use strict;
use warnings;
-use Scalar::Util 'blessed';
+use 5.008;
-our $VERSION = '0.01';
+use MRO::Compat;
-my %METAS;
-sub UNIVERSAL::meta {
- my $class = blessed($_[0]) || $_[0];
- $METAS{$class} ||= Class::MOP::Class->initialize($class)
+use Carp 'confess';
+use Scalar::Util 'weaken';
+
+
+use Class::MOP::Class;
+use Class::MOP::Attribute;
+use Class::MOP::Method;
+
+use Class::MOP::Immutable;
+
+BEGIN {
+ *IS_RUNNING_ON_5_10 = ($] < 5.009_005)
+ ? sub () { 0 }
+ : sub () { 1 };
+
+ *HAVE_ISAREV = defined(&mro::get_isarev)
+ ? sub () { 1 }
+ : sub () { 1 };
+
+ # this is either part of core or set up appropriately by MRO::Compat
+ *check_package_cache_flag = \&mro::get_pkg_gen;
}
-1;
+our $VERSION = '0.70_01';
+our $XS_VERSION = $VERSION;
+$VERSION = eval $VERSION;
+our $AUTHORITY = 'cpan:STEVAN';
+
+# after that everything is loaded, if we're allowed try to load faster XS
+# versions of various things
+_try_load_xs() or _load_pure_perl();
+
+sub _try_load_xs {
+ return if $ENV{CLASS_MOP_NO_XS};
+
+ my $e = do {
+ local $@;
+ eval {
+ require XSLoader;
+ # just doing this - no warnings 'redefine' - doesn't work
+ # for some reason
+ local $^W = 0;
+ __PACKAGE__->XSLoader::load($XS_VERSION);
+
+ require Sub::Name;
+ Sub::Name->import(qw(subname));
+
+ require Devel::GlobalDestruction;
+ Devel::GlobalDestruction->import("in_global_destruction");
+ };
+ $@;
+ };
+
+ die $e if $e && $e !~ /object version|loadable object/;
+
+ return $e ? 0 : 1;
+}
-__END__
+sub _load_pure_perl {
+ require Sub::Identify;
+ Sub::Identify->import('get_code_info');
-=pod
+ *subname = sub { $_[1] };
+ *in_global_destruction = sub () { !1 }
+}
-=head1 NAME
-Class::MOP - A Meta Object Protocol for Perl 5
+{
+ # 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?
+ my %METAS;
+
+ # means of accessing all the metaclasses that have
+ # been initialized thus far (for mugwumps obj browser)
+ 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 does_metaclass_exist { exists $METAS{$_[0]} && defined $METAS{$_[0]} }
+ sub remove_metaclass_by_name { $METAS{$_[0]} = undef }
+
+ # 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.
+}
-=head1 SYNOPSIS
+sub load_first_existing_class {
+ my @classes = @_
+ or return;
+
+ foreach my $class (@classes) {
+ unless ( _is_valid_class_name($class) ) {
+ my $display = defined($class) ? $class : 'undef';
+ confess "Invalid class name ($display)";
+ }
+ }
+
+ my $found;
+ my %exceptions;
+ for my $class (@classes) {
+ my $e = _try_load_one_class($class);
+
+ if ($e) {
+ $exceptions{$class} = $e;
+ }
+ else {
+ $found = $class;
+ last;
+ }
+ }
+
+ return $found if $found;
+
+ confess join(
+ "\n",
+ map {
+ sprintf(
+ "Could not load class (%s) because : %s", $_,
+ $exceptions{$_}
+ )
+ } @classes
+ );
+}
- # ... coming soon
+sub _try_load_one_class {
+ my $class = shift;
-=head1 DESCRIPTON
+ return if is_class_loaded($class);
-This module is an attempt to create a 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.
+ my $file = $class . '.pm';
+ $file =~ s{::}{/}g;
-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 for these tools to keep to the spirit of the Perl 5 object
-system that we all know and love.
+ return do {
+ local $@;
+ eval { require($file) };
+ $@;
+ };
+}
-=head2 Who is this module for?
+sub load_class {
+ my $class = load_first_existing_class($_[0]);
+ return get_metaclass_by_name($class) || $class;
+}
-This module is specifically for anyone who has ever created or
-wanted to create a module for the Class:: namespace. The tools which
-this module will provide will hopefully make it easier to do more
-complex things with Perl 5 classes by removing such barriers as
-the need to hack the symbol tables, or understand the fine details
-of method dispatch.
+sub _is_valid_class_name {
+ my $class = shift;
-=head1 PROTOCOLS
+ return 0 if ref($class);
+ return 0 unless defined($class);
+ return 0 unless length($class);
-The protocol is divided into 3 main sub-protocols:
+ return 1 if $class =~ /^\w+(?:::\w+)*$/;
-=over 4
+ return 0;
+}
-=item The Class protocol
+sub is_class_loaded {
+ my $class = shift;
-This provides a means of manipulating and introspecting a Perl 5
-class. It handles all of symbol table hacking for you, and provides
-a rich set of methods that go beyond simple package introspection.
+ return 0 if ref($class) || !defined($class) || !length($class);
-=item The Attribute protocol
+ # walk the symbol table tree to avoid autovififying
+ # \*{${main::}{"Foo::"}} == \*main::Foo::
-This provides a consistent represenation for an attribute of a
-Perl 5 class. Since there are so many ways to create and handle
-atttributes in Perl 5 OO, this attempts to provide as much of a
-unified approach as possible, while giving the freedom and
-flexibility to subclass for specialization.
+ my $pack = \*::;
+ foreach my $part (split('::', $class)) {
+ return 0 unless exists ${$$pack}{"${part}::"};
+ $pack = \*{${$$pack}{"${part}::"}};
+ }
-=item The Method protocol
+ # check for $VERSION or @ISA
+ return 1 if exists ${$$pack}{VERSION}
+ && defined *{${$$pack}{VERSION}}{SCALAR};
+ return 1 if exists ${$$pack}{ISA}
+ && defined *{${$$pack}{ISA}}{ARRAY};
-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.
+ # check for any method
+ foreach ( keys %{$$pack} ) {
+ next if substr($_, -2, 2) eq '::';
-=back
+ my $glob = ${$$pack}{$_} || next;
-What follows is a more detailed documentation on each specific sub
-protocol.
+ # constant subs
+ if ( IS_RUNNING_ON_5_10 ) {
+ return 1 if ref $glob eq 'SCALAR';
+ }
-=head2 The Class protocol
+ return 1 if defined *{$glob}{CODE};
+ }
-=head3 Class construction
+ # fail
+ return 0;
+}
-These methods handle creating Class objects, which can be used to
-both create new classes, and analyze pre-existing ones.
-Class::MOP will internally store weakened references to all the
-instances you create with these methods, so that they do not need
-to be created any more than nessecary.
+## ----------------------------------------------------------------------------
+## 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, thats 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::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
+ },
+ ))
+);
+
+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 }
+ ))
+);
+
+## --------------------------------------------------------
+## 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 }
+ ))
+);
+
+# 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 }
+ ))
+);
+
+## --------------------------------------------------------
+## Class::MOP::Class
+
+Class::MOP::Class->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
+ 'get_attribute_map' => \&Class::MOP::Class::get_attribute_map
+ },
+ default => sub { {} }
+ ))
+);
+
+Class::MOP::Class->meta->add_attribute(
+ Class::MOP::Attribute->new('methods' => (
+ reader => {
+ # NOTE:
+ # we just alias the original method
+ # rather than re-produce it here
+ 'get_method_map' => \&Class::MOP::Class::get_method_map
+ },
+ default => sub { {} }
+ ))
+);
+
+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 }
+ ))
+);
+
+Class::MOP::Class->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::Class::attribute_metaclass
+ },
+ default => 'Class::MOP::Attribute',
+ ))
+);
+
+Class::MOP::Class->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::Class::method_metaclass
+ },
+ default => 'Class::MOP::Method',
+ ))
+);
+
+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',
+ ))
+);
+
+# 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::Attribute
+
+Class::MOP::Attribute->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::Attribute::name
+ }
+ ))
+);
+
+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
+ }
+ ))
+);
+
+Class::MOP::Attribute->meta->add_attribute(
+ Class::MOP::Attribute->new('accessor' => (
+ reader => { 'accessor' => \&Class::MOP::Attribute::accessor },
+ predicate => { 'has_accessor' => \&Class::MOP::Attribute::has_accessor },
+ ))
+);
+
+Class::MOP::Attribute->meta->add_attribute(
+ Class::MOP::Attribute->new('reader' => (
+ reader => { 'reader' => \&Class::MOP::Attribute::reader },
+ predicate => { 'has_reader' => \&Class::MOP::Attribute::has_reader },
+ ))
+);
+
+Class::MOP::Attribute->meta->add_attribute(
+ Class::MOP::Attribute->new('initializer' => (
+ reader => { 'initializer' => \&Class::MOP::Attribute::initializer },
+ predicate => { 'has_initializer' => \&Class::MOP::Attribute::has_initializer },
+ ))
+);
+
+Class::MOP::Attribute->meta->add_attribute(
+ Class::MOP::Attribute->new('writer' => (
+ reader => { 'writer' => \&Class::MOP::Attribute::writer },
+ predicate => { 'has_writer' => \&Class::MOP::Attribute::has_writer },
+ ))
+);
+
+Class::MOP::Attribute->meta->add_attribute(
+ Class::MOP::Attribute->new('predicate' => (
+ reader => { 'predicate' => \&Class::MOP::Attribute::predicate },
+ predicate => { 'has_predicate' => \&Class::MOP::Attribute::has_predicate },
+ ))
+);
+
+Class::MOP::Attribute->meta->add_attribute(
+ Class::MOP::Attribute->new('clearer' => (
+ reader => { 'clearer' => \&Class::MOP::Attribute::clearer },
+ predicate => { 'has_clearer' => \&Class::MOP::Attribute::has_clearer },
+ ))
+);
+
+Class::MOP::Attribute->meta->add_attribute(
+ Class::MOP::Attribute->new('builder' => (
+ reader => { 'builder' => \&Class::MOP::Attribute::builder },
+ predicate => { 'has_builder' => \&Class::MOP::Attribute::has_builder },
+ ))
+);
+
+Class::MOP::Attribute->meta->add_attribute(
+ Class::MOP::Attribute->new('init_arg' => (
+ reader => { 'init_arg' => \&Class::MOP::Attribute::init_arg },
+ predicate => { 'has_init_arg' => \&Class::MOP::Attribute::has_init_arg },
+ ))
+);
+
+Class::MOP::Attribute->meta->add_attribute(
+ Class::MOP::Attribute->new('default' => (
+ # default has a custom 'reader' method ...
+ predicate => { 'has_default' => \&Class::MOP::Attribute::has_default },
+ ))
+);
+
+Class::MOP::Attribute->meta->add_attribute(
+ Class::MOP::Attribute->new('associated_methods' => (
+ reader => { 'associated_methods' => \&Class::MOP::Attribute::associated_methods },
+ default => sub { [] }
+ ))
+);
+
+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 },
+ ))
+);
+
+Class::MOP::Method->meta->add_attribute(
+ Class::MOP::Attribute->new('associated_metaclass' => (
+ reader => { 'associated_metaclass' => \&Class::MOP::Method::associated_metaclass },
+ ))
+);
+
+Class::MOP::Method->meta->add_attribute(
+ Class::MOP::Attribute->new('package_name' => (
+ reader => { 'package_name' => \&Class::MOP::Method::package_name },
+ ))
+);
+
+Class::MOP::Method->meta->add_attribute(
+ Class::MOP::Attribute->new('name' => (
+ reader => { 'name' => \&Class::MOP::Method::name },
+ ))
+);
+
+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 },
+ ))
+);
+
+Class::MOP::Method->meta->add_method('clone' => sub {
+ my $self = shift;
+ my $clone = $self->meta->clone_object($self, @_);
+ $clone->_set_original_method($self);
+ return $clone;
+});
+
+## --------------------------------------------------------
+## 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')
+);
+
+## --------------------------------------------------------
+## 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,
+ ))
+);
+
+## --------------------------------------------------------
+## 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
+ },
+ ))
+);
+
+Class::MOP::Method::Accessor->meta->add_attribute(
+ Class::MOP::Attribute->new('accessor_type' => (
+ reader => { 'accessor_type' => \&Class::MOP::Method::Accessor::accessor_type },
+ ))
+);
+
+## --------------------------------------------------------
+## 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 { +{} }
+ ))
+);
+
+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
+ },
+ ))
+);
+
+## --------------------------------------------------------
+## 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 },
+ ),
+);
+
+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 { $_[0]->associated_metaclass->name },
+ ),
+);
+
+Class::MOP::Instance->meta->add_attribute(
+ Class::MOP::Attribute->new('attributes',
+ reader => { attributes => \&Class::MOP::Instance::get_all_attributes },
+ ),
+);
+
+Class::MOP::Instance->meta->add_attribute(
+ Class::MOP::Attribute->new('slots',
+ reader => { slots => \&Class::MOP::Instance::slots },
+ ),
+);
+
+Class::MOP::Instance->meta->add_attribute(
+ Class::MOP::Attribute->new('slot_hash',
+ reader => { slot_hash => \&Class::MOP::Instance::slot_hash },
+ ),
+);
+
+
+# we need the meta instance of the meta instance to be created now, in order
+# for the constructor to be able to use it
+Class::MOP::Instance->meta->get_meta_instance;
+
+# pretend the add_method never happenned. it hasn't yet affected anything
+undef Class::MOP::Instance->meta->{_package_cache_flag};
+
+## --------------------------------------------------------
+## Now close all the Class::MOP::* classes
+
+# NOTE:
+# we don't need to inline the
+# constructors or the accessors
+# this only lengthens the compile
+# time of the MOP, and gives us
+# no actual benefits.
+
+$_->meta->make_immutable(
+ inline_constructor => 1,
+ replace_constructor => 1,
+ 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::Accessor
+ Class::MOP::Method::Constructor
+ Class::MOP::Method::Wrapped
+/;
-=over 4
+1;
-=item B<create ($package_name, ?$package_version,
- superclasses => ?@superclasses,
- methods => ?%methods,
- attributes => ?%attributes)>
+__END__
-This returns the basic Class object, bringing the specified
-C<$package_name> into existence and adding any of the
-C<$package_version>, C<@superclasses>, C<%methods> and C<%attributes>
-to it.
+=pod
-=item B<initialize ($package_name)>
+=head1 NAME
-This initializes a Class object for a given a C<$package_name>.
+Class::MOP - A Meta Object Protocol for Perl 5
-=back
+=head1 DESCRIPTON
-=head3 Instance construction
+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.
-=over 4
+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 for these tools to keep to the spirit of the Perl 5 object
+system that we all know and love.
-=item B<construct_instance ($canidate, %params)>
+This documentation is admittedly sparse on details, as time permits
+I will try to improve them. For now, I suggest looking at the items
+listed in the L<SEE ALSO> section for more information. In particular
+the book "The Art of the Meta Object Protocol" was very influential
+in the development of this system.
-This will construct and instance using the C<$canidate> as storage
-(currently only HASH references are supported). This will collect all
-the applicable attribute meta-objects and layout out the fields in the
-C<$canidate>, it will then initialize them using either use the
-corresponding key in C<%params> or any default value or initializer
-found in the attribute meta-object.
+=head2 What is a Meta Object Protocol?
-=back
+A meta object protocol is an API to an object system.
+
+To be more specific, it is a set of abstractions of the components of
+an object system (typically things like; classes, object, methods,
+object attributes, etc.). These abstractions can then be used to both
+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. Explict MOPs however as 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 it is a I<class builder
+B<builder>>. My intent is that an end user does 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.
-=head3 Informational
+=head2 Who is this module for?
+
+This module is specifically for anyone who has ever created or
+wanted to create a module for the Class:: namespace. The tools which
+this module will provide will hopefully make it easier to do more
+complex things with Perl 5 classes by removing such barriers as
+the need to hack the 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 unintrusive as possible. Many of
+its features are accessible without B<any> change to your existsing
+code at all. It is meant to be a compliment 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 requires 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 A Note about Performance?
+
+It is a common misconception that explict MOPs are performance drains.
+But this is not a universal truth at all, it is an side-effect of
+specific implementations. For instance, using Java reflection is much
+slower 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 it's 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
+class's ancestors.
+
+Downward metaclass compatibility means that the metaclasses of a
+given class's anscestors are all either the same as (or a subclass
+of) that 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 |
+ +---------+ +---------+
+
+As I said this is a highly esoteric topic and one you will only run
+into if you do a lot of subclassing of B<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 metaclass pragma when using a custom metaclass, this
+will ensure the proper initialization order and not accidentely
+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.
+
+=head1 PROTOCOLS
+
+The protocol is divided into 4 main sub-protocols:
=over 4
-=item B<name>
+=item The Class protocol
+
+This provides a means of manipulating and introspecting a Perl 5
+class. It handles all of 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.
-This is a read-only attribute which returns the package name that
-the Class is stored in.
+=item The Attribute protocol
-=item B<version>
+This provides a consistent represenation for an attribute of a
+Perl 5 class. Since there are so many ways to create and handle
+attributes in Perl 5 OO, this attempts to provide as much of a
+unified approach as possible, while giving the freedom and
+flexibility to subclass for specialization.
-This is a read-only attribute which returns the C<$VERSION> of the
-package the Class is stored in.
+See L<Class::MOP::Attribute> for more details.
+
+=item 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.
+
+=item 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 ref to other
+types of references. Several examples are provided in the F<examples/>
+directory included in this distribution.
+
+See L<Class::MOP::Instance> for more details.
=back
-=head3 Inheritance Relationships
+=head1 FUNCTIONS
+
+=head2 Constants
=over 4
-=item B<superclasses (?@superclasses)>
+=item I<IS_RUNNING_ON_5_10>
-This is a read-write attribute which represents the superclass
-relationships of this Class. Basically, it can get and set the
-C<@ISA> for you.
+We set this constant depending on what version perl we are on, this
+allows us to take advantage of new 5.10 features and stay backwards
+compat.
-=item B<class_precedence_list>
+=item I<HAVE_ISAREV>
-This computes the a list of the Class's ancestors in the same order
-in which method dispatch will be done.
+Whether or not C<mro> provides C<get_isarev>, a much faster way to get all the
+subclasses of a certain class.
=back
-=head3 Methods
+=head2 Utility functions
+
+Note that these are all called as B<functions, not methods>.
=over 4
-=item B<add_method ($method_name, $method)>
+=item B<load_class ($class_name)>
+
+This will load a given C<$class_name> and if it does not have an
+already initialized metaclass, then it will intialize one for it.
+This function can be used in place of tricks like
+C<eval "use $module"> or using C<require>.
+
+=item B<is_class_loaded ($class_name)>
-This will take a C<$method_name> and CODE reference to that
-C<$method> and install it into the Class.
+This will return a boolean depending on if the C<$class_name> has
+been loaded.
-B<NOTE> : This does absolutely nothing special to C<$method>
-other than use B<Sub::Name> to make sure it is tagged with the
-correct name, and therefore show up correctly in stack traces and
-such.
+NOTE: This does a basic check of the symbol table to try and
+determine as best it can if the C<$class_name> is loaded, it
+is probably correct about 99% of the time.
-=item B<has_method ($method_name)>
+=item B<check_package_cache_flag ($pkg)>
-This just provides a simple way to check if the Class implements
-a specific C<$method_name>. It will I<not> however, attempt to check
-if the class inherits the method.
+B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
-This will correctly ignore functions imported from other packages,
-and will correctly handle functions defined outside of the package
-that use a fully qualified name (C<sub Package::name { ... }>). It
-will B<not> handle anon functions stored in the package using symbol
-tables, unless the anon function is first named using B<Sub::Name>.
-For instance, this will not return true with C<has_method>:
+This will return an integer that is managed by C<Class::MOP::Class>
+to determine if a module's symbol table has been altered.
- *{$pkg . '::' . $name} = sub { ... };
+In Perl 5.10 or greater, this flag is package specific. However in
+versions prior to 5.10, this will use the C<PL_sub_generation> variable
+which is not package specific.
-However, this will DWIM:
+=item B<get_code_info ($code)>
- my $full_name = $pkg . '::' . $name;
- my $sub = sub { ... };
- Sub::Name::subname($full_name, $sub);
- *{$full_name} = $sub;
+B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
-B<NOTE:> this code need not be so tedious, it is only this way to
-illustrate my point more clearly.
+This function returns two values, the name of the package the C<$code>
+is from and the name of the C<$code> itself. This is used by several
+elements of the MOP to detemine where a given C<$code> reference is from.
-=item B<get_method ($method_name)>
+=item B<subname ($name, $code)>
-This will return a CODE reference of the specified C<$method_name>,
-or return undef if that method does not exist.
+B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
-=item B<remove_method ($method_name)>
+If possible, we will load the L<Sub::Name> module and this will function
+as C<Sub::Name::subname> does, otherwise it will just return the C<$code>
+argument.
-This will attempt to remove a given C<$method_name> from the Class.
-It will return the CODE reference that it has removed, and will
-attempt to use B<Sub::Name> to clear the methods associated name.
+=item B<in_global_destruction>
-=item B<get_method_list>
+B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
-This will return a list of method names for all I<locally> defined
-methods. It does B<not> provide a list of all applicable methods,
-including any inherited ones. If you want a list of all applicable
-methods, use the C<compute_all_applicable_methods> method.
+If L<Devel::GlobalDestruction> is available, this returns true under global
+destruction.
-=item B<compute_all_applicable_methods>
+Otherwise it's a constant returning false.
-This will return a list of all the methods names this Class will
-support, taking into account inheritance. The list will be a list of
-HASH references, each one containing the following information; method
-name, the name of the class in which the method lives and a CODE
-reference for the actual method.
+=item B<load_first_existing_class ($class_name, [$class_name, ...])>
-=item B<find_all_methods_by_name ($method_name)>
+B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
-This will traverse the inheritence hierarchy and locate all methods
-with a given C<$method_name>. Similar to
-C<compute_all_applicable_methods> it returns a list of HASH references
-with the following information; method name (which will always be the
-same as C<$method_name>), the name of the class in which the method
-lives and a CODE reference for the actual method.
+Given a list of class names, this function will attempt to load each
+one in turn.
+
+If it finds a class it can load, it will return that class' name.
+If none of the classes can be loaded, it will throw an exception.
=back
-=head3 Attributes
+=head2 Metaclass cache functions
-It should be noted that since there is no one consistent way to define
-the attributes of a class in Perl 5. These methods can only work with
-the information given, and can not easily discover information on
-their own.
+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 this, bad things could happen. But if
+you are brave and willing to risk it, go for it.
=over 4
-=item B<add_attribute ($attribute_name, $attribute_meta_object)>
+=item B<get_all_metaclasses>
-This stores a C<$attribute_meta_object> in the Class object and
-associates it with the C<$attribute_name>. Unlike methods, attributes
-within the MOP are stored as meta-information only. They will be used
-later to construct instances from (see C<construct_instance> above).
-More details about the attribute meta-objects can be found in the
-L<The Attribute protocol> section of this document.
+This will return an hash of all the metaclass instances that have
+been cached by B<Class::MOP::Class> keyed by the package name.
-=item B<has_attribute ($attribute_name)>
+=item B<get_all_metaclass_instances>
-Checks to see if this Class has an attribute by the name of
-C<$attribute_name> and returns a boolean.
+This will return an array of all the metaclass instances that have
+been cached by B<Class::MOP::Class>.
-=item B<get_attribute ($attribute_name)>
+=item B<get_all_metaclass_names>
-Returns the attribute meta-object associated with C<$attribute_name>,
-if none is found, it will return undef.
+This will return an array of all the metaclass names that have
+been cached by B<Class::MOP::Class>.
-=item B<remove_attribute ($attribute_name)>
+=item B<get_metaclass_by_name ($name)>
-This will remove the attribute meta-object stored at
-C<$attribute_name>, then return the removed attribute meta-object.
+This will return a cached B<Class::MOP::Class> instance of nothing
+if no metaclass exist by that C<$name>.
-B<NOTE:> Removing an attribute will only affect future instances of
-the class, it will not make any attempt to remove the attribute from
-any existing instances of the class.
+=item B<store_metaclass_by_name ($name, $meta)>
-=item B<get_attribute_list>
+This will store a metaclass in the cache at the supplied C<$key>.
-This returns a list of attribute names which are defined in the local
-class. If you want a list of all applicable attributes for a class,
-use the C<compute_all_applicable_attributes> method.
+=item B<weaken_metaclass ($name)>
-=item B<compute_all_applicable_attributes>
+In rare cases it is desireable to store a weakened reference in
+the metaclass cache. This function will weaken the reference to
+the metaclass stored in C<$name>.
-This will traverse the inheritance heirachy and return a list of HASH
-references for all the applicable attributes for this class. The HASH
-references will contain the following information; the attribute name,
-the class which the attribute is associated with and the actual
-attribute meta-object
+=item B<does_metaclass_exist ($name)>
-=item B<create_all_accessors>
+This will return true of there exists a metaclass stored in the
+C<$name> key and return false otherwise.
-This will communicate with all of the classes attributes to create
-and install the appropriate accessors. (see L<The Attribute Protocol>
-below for more details).
+=item B<remove_metaclass_by_name ($name)>
-=back
+This will remove a the metaclass stored in the C<$name> key.
-=head2 The Attribute Protocol
+=back
-This protocol is almost entirely an invention of this module. This is
-because Perl 5 does not have consistent notion of what is an attribute
-of a class. There are so many ways in which this is done, and very few
-(if any) are discoverable by this module.
+=head1 SEE ALSO
-So, all that said, this module attempts to inject some order into this
-chaos, by introducing a more consistent approach.
+=head2 Books
-=head3 Creation
+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 B<new ($name, %accessor_description, $class_initialization_arg, $default_value)>
+=item "The Art of the Meta Object Protocol"
+
+=item "Advances in Object-Oriented Metalevel Architecture and Reflection"
+
+=item "Putting MetaClasses to Work"
- Class::MOP::Attribute->new('$foo' => (
- accessor => 'foo', # dual purpose get/set accessor
- init_arg => '-foo', # class->new will look for a -foo key
- default => 'BAR IS BAZ!' # if no -foo key is provided, use this
- ));
-
- Class::MOP::Attribute->new('$.bar' => (
- reader => 'bar', # getter
- writer => 'set_bar', # setter
- init_arg => '-bar', # class->new will look for a -bar key
- # no default value means it is undef
- ));
+=item "Smalltalk: The Language"
-=back
+=back
-=head3 Informational
+=head2 Papers
=over 4
-=item B<name>
+=item Uniform and safe metaclass composition
-=item B<accessor>
+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.
-=item B<reader>
+L<http://www.iam.unibe.ch/~scg/Archive/Papers/Duca05ySafeMetaclassTrait.pdf>
-=item B<writer>
+=item Safe Metaclass Programming
-=item B<init_arg>
+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.
-=item B<default>
+L<http://citeseer.ist.psu.edu/37617.html>
=back
-=head3 Informational predicates
+=head2 Prior Art
=over 4
-=item B<has_accessor>
+=item The Perl 6 MetaModel work in the Pugs project
-Returns true if this attribute uses a get/set accessor, and false
-otherwise
+=over 4
-=item B<has_reader>
+=item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel>
-Returns true if this attribute has a reader, and false otherwise
+=item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace>
-=item B<has_writer>
+=back
-Returns true if this attribute has a writer, and false otherwise
+=back
-=item B<has_init_arg>
+=head2 Articles
-Returns true if this attribute has a class intialization argument, and
-false otherwise
+=over 4
-=item B<has_default>
+=item CPAN Module Review of Class::MOP
-Returns true if this attribute has a default value, and false
-otherwise.
+L<http://www.oreillynet.com/onlamp/blog/2006/06/cpan_module_review_classmop.html>
=back
-=head3 Attribute Accessor generation
+=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 it's 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. If you find a bug please either email me, or add the bug
+to cpan-RT.
+
+=head1 ACKNOWLEDGEMENTS
=over 4
-=item B<generate_accessors>
+=item Rob Kinyon
-This allows the attribute to generate code for it's own accessor
-methods. This is mostly part of an internal protocol between the class
-and it's own attributes, see the C<create_all_accessors> method above.
+Thanks to Rob for actually getting the development of this module kick-started.
=back
-=head2 The Method Protocol
+=head1 AUTHORS
-This protocol is very small, since methods in Perl 5 are just
-subroutines within the particular package. Basically all we do is to
-bless the subroutine and provide some very simple introspection
-methods for it.
+Stevan Little E<lt>stevan@iinteractive.comE<gt>
-=head1 SEE ALSO
+B<with contributions from:>
-=over 4
+Brandon (blblack) Black
-=item "The Art of the Meta Object Protocol"
+Florian (rafl) Ragwitz
-=item "Advances in Object-Oriented Metalevel Architecture and Reflection"
+Guillermo (groditi) Roditi
-=back
+Matt (mst) Trout
+
+Rob (robkinyon) Kinyon
-=head1 AUTHOR
+Yuval (nothingmuch) Kogman
-Stevan Little E<gt>stevan@iinteractive.comE<lt>
+Scott (konobi) McWhirter
=head1 COPYRIGHT AND LICENSE
-Copyright 2006 by Infinity Interactive, Inc.
+Copyright 2006-2008 by Infinity Interactive, Inc.
L<http://www.iinteractive.com>
This library is free software; you can redistribute it and/or modify
-it under the same terms as Perl itself.
+it under the same terms as Perl itself.
=cut
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