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