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author | Lorry Tar Creator <lorry-tar-importer@lorry> | 2015-06-06 17:50:16 +0000 |
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committer | Lorry Tar Creator <lorry-tar-importer@lorry> | 2015-06-06 17:50:16 +0000 |
commit | 5ac2026f7eed78958d69d051e7a8e993dcf51205 (patch) | |
tree | 298c3d2f08bdfe5689998b11892d72a897985be1 /lib/Class/MOP.pm | |
download | Moose-tarball-5ac2026f7eed78958d69d051e7a8e993dcf51205.tar.gz |
Moose-2.1405HEADMoose-2.1405master
Diffstat (limited to 'lib/Class/MOP.pm')
-rw-r--r-- | lib/Class/MOP.pm | 1232 |
1 files changed, 1232 insertions, 0 deletions
diff --git a/lib/Class/MOP.pm b/lib/Class/MOP.pm new file mode 100644 index 0000000..e55527d --- /dev/null +++ b/lib/Class/MOP.pm @@ -0,0 +1,1232 @@ +package Class::MOP; +our $VERSION = '2.1405'; + +use strict; +use warnings; + +use 5.008003; + +use MRO::Compat; +use Class::Load 0.07 (); +use Scalar::Util 'weaken', 'isweak', 'blessed'; +use Data::OptList; + +use Class::MOP::Mixin::AttributeCore; +use Class::MOP::Mixin::HasAttributes; +use Class::MOP::Mixin::HasMethods; +use Class::MOP::Mixin::HasOverloads; +use Class::MOP::Class; +use Class::MOP::Attribute; +use Class::MOP::Method; + +BEGIN { + *IS_RUNNING_ON_5_10 = ($] < 5.009_005) + ? sub () { 0 } + : sub () { 1 }; + + # this is either part of core or set up appropriately by MRO::Compat + *check_package_cache_flag = \&mro::get_pkg_gen; +} + +XSLoader::load( + 'Moose', + $VERSION, +); + +{ + # Metaclasses are singletons, so we cache them here. + # there is no need to worry about destruction though + # because they should die only when the program dies. + # After all, do package definitions even get reaped? + # Anonymous classes manage their own destruction. + my %METAS; + + sub get_all_metaclasses { %METAS } + sub get_all_metaclass_instances { values %METAS } + sub get_all_metaclass_names { keys %METAS } + sub get_metaclass_by_name { $METAS{$_[0]} } + sub store_metaclass_by_name { $METAS{$_[0]} = $_[1] } + sub weaken_metaclass { weaken($METAS{$_[0]}) } + sub metaclass_is_weak { isweak($METAS{$_[0]}) } + sub does_metaclass_exist { exists $METAS{$_[0]} && defined $METAS{$_[0]} } + sub remove_metaclass_by_name { delete $METAS{$_[0]}; return } + + # This handles instances as well as class names + sub class_of { + return unless defined $_[0]; + my $class = blessed($_[0]) || $_[0]; + return $METAS{$class}; + } + + # NOTE: + # We only cache metaclasses, meaning instances of + # Class::MOP::Class. We do not cache instance of + # Class::MOP::Package or Class::MOP::Module. Mostly + # because I don't yet see a good reason to do so. +} + +sub load_class { + Class::MOP::Deprecated::deprecated( + message => 'Class::MOP::load_class is deprecated', + feature => 'Class::Load wrapper functions', + ); + require Class::Load; + goto &Class::Load::load_class; +} + +sub load_first_existing_class { + Class::MOP::Deprecated::deprecated( + message => 'Class::MOP::load_first_existing_class is deprecated', + feature => 'Class::Load wrapper functions', + ); + require Class::Load; + goto &Class::Load::load_first_existing_class; +} + +sub is_class_loaded { + Class::MOP::Deprecated::deprecated( + message => 'Class::MOP::is_class_loaded is deprecated', + feature => 'Class::Load wrapper functions', + ); + require Class::Load; + goto &Class::Load::is_class_loaded; +} + +sub _definition_context { + my %context; + @context{qw(package file line)} = caller(1); + + return ( + definition_context => \%context, + ); +} + +## ---------------------------------------------------------------------------- +## Setting up our environment ... +## ---------------------------------------------------------------------------- +## Class::MOP needs to have a few things in the global perl environment so +## that it can operate effectively. Those things are done here. +## ---------------------------------------------------------------------------- + +# ... nothing yet actually ;) + +## ---------------------------------------------------------------------------- +## Bootstrapping +## ---------------------------------------------------------------------------- +## The code below here is to bootstrap our MOP with itself. This is also +## sometimes called "tying the knot". By doing this, we make it much easier +## to extend the MOP through subclassing and such since now you can use the +## MOP itself to extend itself. +## +## Yes, I know, that's weird and insane, but it's a good thing, trust me :) +## ---------------------------------------------------------------------------- + +# We need to add in the meta-attributes here so that +# any subclass of Class::MOP::* will be able to +# inherit them using _construct_instance + +## -------------------------------------------------------- +## Class::MOP::Mixin::HasMethods + +Class::MOP::Mixin::HasMethods->meta->add_attribute( + Class::MOP::Attribute->new('_methods' => ( + reader => { + # NOTE: + # we just alias the original method + # rather than re-produce it here + '_method_map' => \&Class::MOP::Mixin::HasMethods::_method_map + }, + default => sub { {} }, + _definition_context(), + )) +); + +Class::MOP::Mixin::HasMethods->meta->add_attribute( + Class::MOP::Attribute->new('method_metaclass' => ( + reader => { + # NOTE: + # we just alias the original method + # rather than re-produce it here + 'method_metaclass' => \&Class::MOP::Mixin::HasMethods::method_metaclass + }, + default => 'Class::MOP::Method', + _definition_context(), + )) +); + +Class::MOP::Mixin::HasMethods->meta->add_attribute( + Class::MOP::Attribute->new('wrapped_method_metaclass' => ( + reader => { + # NOTE: + # we just alias the original method + # rather than re-produce it here + 'wrapped_method_metaclass' => \&Class::MOP::Mixin::HasMethods::wrapped_method_metaclass + }, + default => 'Class::MOP::Method::Wrapped', + _definition_context(), + )) +); + +## -------------------------------------------------------- +## Class::MOP::Mixin::HasAttributes + +Class::MOP::Mixin::HasAttributes->meta->add_attribute( + Class::MOP::Attribute->new('attributes' => ( + reader => { + # NOTE: we need to do this in order + # for the instance meta-object to + # not fall into meta-circular death + # + # we just alias the original method + # rather than re-produce it here + '_attribute_map' => \&Class::MOP::Mixin::HasAttributes::_attribute_map + }, + default => sub { {} }, + _definition_context(), + )) +); + +Class::MOP::Mixin::HasAttributes->meta->add_attribute( + Class::MOP::Attribute->new('attribute_metaclass' => ( + reader => { + # NOTE: + # we just alias the original method + # rather than re-produce it here + 'attribute_metaclass' => \&Class::MOP::Mixin::HasAttributes::attribute_metaclass + }, + default => 'Class::MOP::Attribute', + _definition_context(), + )) +); + +## -------------------------------------------------------- +## Class::MOP::Mixin::HasOverloads + +Class::MOP::Mixin::HasOverloads->meta->add_attribute( + Class::MOP::Attribute->new('_overload_map' => ( + reader => { + '_overload_map' => \&Class::MOP::Mixin::HasOverloads::_overload_map + }, + clearer => '_clear_overload_map', + default => sub { {} }, + _definition_context(), + )) +); + +## -------------------------------------------------------- +## Class::MOP::Package + +Class::MOP::Package->meta->add_attribute( + Class::MOP::Attribute->new('package' => ( + reader => { + # NOTE: we need to do this in order + # for the instance meta-object to + # not fall into meta-circular death + # + # we just alias the original method + # rather than re-produce it here + 'name' => \&Class::MOP::Package::name + }, + _definition_context(), + )) +); + +Class::MOP::Package->meta->add_attribute( + Class::MOP::Attribute->new('namespace' => ( + reader => { + # NOTE: + # we just alias the original method + # rather than re-produce it here + 'namespace' => \&Class::MOP::Package::namespace + }, + init_arg => undef, + default => sub { \undef }, + _definition_context(), + )) +); + +## -------------------------------------------------------- +## Class::MOP::Module + +# NOTE: +# yeah this is kind of stretching things a bit, +# but truthfully the version should be an attribute +# of the Module, the weirdness comes from having to +# stick to Perl 5 convention and store it in the +# $VERSION package variable. Basically if you just +# squint at it, it will look how you want it to look. +# Either as a package variable, or as a attribute of +# the metaclass, isn't abstraction great :) + +Class::MOP::Module->meta->add_attribute( + Class::MOP::Attribute->new('version' => ( + reader => { + # NOTE: + # we just alias the original method + # rather than re-produce it here + 'version' => \&Class::MOP::Module::version + }, + init_arg => undef, + default => sub { \undef }, + _definition_context(), + )) +); + +# NOTE: +# By following the same conventions as version here, +# we are opening up the possibility that people can +# use the $AUTHORITY in non-Class::MOP modules as +# well. + +Class::MOP::Module->meta->add_attribute( + Class::MOP::Attribute->new('authority' => ( + reader => { + # NOTE: + # we just alias the original method + # rather than re-produce it here + 'authority' => \&Class::MOP::Module::authority + }, + init_arg => undef, + default => sub { \undef }, + _definition_context(), + )) +); + +## -------------------------------------------------------- +## Class::MOP::Class + +Class::MOP::Class->meta->add_attribute( + Class::MOP::Attribute->new('superclasses' => ( + accessor => { + # NOTE: + # we just alias the original method + # rather than re-produce it here + 'superclasses' => \&Class::MOP::Class::superclasses + }, + init_arg => undef, + default => sub { \undef }, + _definition_context(), + )) +); + +Class::MOP::Class->meta->add_attribute( + Class::MOP::Attribute->new('instance_metaclass' => ( + reader => { + # NOTE: we need to do this in order + # for the instance meta-object to + # not fall into meta-circular death + # + # we just alias the original method + # rather than re-produce it here + 'instance_metaclass' => \&Class::MOP::Class::instance_metaclass + }, + default => 'Class::MOP::Instance', + _definition_context(), + )) +); + +Class::MOP::Class->meta->add_attribute( + Class::MOP::Attribute->new('immutable_trait' => ( + reader => { + 'immutable_trait' => \&Class::MOP::Class::immutable_trait + }, + default => "Class::MOP::Class::Immutable::Trait", + _definition_context(), + )) +); + +Class::MOP::Class->meta->add_attribute( + Class::MOP::Attribute->new('constructor_name' => ( + reader => { + 'constructor_name' => \&Class::MOP::Class::constructor_name, + }, + default => "new", + _definition_context(), + )) +); + +Class::MOP::Class->meta->add_attribute( + Class::MOP::Attribute->new('constructor_class' => ( + reader => { + 'constructor_class' => \&Class::MOP::Class::constructor_class, + }, + default => "Class::MOP::Method::Constructor", + _definition_context(), + )) +); + + +Class::MOP::Class->meta->add_attribute( + Class::MOP::Attribute->new('destructor_class' => ( + reader => { + 'destructor_class' => \&Class::MOP::Class::destructor_class, + }, + _definition_context(), + )) +); + +# NOTE: +# we don't actually need to tie the knot with +# Class::MOP::Class here, it is actually handled +# within Class::MOP::Class itself in the +# _construct_class_instance method. + +## -------------------------------------------------------- +## Class::MOP::Mixin::AttributeCore +Class::MOP::Mixin::AttributeCore->meta->add_attribute( + Class::MOP::Attribute->new('name' => ( + reader => { + # NOTE: we need to do this in order + # for the instance meta-object to + # not fall into meta-circular death + # + # we just alias the original method + # rather than re-produce it here + 'name' => \&Class::MOP::Mixin::AttributeCore::name + }, + _definition_context(), + )) +); + +Class::MOP::Mixin::AttributeCore->meta->add_attribute( + Class::MOP::Attribute->new('accessor' => ( + reader => { 'accessor' => \&Class::MOP::Mixin::AttributeCore::accessor }, + predicate => { 'has_accessor' => \&Class::MOP::Mixin::AttributeCore::has_accessor }, + _definition_context(), + )) +); + +Class::MOP::Mixin::AttributeCore->meta->add_attribute( + Class::MOP::Attribute->new('reader' => ( + reader => { 'reader' => \&Class::MOP::Mixin::AttributeCore::reader }, + predicate => { 'has_reader' => \&Class::MOP::Mixin::AttributeCore::has_reader }, + _definition_context(), + )) +); + +Class::MOP::Mixin::AttributeCore->meta->add_attribute( + Class::MOP::Attribute->new('initializer' => ( + reader => { 'initializer' => \&Class::MOP::Mixin::AttributeCore::initializer }, + predicate => { 'has_initializer' => \&Class::MOP::Mixin::AttributeCore::has_initializer }, + _definition_context(), + )) +); + +Class::MOP::Mixin::AttributeCore->meta->add_attribute( + Class::MOP::Attribute->new('definition_context' => ( + reader => { 'definition_context' => \&Class::MOP::Mixin::AttributeCore::definition_context }, + _definition_context(), + )) +); + +Class::MOP::Mixin::AttributeCore->meta->add_attribute( + Class::MOP::Attribute->new('writer' => ( + reader => { 'writer' => \&Class::MOP::Mixin::AttributeCore::writer }, + predicate => { 'has_writer' => \&Class::MOP::Mixin::AttributeCore::has_writer }, + _definition_context(), + )) +); + +Class::MOP::Mixin::AttributeCore->meta->add_attribute( + Class::MOP::Attribute->new('predicate' => ( + reader => { 'predicate' => \&Class::MOP::Mixin::AttributeCore::predicate }, + predicate => { 'has_predicate' => \&Class::MOP::Mixin::AttributeCore::has_predicate }, + _definition_context(), + )) +); + +Class::MOP::Mixin::AttributeCore->meta->add_attribute( + Class::MOP::Attribute->new('clearer' => ( + reader => { 'clearer' => \&Class::MOP::Mixin::AttributeCore::clearer }, + predicate => { 'has_clearer' => \&Class::MOP::Mixin::AttributeCore::has_clearer }, + _definition_context(), + )) +); + +Class::MOP::Mixin::AttributeCore->meta->add_attribute( + Class::MOP::Attribute->new('builder' => ( + reader => { 'builder' => \&Class::MOP::Mixin::AttributeCore::builder }, + predicate => { 'has_builder' => \&Class::MOP::Mixin::AttributeCore::has_builder }, + _definition_context(), + )) +); + +Class::MOP::Mixin::AttributeCore->meta->add_attribute( + Class::MOP::Attribute->new('init_arg' => ( + reader => { 'init_arg' => \&Class::MOP::Mixin::AttributeCore::init_arg }, + predicate => { 'has_init_arg' => \&Class::MOP::Mixin::AttributeCore::has_init_arg }, + _definition_context(), + )) +); + +Class::MOP::Mixin::AttributeCore->meta->add_attribute( + Class::MOP::Attribute->new('default' => ( + # default has a custom 'reader' method ... + predicate => { 'has_default' => \&Class::MOP::Mixin::AttributeCore::has_default }, + _definition_context(), + )) +); + +Class::MOP::Mixin::AttributeCore->meta->add_attribute( + Class::MOP::Attribute->new('insertion_order' => ( + reader => { 'insertion_order' => \&Class::MOP::Mixin::AttributeCore::insertion_order }, + writer => { '_set_insertion_order' => \&Class::MOP::Mixin::AttributeCore::_set_insertion_order }, + predicate => { 'has_insertion_order' => \&Class::MOP::Mixin::AttributeCore::has_insertion_order }, + _definition_context(), + )) +); + +## -------------------------------------------------------- +## Class::MOP::Attribute +Class::MOP::Attribute->meta->add_attribute( + Class::MOP::Attribute->new('associated_class' => ( + reader => { + # NOTE: we need to do this in order + # for the instance meta-object to + # not fall into meta-circular death + # + # we just alias the original method + # rather than re-produce it here + 'associated_class' => \&Class::MOP::Attribute::associated_class + }, + _definition_context(), + )) +); + +Class::MOP::Attribute->meta->add_attribute( + Class::MOP::Attribute->new('associated_methods' => ( + reader => { 'associated_methods' => \&Class::MOP::Attribute::associated_methods }, + default => sub { [] }, + _definition_context(), + )) +); + +Class::MOP::Attribute->meta->add_method('clone' => sub { + my $self = shift; + $self->meta->clone_object($self, @_); +}); + +## -------------------------------------------------------- +## Class::MOP::Method +Class::MOP::Method->meta->add_attribute( + Class::MOP::Attribute->new('body' => ( + reader => { 'body' => \&Class::MOP::Method::body }, + _definition_context(), + )) +); + +Class::MOP::Method->meta->add_attribute( + Class::MOP::Attribute->new('associated_metaclass' => ( + reader => { 'associated_metaclass' => \&Class::MOP::Method::associated_metaclass }, + _definition_context(), + )) +); + +Class::MOP::Method->meta->add_attribute( + Class::MOP::Attribute->new('package_name' => ( + reader => { 'package_name' => \&Class::MOP::Method::package_name }, + _definition_context(), + )) +); + +Class::MOP::Method->meta->add_attribute( + Class::MOP::Attribute->new('name' => ( + reader => { 'name' => \&Class::MOP::Method::name }, + _definition_context(), + )) +); + +Class::MOP::Method->meta->add_attribute( + Class::MOP::Attribute->new('original_method' => ( + reader => { 'original_method' => \&Class::MOP::Method::original_method }, + writer => { '_set_original_method' => \&Class::MOP::Method::_set_original_method }, + _definition_context(), + )) +); + +## -------------------------------------------------------- +## Class::MOP::Method::Wrapped + +# NOTE: +# the way this item is initialized, this +# really does not follow the standard +# practices of attributes, but we put +# it here for completeness +Class::MOP::Method::Wrapped->meta->add_attribute( + Class::MOP::Attribute->new('modifier_table' => ( + _definition_context(), + )) +); + +## -------------------------------------------------------- +## Class::MOP::Method::Generated + +Class::MOP::Method::Generated->meta->add_attribute( + Class::MOP::Attribute->new('is_inline' => ( + reader => { 'is_inline' => \&Class::MOP::Method::Generated::is_inline }, + default => 0, + _definition_context(), + )) +); + +Class::MOP::Method::Generated->meta->add_attribute( + Class::MOP::Attribute->new('definition_context' => ( + reader => { 'definition_context' => \&Class::MOP::Method::Generated::definition_context }, + _definition_context(), + )) +); + + +## -------------------------------------------------------- +## Class::MOP::Method::Inlined + +Class::MOP::Method::Inlined->meta->add_attribute( + Class::MOP::Attribute->new('_expected_method_class' => ( + reader => { '_expected_method_class' => \&Class::MOP::Method::Inlined::_expected_method_class }, + _definition_context(), + )) +); + +## -------------------------------------------------------- +## Class::MOP::Method::Accessor + +Class::MOP::Method::Accessor->meta->add_attribute( + Class::MOP::Attribute->new('attribute' => ( + reader => { + 'associated_attribute' => \&Class::MOP::Method::Accessor::associated_attribute + }, + _definition_context(), + )) +); + +Class::MOP::Method::Accessor->meta->add_attribute( + Class::MOP::Attribute->new('accessor_type' => ( + reader => { 'accessor_type' => \&Class::MOP::Method::Accessor::accessor_type }, + _definition_context(), + )) +); + +## -------------------------------------------------------- +## Class::MOP::Method::Constructor + +Class::MOP::Method::Constructor->meta->add_attribute( + Class::MOP::Attribute->new('options' => ( + reader => { + 'options' => \&Class::MOP::Method::Constructor::options + }, + default => sub { +{} }, + _definition_context(), + )) +); + +Class::MOP::Method::Constructor->meta->add_attribute( + Class::MOP::Attribute->new('associated_metaclass' => ( + init_arg => "metaclass", # FIXME alias and rename + reader => { + 'associated_metaclass' => \&Class::MOP::Method::Constructor::associated_metaclass + }, + _definition_context(), + )) +); + +## -------------------------------------------------------- +## Class::MOP::Overload + +Class::MOP::Overload->meta->add_attribute( + Class::MOP::Attribute->new( + 'operator' => ( + reader => { 'operator' => \&Class::MOP::Overload::operator }, + required => 1, + _definition_context(), + ) + ) +); + +for my $attr (qw( method_name coderef coderef_package coderef_name method )) { + Class::MOP::Overload->meta->add_attribute( + Class::MOP::Attribute->new( + $attr => ( + reader => { $attr => Class::MOP::Overload->can($attr) }, + predicate => { + 'has_' + . $attr => Class::MOP::Overload->can( 'has_' . $attr ) + }, + _definition_context(), + ) + ) + ); +} + +Class::MOP::Overload->meta->add_attribute( + Class::MOP::Attribute->new( + 'associated_metaclass' => ( + reader => { + 'associated_metaclass' => + \&Class::MOP::Overload::associated_metaclass + }, + _definition_context(), + ) + ) +); + +## -------------------------------------------------------- +## Class::MOP::Instance + +# NOTE: +# these don't yet do much of anything, but are just +# included for completeness + +Class::MOP::Instance->meta->add_attribute( + Class::MOP::Attribute->new('associated_metaclass', + reader => { associated_metaclass => \&Class::MOP::Instance::associated_metaclass }, + _definition_context(), + ), +); + +Class::MOP::Instance->meta->add_attribute( + Class::MOP::Attribute->new('_class_name', + init_arg => undef, + reader => { _class_name => \&Class::MOP::Instance::_class_name }, + #lazy => 1, # not yet supported by Class::MOP but out our version does it anyway + #default => sub { $_[0]->associated_metaclass->name }, + _definition_context(), + ), +); + +Class::MOP::Instance->meta->add_attribute( + Class::MOP::Attribute->new('attributes', + reader => { attributes => \&Class::MOP::Instance::get_all_attributes }, + _definition_context(), + ), +); + +Class::MOP::Instance->meta->add_attribute( + Class::MOP::Attribute->new('slots', + reader => { slots => \&Class::MOP::Instance::slots }, + _definition_context(), + ), +); + +Class::MOP::Instance->meta->add_attribute( + Class::MOP::Attribute->new('slot_hash', + reader => { slot_hash => \&Class::MOP::Instance::slot_hash }, + _definition_context(), + ), +); + +## -------------------------------------------------------- +## Class::MOP::Object + +# need to replace the meta method there with a real meta method object +Class::MOP::Object->meta->_add_meta_method('meta'); + +## -------------------------------------------------------- +## Class::MOP::Mixin + +# need to replace the meta method there with a real meta method object +Class::MOP::Mixin->meta->_add_meta_method('meta'); + +require Class::MOP::Deprecated unless our $no_deprecated; + +# we need the meta instance of the meta instance to be created now, in order +# for the constructor to be able to use it +Class::MOP::Instance->meta->get_meta_instance; + +# pretend the add_method never happened. it hasn't yet affected anything +undef Class::MOP::Instance->meta->{_package_cache_flag}; + +## -------------------------------------------------------- +## Now close all the Class::MOP::* classes + +# NOTE: we don't need to inline the accessors this only lengthens the compile +# time of the MOP, and gives us no actual benefits. + +$_->meta->make_immutable( + inline_constructor => 0, + constructor_name => "_new", + inline_accessors => 0, +) for qw/ + Class::MOP::Package + Class::MOP::Module + Class::MOP::Class + + Class::MOP::Attribute + Class::MOP::Method + Class::MOP::Instance + + Class::MOP::Object + + Class::MOP::Method::Generated + Class::MOP::Method::Inlined + + Class::MOP::Method::Accessor + Class::MOP::Method::Constructor + Class::MOP::Method::Wrapped + + Class::MOP::Method::Meta + + Class::MOP::Overload +/; + +$_->meta->make_immutable( + inline_constructor => 0, + constructor_name => undef, + inline_accessors => 0, +) for qw/ + Class::MOP::Mixin + Class::MOP::Mixin::AttributeCore + Class::MOP::Mixin::HasAttributes + Class::MOP::Mixin::HasMethods + Class::MOP::Mixin::HasOverloads +/; + +1; + +# ABSTRACT: A Meta Object Protocol for Perl 5 + +__END__ + +=pod + +=encoding UTF-8 + +=head1 NAME + +Class::MOP - A Meta Object Protocol for Perl 5 + +=head1 VERSION + +version 2.1405 + +=head1 DESCRIPTION + +This module is a fully functioning meta object protocol for the +Perl 5 object system. It makes no attempt to change the behavior or +characteristics of the Perl 5 object system, only to create a +protocol for its manipulation and introspection. + +That said, it does attempt to create the tools for building a rich set +of extensions to the Perl 5 object system. Every attempt has been made +to abide by the spirit of the Perl 5 object system that we all know +and love. + +This documentation is sparse on conceptual details. We suggest looking +at the items listed in the L<SEE ALSO> section for more +information. In particular the book "The Art of the Meta Object +Protocol" was very influential in the development of this system. + +=head2 What is a Meta Object Protocol? + +A meta object protocol is an API to an object system. + +To be more specific, it abstracts the components of an object system +(classes, object, methods, object attributes, etc.). These +abstractions can then be used to inspect and manipulate the object +system which they describe. + +It can be said that there are two MOPs for any object system; the +implicit MOP and the explicit MOP. The implicit MOP handles things +like method dispatch or inheritance, which happen automatically as +part of how the object system works. The explicit MOP typically +handles the introspection/reflection features of the object system. + +All object systems have implicit MOPs. Without one, they would not +work. Explicit MOPs are much less common, and depending on the +language can vary from restrictive (Reflection in Java or C#) to wide +open (CLOS is a perfect example). + +=head2 Yet Another Class Builder! Why? + +This is B<not> a class builder so much as a I<class builder +B<builder>>. The intent is that an end user will not use this module +directly, but instead this module is used by module authors to build +extensions and features onto the Perl 5 object system. + +This system is used by L<Moose>, which supplies a powerful class +builder system built entirely on top of C<Class::MOP>. + +=head2 Who is this module for? + +This module is for anyone who has ever created or wanted to create a +module for the Class:: namespace. The tools which this module provides +make doing complex Perl 5 wizardry simpler, by removing such barriers +as the need to hack symbol tables, or understand the fine details of +method dispatch. + +=head2 What changes do I have to make to use this module? + +This module was designed to be as unobtrusive as possible. Many of its +features are accessible without B<any> change to your existing +code. It is meant to be a complement to your existing code and not an +intrusion on your code base. Unlike many other B<Class::> modules, +this module B<does not> require you subclass it, or even that you +C<use> it in within your module's package. + +The only features which require additions to your code are the +attribute handling and instance construction features, and these are +both completely optional features. The only reason for this is because +Perl 5's object system does not actually have these features built +in. More information about this feature can be found below. + +=head2 About Performance + +It is a common misconception that explicit MOPs are a performance hit. +This is not a universal truth, it is a side-effect of some specific +implementations. For instance, using Java reflection is slow because +the JVM cannot take advantage of any compiler optimizations, and the +JVM has to deal with much more runtime type information as well. + +Reflection in C# is marginally better as it was designed into the +language and runtime (the CLR). In contrast, CLOS (the Common Lisp +Object System) was built to support an explicit MOP, and so +performance is tuned for it. + +This library in particular does its absolute best to avoid putting +B<any> drain at all upon your code's performance. In fact, by itself +it does nothing to affect your existing code. So you only pay for what +you actually use. + +=head2 About Metaclass compatibility + +This module makes sure that all metaclasses created are both upwards +and downwards compatible. The topic of metaclass compatibility is +highly esoteric and is something only encountered when doing deep and +involved metaclass hacking. There are two basic kinds of metaclass +incompatibility; upwards and downwards. + +Upwards metaclass compatibility means that the metaclass of a +given class is either the same as (or a subclass of) all of the +metaclasses of the class's ancestors. + +Downward metaclass compatibility means that the metaclasses of a +given class's ancestors are all the same as (or a subclass of) that +class's metaclass. + +Here is a diagram showing a set of two classes (C<A> and C<B>) and +two metaclasses (C<Meta::A> and C<Meta::B>) which have correct +metaclass compatibility both upwards and downwards. + + +---------+ +---------+ + | Meta::A |<----| Meta::B | <....... (instance of ) + +---------+ +---------+ <------- (inherits from) + ^ ^ + : : + +---------+ +---------+ + | A |<----| B | + +---------+ +---------+ + +In actuality, I<all> of a class's metaclasses must be compatible, +not just the class metaclass. That includes the instance, attribute, +and method metaclasses, as well as the constructor and destructor +classes. + +C<Class::MOP> will attempt to fix some simple types of +incompatibilities. If all the metaclasses for the parent class are +I<subclasses> of the child's metaclasses then we can simply replace +the child's metaclasses with the parent's. In addition, if the child +is missing a metaclass that the parent has, we can also just make the +child use the parent's metaclass. + +As I said this is a highly esoteric topic and one you will only run +into if you do a lot of subclassing of L<Class::MOP::Class>. If you +are interested in why this is an issue see the paper I<Uniform and +safe metaclass composition> linked to in the L<SEE ALSO> section of +this document. + +=head2 Using custom metaclasses + +Always use the L<metaclass> pragma when using a custom metaclass, this +will ensure the proper initialization order and not accidentally +create an incorrect type of metaclass for you. This is a very rare +problem, and one which can only occur if you are doing deep metaclass +programming. So in other words, don't worry about it. + +Note that if you're using L<Moose> we encourage you to I<not> use the +L<metaclass> pragma, and instead use L<Moose::Util::MetaRole> to apply +roles to a class's metaclasses. This topic is covered at length in +various L<Moose::Cookbook> recipes. + +=head1 PROTOCOLS + +The meta-object protocol is divided into 4 main sub-protocols: + +=head2 The Class protocol + +This provides a means of manipulating and introspecting a Perl 5 +class. It handles symbol table hacking for you, and provides a rich +set of methods that go beyond simple package introspection. + +See L<Class::MOP::Class> for more details. + +=head2 The Attribute protocol + +This provides a consistent representation for an attribute of a Perl 5 +class. Since there are so many ways to create and handle attributes in +Perl 5 OO, the Attribute protocol provide as much of a unified +approach as possible. Of course, you are always free to extend this +protocol by subclassing the appropriate classes. + +See L<Class::MOP::Attribute> for more details. + +=head2 The Method protocol + +This provides a means of manipulating and introspecting methods in the +Perl 5 object system. As with attributes, there are many ways to +approach this topic, so we try to keep it pretty basic, while still +making it possible to extend the system in many ways. + +See L<Class::MOP::Method> for more details. + +=head2 The Instance protocol + +This provides a layer of abstraction for creating object instances. +Since the other layers use this protocol, it is relatively easy to +change the type of your instances from the default hash reference to +some other type of reference. Several examples are provided in the +F<examples/> directory included in this distribution. + +See L<Class::MOP::Instance> for more details. + +=head1 FUNCTIONS + +Note that this module does not export any constants or functions. + +=head2 Utility functions + +Note that these are all called as B<functions, not methods>. + +=over 4 + +=item B<Class::MOP::get_code_info($code)> + +This function returns two values, the name of the package the C<$code> +is from and the name of the C<$code> itself. This is used by several +elements of the MOP to determine where a given C<$code> reference is +from. + +=item B<Class::MOP::class_of($instance_or_class_name)> + +This will return the metaclass of the given instance or class name. If the +class lacks a metaclass, no metaclass will be initialized, and C<undef> will be +returned. + +You should almost certainly be using +L<C<Moose::Util::find_meta>|Moose::Util/find_meta> instead. + +=back + +=head2 Metaclass cache functions + +C<Class::MOP> holds a cache of metaclasses. The following are functions +(B<not methods>) which can be used to access that cache. It is not +recommended that you mess with these. Bad things could happen, but if +you are brave and willing to risk it: go for it! + +=over 4 + +=item B<Class::MOP::get_all_metaclasses> + +This will return a hash of all the metaclass instances that have +been cached by L<Class::MOP::Class>, keyed by the package name. + +=item B<Class::MOP::get_all_metaclass_instances> + +This will return a list of all the metaclass instances that have +been cached by L<Class::MOP::Class>. + +=item B<Class::MOP::get_all_metaclass_names> + +This will return a list of all the metaclass names that have +been cached by L<Class::MOP::Class>. + +=item B<Class::MOP::get_metaclass_by_name($name)> + +This will return a cached L<Class::MOP::Class> instance, or nothing +if no metaclass exists with that C<$name>. + +=item B<Class::MOP::store_metaclass_by_name($name, $meta)> + +This will store a metaclass in the cache at the supplied C<$key>. + +=item B<Class::MOP::weaken_metaclass($name)> + +In rare cases (e.g. anonymous metaclasses) it is desirable to +store a weakened reference in the metaclass cache. This +function will weaken the reference to the metaclass stored +in C<$name>. + +=item B<Class::MOP::metaclass_is_weak($name)> + +Returns true if the metaclass for C<$name> has been weakened +(via C<weaken_metaclass>). + +=item B<Class::MOP::does_metaclass_exist($name)> + +This will return true of there exists a metaclass stored in the +C<$name> key, and return false otherwise. + +=item B<Class::MOP::remove_metaclass_by_name($name)> + +This will remove the metaclass stored in the C<$name> key. + +=back + +Some utility functions (such as C<Class::MOP::load_class>) that were +previously defined in C<Class::MOP> regarding loading of classes have been +extracted to L<Class::Load>. Please see L<Class::Load> for documentation. + +=head1 SEE ALSO + +=head2 Books + +There are very few books out on Meta Object Protocols and Metaclasses +because it is such an esoteric topic. The following books are really +the only ones I have found. If you know of any more, B<I<please>> +email me and let me know, I would love to hear about them. + +=over 4 + +=item I<The Art of the Meta Object Protocol> + +=item I<Advances in Object-Oriented Metalevel Architecture and Reflection> + +=item I<Putting MetaClasses to Work> + +=item I<Smalltalk: The Language> + +=back + +=head2 Papers + +=over 4 + +=item "Uniform and safe metaclass composition" + +An excellent paper by the people who brought us the original Traits paper. +This paper is on how Traits can be used to do safe metaclass composition, +and offers an excellent introduction section which delves into the topic of +metaclass compatibility. + +L<http://scg.unibe.ch/archive/papers/Duca05ySafeMetaclassTrait.pdf> + +=item "Safe Metaclass Programming" + +This paper seems to precede the above paper, and propose a mix-in based +approach as opposed to the Traits based approach. Both papers have similar +information on the metaclass compatibility problem space. + +L<http://citeseer.ist.psu.edu/37617.html> + +=back + +=head2 Prior Art + +=over 4 + +=item The Perl 6 MetaModel work in the Pugs project + +=over 4 + +=item L<http://svn.openfoundry.org/pugs/misc/Perl-MetaModel/> + +=item L<http://github.com/perl6/p5-modules/tree/master/Perl6-ObjectSpace/> + +=back + +=back + +=head2 Articles + +=over 4 + +=item CPAN Module Review of Class::MOP + +L<http://www.oreillynet.com/onlamp/blog/2006/06/cpan_module_review_classmop.html> + +=back + +=head1 SIMILAR MODULES + +As I have said above, this module is a class-builder-builder, so it is +not the same thing as modules like L<Class::Accessor> and +L<Class::MethodMaker>. That being said there are very few modules on CPAN +with similar goals to this module. The one I have found which is most +like this module is L<Class::Meta>, although its philosophy and the MOP it +creates are very different from this modules. + +=head1 BUGS + +All complex software has bugs lurking in it, and this module is no +exception. + +Please report any bugs to C<bug-class-mop@rt.cpan.org>, or through the +web interface at L<http://rt.cpan.org>. + +You can also discuss feature requests or possible bugs on the Moose +mailing list (moose@perl.org) or on IRC at +L<irc://irc.perl.org/#moose>. + +=head1 ACKNOWLEDGEMENTS + +=over 4 + +=item Rob Kinyon + +Thanks to Rob for actually getting the development of this module kick-started. + +=back + +=head1 AUTHORS + +=over 4 + +=item * + +Stevan Little <stevan.little@iinteractive.com> + +=item * + +Dave Rolsky <autarch@urth.org> + +=item * + +Jesse Luehrs <doy@tozt.net> + +=item * + +Shawn M Moore <code@sartak.org> + +=item * + +יובל קוג'מן (Yuval Kogman) <nothingmuch@woobling.org> + +=item * + +Karen Etheridge <ether@cpan.org> + +=item * + +Florian Ragwitz <rafl@debian.org> + +=item * + +Hans Dieter Pearcey <hdp@weftsoar.net> + +=item * + +Chris Prather <chris@prather.org> + +=item * + +Matt S Trout <mst@shadowcat.co.uk> + +=back + +=head1 COPYRIGHT AND LICENSE + +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. + +=cut |