   named method. It does not include methods inherited from parent
	   classes.

       $metaclass->get_method_list
	   This will return a list of method names for all methods defined in
	   this class.

       $metaclass->add_method($method_name, $method)
	   This method takes a method name and a subroutine reference, and
	   adds the method to the class.

	   The subroutine reference can be a Class::MOP::Method, and you are
	   strongly encouraged to pass a meta method object instead of a code
	   reference. If you do so, that object gets stored as part of the
	   class's method map directly. If not, the meta information will have
	   to be recreated later, and may be incorrect.

	   If you provide a method object, this method will clone that object
	   if the object's package name does not match the class name. This
	   lets us track the original source of any methods added from other
	   classes (notably Moose roles).

       $metaclass->remove_method($method_name)
	   Remove the named method from the class. This method returns the
	   Class::MOP::Method object for the method.

       $metaclass->method_metaclass
	   Returns the class name of the method metaclass, see
	   Class::MOP::Method for more information on the method metaclass.

       $metaclass->wrapped_method_metaclass
	   Returns the class name of the wrapped method metaclass, see
	   Class::MOP::Method::Wrapped for more information on the wrapped
	   method metaclass.

       $metaclass->get_all_methods
	   This will traverse the inheritance hierarchy and return a list of
	   all the Class::MOP::Method objects for this class and its parents.

       $metaclass->find_method_by_name($method_name)
	   This will return a Class::MOP::Method for the specified
	   $method_name. If the class does not have the specified method, it
	   returns "undef"

	   Unlike "get_method", this method will look for the named method in
	   superclasses.

       $metaclass->get_all_method_names
	   This will return a list of method names for all of this class's
	   methods, including inherited methods.

       $metaclass->find_all_methods_by_name($method_name)
	   This method looks for the named method in the class and all of its
	   parents. It returns every matching method it finds in the
	   inheritance tree, so it returns a list of methods.

	   Each method is returned as a hash reference with three keys. The
	   keys are "name", "class", and "code". The "code" key has a
	   Class::MOP::Method object as its value.

	   The list of methods is distinct.

       $metaclass->find_next_method_by_name($method_name)
	   This method returns the first method in any superclass matching the
	   given name. It is effectively the method that "SUPER::$method_name"
	   would dispatch to.

   Attribute introspection and creation
       Because Perl 5 does not have a core concept of attributes in classes,
       we can only return information about attributes which have been added
       via this class's methods. We cannot discover information about
       attributes which are defined in terms of "regular" Perl 5 methods.

       $metaclass->get_attribute($attribute_name)
	   This will return a Class::MOP::Attribute for the specified
	   $attribute_name. If the class does not have the specified
	   attribute, it returns "undef".

	   NOTE that get_attribute does not search superclasses, for that you
	   need to use "find_attribute_by_name".

       $metaclass->has_attribute($attribute_name)
	   Returns a boolean indicating whether or not the class defines the
	   named attribute. It does not include attributes inherited from
	   parent classes.

       $metaclass->get_attribute_list
	   This will return a list of attributes names for all attributes
	   defined in this class.  Note that this operates on the current
	   class only, it does not traverse the inheritance hierarchy.

       $metaclass->get_all_attributes
	   This will traverse the inheritance hierarchy and return a list of
	   all the Class::MOP::Attribute objects for this class and its
	   parents.

       $metaclass->find_attribute_by_name($attribute_name)
	   This will return a Class::MOP::Attribute for the specified
	   $attribute_name. If the class does not have the specified
	   attribute, it returns "undef".

	   Unlike "get_attribute", this attribute will look for the named
	   attribute in superclasses.

       $metaclass->add_attribute(...)
	   This method accepts either an existing Class::MOP::Attribute object
	   or parameters suitable for passing to that class's "new" method.

	   The attribute provided will be added to the class.

	   Any accessor methods defined by the attribute will be added to the
	   class when the attribute is added.

	   If an attribute of the same name already exists, the old attribute
	   will be removed first.

       $metaclass->remove_attribute($attribute_name)
	   This will remove the named attribute from the class, and
	   Class::MOP::Attribute object.

	   Removing an attribute also removes any accessor methods defined by
	   the attribute.

	   However, note that removing an attribute will only affect future
	   object instances created for this class, not existing instances.

       $metaclass->attribute_metaclass
	   Returns the class name of the attribute metaclass for this class.
	   By default, this is Class::MOP::Attribute.

   Overload introspection and creation
       These methods provide an API to the core overload functionality.

       $metaclass->is_overloaded
	   Returns true if overloading is enabled for this class. Corresponds
	   to overload::Overloaded.

       $metaclass->get_overloaded_operator($op)
	   Returns the Class::MOP::Method::Overload object corresponding to
	   the operator named $op, if one exists for this class.

       $metaclass->has_overloaded_operator($op)
	   Returns whether or not the operator $op is overloaded for this
	   class.

       $metaclass->get_overload_list
	   Returns a list of operator names which have been overloaded (see
	   "Overloadable Operations" in overload for the list of valid
	   operator names).

       $metaclass->get_all_overloaded_operators
	   Returns a list of Class::MOP::Method::Overload objects
	   corresponding to the operators that have been overloaded.

       $metaclass->add_overloaded_operator($op, $impl)
	   Overloads the operator $op for this class, with the implementation
	   $impl.  $impl can be either a coderef or a method name. Corresponds
	   to "use overload $op => $impl;"

       $metaclass->remove_overloaded_operator($op)
	   Remove overloading for operator $op. Corresponds to "no overload
	   $op;"

   Class Immutability
       Making a class immutable "freezes" the class definition. You can no
       longer call methods which alter the class, such as adding or removing
       methods or attributes.

       Making a class immutable lets us optimize the class by inlining some
       methods, and also allows us to optimize some methods on the metaclass
       object itself.

       After immutabilization, the metaclass object will cache most
       informational methods that returns information about methods or
       attributes. Methods which would alter the class, such as
       "add_attribute" and "add_method", will throw an error on an immutable
       metaclass object.

       The immutabilization system in Moose takes much greater advantage of
       the inlining features than Class::MOP itself does.

       $metaclass->make_immutable(%options)
	   This method will create an immutable transformer and use it to make
	   the class and its metaclass object immutable, and returns true (you
	   should not rely on the details of this value apart from its truth).

	   This method accepts the following options:

	   ·	   inline_accessors

	   ·	   inline_constructor

	   ·	   inline_destructor

		   These are all booleans indicating whether the specified
		   method(s) should be inlined.

		   By default, accessors and the constructor are inlined, but
		   not the destructor.

	   ·	   immutable_trait

		   The name of a class which will be used as a parent class
		   for the metaclass object being made immutable. This "trait"
		   implements the post-immutability functionality of the
		   metaclass (but not the transformation itself).

		   This defaults to Class::MOP::Class::Immutable::Trait.

	   ·	   constructor_name

		   This is the constructor method name. This defaults to
		   "new".

	   ·	   constructor_class

		   The name of the method metaclass for constructors. It will
		   be used to generate the inlined constructor. This defaults
		   to "Class::MOP::Method::Constructor".

	   ·	   replace_constructor

		   This is a boolean indicating whether an existing
		   constructor should be replaced when inlining a constructor.
		   This defaults to false.

	   ·	   destructor_class

		   The name of the method metaclass for destructors. It will
		   be used to generate the inlined destructor. This defaults
		   to "Class::MOP::Method::Denstructor".

	   ·	   replace_destructor

		   This is a boolean indicating whether an existing destructor
		   should be replaced when inlining a destructor. This
		   defaults to false.

       $metaclass->immutable_options
	   Returns a hash of the options used when making the class immutable,
	   including both defaults and anything supplied by the user in the
	   call to "$metaclass->make_immutable". This is useful if you need to
	   temporarily make a class mutable and then restore immutability as
	   it was before.

       $metaclass->make_mutable
	   Calling this method reverse the immutabilization transformation.

   Method Modifiers
       Method modifiers are hooks which allow a method to be wrapped with
       before, after and around method modifiers. Every time a method is
       called, its modifiers are also called.

       A class can modify its own methods, as well as methods defined in
       parent classes.

       How method modifiers work?

       Method modifiers work by wrapping the original method and then
       replacing it in the class's symbol table. The wrappers will handle
       calling all the modifiers in the appropriate order and preserving the
       calling context for the original method.

       The return values of "before" and "after" modifiers are ignored. This
       is because their purpose is not to filter the input and output of the
       primary method (this is done with an around modifier).

       This may seem like an odd restriction to some, but doing this allows
       for simple code to be added at the beginning or end of a method call
       without altering the function of the wrapped method or placing any
       extra responsibility on the code of the modifier.

       Of course if you have more complex needs, you can use the "around"
       modifier which allows you to change both the parameters passed to the
       wrapped method, as well as its return value.

       Before and around modifiers are called in last-defined-first-called
       order, while after modifiers are called in first-defined-first-called
       order. So the call tree might looks something like this:

	 before 2
	  before 1
	   around 2
	    around 1
	     primary
	    around 1
	   around 2
	  after 1
	 after 2

       What is the performance impact?

       Of course there is a performance cost associated with method modifiers,
       but we have made every effort to make that cost directly proportional
       to the number of modifier features you use.

       The wrapping method does its best to only do as much work as it
       absolutely needs to. In order to do this we have moved some of the
       performance costs to set-up time, where they are easier to amortize.

       All this said, our benchmarks have indicated the following:

	 simple wrapper with no modifiers	      100% slower
	 simple wrapper with simple before modifier   400% slower
	 simple wrapper with simple after modifier    450% slower
	 simple wrapper with simple around modifier   500-550% slower
	 simple wrapper with all 3 modifiers	      1100% slower

       These numbers may seem daunting, but you must remember, every feature
       comes with some cost. To put things in perspective, just doing a simple
       "AUTOLOAD" which does nothing but extract the name of the method called
       and return it costs about 400% over a normal method call.

       $metaclass->add_before_method_modifier($method_name, $code)
	   This wraps the specified method with the supplied subroutine
	   reference. The modifier will be called as a method itself, and will
	   receive the same arguments as are passed to the method.

	   When the modifier exits, the wrapped method will be called.

	   The return value of the modifier will be ignored.

       $metaclass->add_after_method_modifier($method_name, $code)
	   This wraps the specified method with the supplied subroutine
	   reference. The modifier will be called as a method itself, and will
	   receive the same arguments as are passed to the method.

	   When the wrapped methods exits, the modifier will be called.

	   The return value of the modifier will be ignored.

       $metaclass->add_around_method_modifier($method_name, $code)
	   This wraps the specified method with the supplied subroutine
	   reference.

	   The first argument passed to the modifier will be a subroutine
	   reference to the wrapped method. The second argument is the object,
	   and after that come any arguments passed when the method is called.

	   The around modifier can choose to call the original method, as well
	   as what arguments to pass if it does so.

	   The return value of the modifier is what will be seen by the
	   caller.

   Introspection
       Class::MOP::Class->meta
	   This will return a Class::MOP::Class instance for this class.

	   It should also be noted that Class::MOP will actually bootstrap
	   this module by installing a number of attribute meta-objects into
	   its metaclass.

AUTHOR
       Moose is maintained by the Moose Cabal, along with the help of many
       contributors. See "CABAL" in Moose and "CONTRIBUTORS" in Moose for
       details.

COPYRIGHT AND LICENSE
       This software is copyright (c) 2012 by Infinity Interactive, Inc..

       This is free software; you can redistribute it and/or modify it under
       the same terms as the Perl 5 programming language system itself.

perl v5.16.2			  2012-09-19		  Class::MOP::Class(3)
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