Class::MOP::Class - Class Meta Object
version 2.2201
# 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 {...}
}
)
);
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.
Class::MOP::Class is a subclass of the Class::MOP::Module manpage.
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.
See authority in the Class::MOP::Module manpage for more details.
- 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 the Class::MOP::Attribute manpage 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.
It also accepts a cache option. If this is true , then the anonymous class
will be cached based on its superclasses and roles. If an existing anonymous
class in the cache has the same superclasses and roles, it will be reused.
Anonymous classes default to weaken => 1 if cache is false , 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.
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
the Class::MOP::Instance manpage 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.
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.
- $metaclass-
superclasses(@superclasses) >>$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.
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 the Sub::Util manpage 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 the Class::MOP::Method manpage 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 the Class::MOP::Method manpage, 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
the Class::MOP::Method manpage object for the method.
- $metaclass->method_metaclass
-
Returns the class name of the method metaclass, see
the Class::MOP::Method manpage for more information on the method metaclass.
- $metaclass->wrapped_method_metaclass
-
Returns the class name of the wrapped method metaclass, see
the Class::MOP::Method::Wrapped manpage 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 the Class::MOP::Method manpage objects for this class and its parents.
- $metaclass->find_method_by_name($method_name)
-
This will return a the Class::MOP::Method manpage 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
the Class::MOP::Method manpage 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.
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 the Class::MOP::Attribute manpage 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 the Class::MOP::Attribute manpage objects for this class and its parents.
- $metaclass->find_attribute_by_name($attribute_name)
-
This will return a the Class::MOP::Attribute manpage 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 the Class::MOP::Attribute manpage
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
the Class::MOP::Attribute manpage 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 the Class::MOP::Attribute manpage.
These methods provide an API to the core overload functionality.
- $metaclass->is_overloaded
-
Returns true if overloading is enabled for this class. Corresponds to
is_overloaded in the Devel::OverloadInfo manpage.
- $metaclass->get_overloaded_operator($op)
-
Returns the the Class::MOP::Overload manpage 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
overload/Overloadable Operations for the list of valid operator names).
- $metaclass->get_all_overloaded_operators
-
Returns a list of the Class::MOP::Overload manpage objects corresponding to the
operators that have been overloaded.
- $metaclass->add_overloaded_operator($op, $impl)
-
Overloads the operator
$op for this class. The $impl can be a coderef, a
method name, or a the Class::MOP::Overload manpage object. Corresponds to
use overload $op => $impl;
- $metaclass->remove_overloaded_operator($op)
-
Remove overloading for operator
$op . Corresponds to no overload $op;
- $metaclass->get_overload_fallback_value
-
Returns the overload
fallback setting for the package.
- $metaclass->set_overload_fallback_value($fallback)
-
Sets the overload
fallback setting for the package.
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 the Class::MOP::Class::Immutable::Trait manpage.
- 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 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.
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
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.
- Class::MOP::Class->meta
-
This will return a the Class::MOP::Class manpage instance for this class.
It should also be noted that the Class::MOP manpage will actually bootstrap
this module by installing a number of attribute meta-objects into its
metaclass.
This software is copyright (c) 2006 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.
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