use strict;
use warnings;
-use Scalar::Util 'blessed';
+use Carp 'confess';
+use Scalar::Util ();
+
+use Class::MOP::Class;
+use Class::MOP::Attribute;
+use Class::MOP::Method;
+
+use Class::MOP::Class::Immutable;
+
+our $VERSION = '0.31';
+
+## ----------------------------------------------------------------------------
+## Setting up our environment ...
+## ----------------------------------------------------------------------------
+## Class::MOP needs to have a few things in the global perl environment so
+## that it can operate effectively. Those things are done here.
+## ----------------------------------------------------------------------------
+
+# ... nothing yet actually ;)
+
+## ----------------------------------------------------------------------------
+## Bootstrapping
+## ----------------------------------------------------------------------------
+## The code below here is to bootstrap our MOP with itself. This is also
+## sometimes called "tying the knot". By doing this, we make it much easier
+## to extend the MOP through subclassing and such since now you can use the
+## MOP itself to extend itself.
+##
+## Yes, I know, thats weird and insane, but it's a good thing, trust me :)
+## ----------------------------------------------------------------------------
+
+# We need to add in the meta-attributes here so that
+# any subclass of Class::MOP::* will be able to
+# inherit them using &construct_instance
+
+## Class::MOP::Package
+
+Class::MOP::Package->meta->add_attribute(
+ Class::MOP::Attribute->new('$:package' => (
+ reader => {
+ # NOTE: we need to do this in order
+ # for the instance meta-object to
+ # not fall into meta-circular death
+ 'name' => sub { (shift)->{'$:package'} }
+ },
+ init_arg => ':package',
+ ))
+);
+
+## Class::MOP::Class
+
+Class::MOP::Class->meta->add_attribute(
+ Class::MOP::Attribute->new('%:attributes' => (
+ reader => {
+ # NOTE: we need to do this in order
+ # for the instance meta-object to
+ # not fall into meta-circular death
+ 'get_attribute_map' => sub { (shift)->{'%:attributes'} }
+ },
+ init_arg => ':attributes',
+ default => sub { {} }
+ ))
+);
+
+Class::MOP::Class->meta->add_attribute(
+ Class::MOP::Attribute->new('$:attribute_metaclass' => (
+ reader => 'attribute_metaclass',
+ init_arg => ':attribute_metaclass',
+ default => 'Class::MOP::Attribute',
+ ))
+);
+
+Class::MOP::Class->meta->add_attribute(
+ Class::MOP::Attribute->new('$:method_metaclass' => (
+ reader => 'method_metaclass',
+ init_arg => ':method_metaclass',
+ default => 'Class::MOP::Method',
+ ))
+);
+
+Class::MOP::Class->meta->add_attribute(
+ Class::MOP::Attribute->new('$:instance_metaclass' => (
+ reader => {
+ # NOTE: we need to do this in order
+ # for the instance meta-object to
+ # not fall into meta-circular death
+ 'instance_metaclass' => sub { (shift)->{'$:instance_metaclass'} }
+ },
+ init_arg => ':instance_metaclass',
+ default => 'Class::MOP::Instance',
+ ))
+);
+
+## 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
+ 'name' => sub { (shift)->{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
+ 'associated_class' => sub { (shift)->{associated_class} }
+ }
+ ))
+);
+
+Class::MOP::Attribute->meta->add_attribute(
+ Class::MOP::Attribute->new('accessor' => (
+ reader => 'accessor',
+ predicate => 'has_accessor',
+ ))
+);
+
+Class::MOP::Attribute->meta->add_attribute(
+ Class::MOP::Attribute->new('reader' => (
+ reader => 'reader',
+ predicate => 'has_reader',
+ ))
+);
+
+Class::MOP::Attribute->meta->add_attribute(
+ Class::MOP::Attribute->new('writer' => (
+ reader => 'writer',
+ predicate => 'has_writer',
+ ))
+);
+
+Class::MOP::Attribute->meta->add_attribute(
+ Class::MOP::Attribute->new('predicate' => (
+ reader => 'predicate',
+ predicate => 'has_predicate',
+ ))
+);
+
+Class::MOP::Attribute->meta->add_attribute(
+ Class::MOP::Attribute->new('init_arg' => (
+ reader => 'init_arg',
+ predicate => 'has_init_arg',
+ ))
+);
+
+Class::MOP::Attribute->meta->add_attribute(
+ Class::MOP::Attribute->new('default' => (
+ # default has a custom 'reader' method ...
+ predicate => 'has_default',
+ ))
+);
+
+
+# NOTE: (meta-circularity)
+# This should be one of the last things done
+# it will "tie the knot" with Class::MOP::Attribute
+# so that it uses the attributes meta-objects
+# to construct itself.
+Class::MOP::Attribute->meta->add_method('new' => sub {
+ my $class = shift;
+ my $name = shift;
+ my %options = @_;
+
+ (defined $name && $name)
+ || confess "You must provide a name for the attribute";
+ $options{init_arg} = $name
+ if not exists $options{init_arg};
+
+ # return the new object
+ $class->meta->new_object(name => $name, %options);
+});
+
+Class::MOP::Attribute->meta->add_method('clone' => sub {
+ my $self = shift;
+ $self->meta->clone_object($self, @_);
+});
+
+## Try and close Class::MOP::*
+
+Class::MOP::Package ->meta->make_immutable(inline_constructor => 0);
+Class::MOP::Module ->meta->make_immutable(inline_constructor => 0);
+Class::MOP::Class ->meta->make_immutable(inline_constructor => 0);
+Class::MOP::Attribute->meta->make_immutable(inline_constructor => 0);
+Class::MOP::Method ->meta->make_immutable(inline_constructor => 0);
+Class::MOP::Instance ->meta->make_immutable(inline_constructor => 0);
-our $VERSION = '0.01';
-
-# my %METAS;
-# sub UNIVERSAL::meta {
-# my $class = blessed($_[0]) || $_[0];
-# $METAS{$class} ||= Class::MOP::Class->initialize($class)
-# }
1;
=head1 SYNOPSIS
- # ... coming soon
+ # ... This will come later, for now see
+ # the other SYNOPSIS for more information
=head1 DESCRIPTON
made for these tools to keep to the spirit of the Perl 5 object
system that we all know and love.
+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.
+
=head2 What is a Meta Object Protocol?
A meta object protocol is an API to an object system.
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.
+
=head2 Who is this module for?
This module is specifically for anyone who has ever created or
=head2 What changes do I have to make to use this module?
-This module was designed to be as unintrusive as possible. So many of
-it's features are accessible without B<any> change to your existsing
+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.
+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 feature which requires additions to your code are the
-attribute handling and instance construction 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.
+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?
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, while still trying
-to make sure it is fast as well (although only as a secondary
-concern).
+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
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.
+
=item The Attribute protocol
This provides a consistent represenation for an attribute of a
unified approach as possible, while giving the freedom and
flexibility to subclass for specialization.
+See L<Class::MOP::Attribute> for more details.
+
=item The Method protocol
This provides a means of manipulating and introspecting methods in
approach this topic, so we try to keep it pretty basic, while still
making it possible to extend the system in many ways.
-=back
-
-What follows is a more detailed documentation on each specific sub
-protocol.
-
-=head2 The Class protocol
-
-=head3 Class construction
-
-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.
-
-=over 4
-
-=item B<create ($package_name, ?$package_version,
- superclasses => ?@superclasses,
- methods => ?%methods,
- attributes => ?%attributes)>
-
-This returns the basic Class object, bringing the specified
-C<$package_name> into existence and adding any of the
-C<$package_version>, C<@superclasses>, C<%methods> and C<%attributes>
-to it.
-
-=item B<initialize ($package_name)>
-
-This initializes a Class object for a given a C<$package_name>.
-
-=back
-
-=head3 Instance construction
-
-=over 4
-
-=item B<construct_instance ($canidate, %params)>
-
-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.
+See L<Class::MOP::Method> for more details.
=back
-=head3 Informational
-
-=over 4
-
-=item B<name>
-
-This is a read-only attribute which returns the package name that
-the Class is stored in.
-
-=item B<version>
-
-This is a read-only attribute which returns the C<$VERSION> of the
-package the Class is stored in.
-
-=back
-
-=head3 Inheritance Relationships
-
-=over 4
-
-=item B<superclasses (?@superclasses)>
-
-This is a read-write attribute which represents the superclass
-relationships of this Class. Basically, it can get and set the
-C<@ISA> for you.
-
-=item B<class_precedence_list>
-
-This computes the a list of the Class's ancestors in the same order
-in which method dispatch will be done.
+=head1 SEE ALSO
-=back
+=head2 Books
-=head3 Methods
+There are very few books out on Meta Object Protocols and Metaclasses
+because it is such an esoteric topic. The following books are really
+the only ones I have found. If you know of any more, B<I<please>>
+email me and let me know, I would love to hear about them.
=over 4
-=item B<add_method ($method_name, $method)>
-
-This will take a C<$method_name> and CODE reference to that
-C<$method> and install it into the Class.
-
-B<NOTE> : This does absolutely nothing special to C<$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.
-
-=item B<has_method ($method_name)>
-
-This just provides a simple way to check if the Class implements
-a specific C<$method_name>. It will I<not> however, attempt to check
-if the class inherits the method.
-
-This will correctly handle functions defined outside of the package
-that use a fully qualified name (C<sub Package::name { ... }>).
-
-This will correctly handle functions renamed with B<Sub::Name> and
-installed using the symbol tables. However, if you are naming the
-subroutine outside of the package scope, you must use the fully
-qualified name, including the package name, for C<has_method> to
-correctly identify it.
-
-This will attempt to correctly ignore functions imported from other
-packages using B<Exporter>. It breaks down if the function imported
-is an C<__ANON__> sub (such as with C<use constant>), which very well
-may be a valid method being applied to the class.
-
-In short, this method cannot always be trusted to determine if the
-C<$method_name> is actually a method. However, it will DWIM about
-90% of the time, so it's a small trade off IMO.
-
-=item B<get_method ($method_name)>
-
-This will return a CODE reference of the specified C<$method_name>,
-or return undef if that method does not exist.
-
-=item B<remove_method ($method_name)>
-
-This will attempt to remove a given C<$method_name> from the Class.
-It will return the CODE reference that it has removed, and will
-attempt to use B<Sub::Name> to clear the methods associated name.
-
-=item B<get_method_list>
-
-This will return a list of method names for all I<locally> defined
-methods. It does B<not> provide a list of all applicable methods,
-including any inherited ones. If you want a list of all applicable
-methods, use the C<compute_all_applicable_methods> method.
-
-=item B<compute_all_applicable_methods>
-
-This will return a list of all the methods names this Class will
-support, taking into account inheritance. The list will be a list of
-HASH references, each one containing the following information; method
-name, the name of the class in which the method lives and a CODE
-reference for the actual method.
+=item "The Art of the Meta Object Protocol"
-=item B<find_all_methods_by_name ($method_name)>
+=item "Advances in Object-Oriented Metalevel Architecture and Reflection"
-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.
+=item "Putting MetaClasses to Work"
-The list of methods produced is a distinct list, meaning there are no
-duplicates in it. This is especially useful for things like object
-initialization and destruction where you only want the method called
-once, and in the correct order.
+=item "Smalltalk: The Language"
=back
-=head3 Attributes
-
-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.
+=head2 Papers
=over 4
-=item B<add_attribute ($attribute_name, $attribute_meta_object)>
-
-This stores a C<$attribute_meta_object> in the Class object and
-associates it with the C<$attribute_name>. Unlike methods, attributes
-within the MOP are stored as meta-information only. They will be used
-later to construct instances from (see C<construct_instance> above).
-More details about the attribute meta-objects can be found in the
-L<The Attribute protocol> section of this document.
-
-=item B<has_attribute ($attribute_name)>
+=item Uniform and safe metaclass composition
-Checks to see if this Class has an attribute by the name of
-C<$attribute_name> and returns a boolean.
+An excellent paper by the people who brought us the original Traits paper.
+This paper is on how Traits can be used to do safe metaclass composition,
+and offers an excellent introduction section which delves into the topic of
+metaclass compatibility.
-=item B<get_attribute ($attribute_name)>
+L<http://www.iam.unibe.ch/~scg/Archive/Papers/Duca05ySafeMetaclassTrait.pdf>
-Returns the attribute meta-object associated with C<$attribute_name>,
-if none is found, it will return undef.
+=item Safe Metaclass Programming
-=item B<remove_attribute ($attribute_name)>
+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.
-This will remove the attribute meta-object stored at
-C<$attribute_name>, then return the removed attribute meta-object.
-
-B<NOTE:> Removing an attribute will only affect future instances of
-the class, it will not make any attempt to remove the attribute from
-any existing instances of the class.
-
-=item B<get_attribute_list>
-
-This returns a list of attribute names which are defined in the local
-class. If you want a list of all applicable attributes for a class,
-use the C<compute_all_applicable_attributes> method.
-
-=item B<compute_all_applicable_attributes>
-
-This will traverse the inheritance heirachy and return a list of HASH
-references for all the applicable attributes for this class. The HASH
-references will contain the following information; the attribute name,
-the class which the attribute is associated with and the actual
-attribute meta-object
-
-=item B<create_all_accessors>
-
-This will communicate with all of the classes attributes to create
-and install the appropriate accessors. (see L<The Attribute Protocol>
-below for more details).
+L<http://citeseer.ist.psu.edu/37617.html>
=back
-=head2 The Attribute Protocol
-
-This protocol is almost entirely an invention of this module. This is
-because Perl 5 does not have consistent notion of what is an attribute
-of a class. There are so many ways in which this is done, and very few
-(if any) are discoverable by this module.
-
-So, all that said, this module attempts to inject some order into this
-chaos, by introducing a more consistent approach.
-
-=head3 Creation
+=head2 Prior Art
=over 4
-=item B<new ($name, %accessor_description, $class_initialization_arg, $default_value)>
-
- Class::MOP::Attribute->new('$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
- ));
-
-=back
-
-=head3 Informational
+=item The Perl 6 MetaModel work in the Pugs project
=over 4
-=item B<name>
-
-=item B<accessor>
-
-=item B<reader>
+=item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel>
-=item B<writer>
-
-=item B<init_arg>
-
-=item B<default>
+=item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace>
=back
-=head3 Informational predicates
-
-=over 4
-
-=item B<has_accessor>
-
-Returns true if this attribute uses a get/set accessor, and false
-otherwise
-
-=item B<has_reader>
-
-Returns true if this attribute has a reader, and false otherwise
-
-=item B<has_writer>
-
-Returns true if this attribute has a writer, and false otherwise
-
-=item B<has_init_arg>
-
-Returns true if this attribute has a class intialization argument, and
-false otherwise
-
-=item B<has_default>
-
-Returns true if this attribute has a default value, and false
-otherwise.
-
=back
-=head3 Attribute Accessor generation
+=head1 SIMILAR MODULES
-=over 4
+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.
-=item B<generate_accessors>
+=head1 BUGS
-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.
+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.
-=back
+=head1 CODE COVERAGE
-=head2 The Method Protocol
+I use L<Devel::Cover> to test the code coverage of my tests, below is the
+L<Devel::Cover> report on this module's test suite.
-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.
+ ---------------------------- ------ ------ ------ ------ ------ ------ ------
+ File stmt bran cond sub pod time total
+ ---------------------------- ------ ------ ------ ------ ------ ------ ------
+ Class/MOP.pm 100.0 100.0 100.0 100.0 n/a 19.8 100.0
+ Class/MOP/Attribute.pm 100.0 100.0 91.7 61.2 100.0 14.3 87.9
+ Class/MOP/Class.pm 97.6 91.3 77.3 98.4 100.0 56.4 93.2
+ Class/MOP/Instance.pm 91.1 75.0 33.3 91.7 100.0 6.8 90.7
+ Class/MOP/Method.pm 97.6 60.0 52.9 76.9 100.0 1.6 82.6
+ metaclass.pm 100.0 100.0 83.3 100.0 n/a 1.0 97.7
+ ---------------------------- ------ ------ ------ ------ ------ ------ ------
+ Total 97.5 88.5 75.5 82.8 100.0 100.0 91.2
+ ---------------------------- ------ ------ ------ ------ ------ ------ ------
-=head1 SEE ALSO
+=head1 ACKNOWLEDGEMENTS
=over 4
-=item "The Art of the Meta Object Protocol"
+=item Rob Kinyon E<lt>rob@iinteractive.comE<gt>
-=item "Advances in Object-Oriented Metalevel Architecture and Reflection"
+Thanks to Rob for actually getting the development of this module kick-started.
=back
-=head1 AUTHOR
+=head1 AUTHORS
+
+Stevan Little E<lt>stevan@iinteractive.comE<gt>
-Stevan Little E<gt>stevan@iinteractive.comE<lt>
+Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
=head1 COPYRIGHT AND LICENSE
projects / gitmo/Class-MOP.git / blobdiff