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;
-our $VERSION = '0.06';
-
-sub import {
- shift;
- return unless @_;
- if ($_[0] eq ':universal') {
- *UNIVERSAL::meta = sub {
- Class::MOP::Class->initialize(blessed($_[0]) || $_[0])
- };
- }
- else {
- my $pkg = caller();
- no strict 'refs';
- *{$pkg . '::' . $_[0]} = sub {
- Class::MOP::Class->initialize(blessed($_[0]) || $_[0])
- };
- }
-}
+our $VERSION = '0.30';
+
+## ----------------------------------------------------------------------------
+## Setting up our environment ...
+## ----------------------------------------------------------------------------
+## Class::MOP needs to have a few things in the global perl environment so
+## that it can operate effectively. Those things are done here.
+## ----------------------------------------------------------------------------
+
+# ... nothing yet actually ;)
## ----------------------------------------------------------------------------
## Bootstrapping
))
);
+Class::MOP::Class->meta->add_attribute(
+ Class::MOP::Attribute->new('$:instance_metaclass' => (
+ reader => 'instance_metaclass',
+ init_arg => ':instance_metaclass',
+ default => 'Class::MOP::Instance',
+ ))
+);
+
## Class::MOP::Attribute
Class::MOP::Attribute->meta->add_attribute(
Class::MOP::Attribute->meta->add_method('clone' => sub {
my $self = shift;
- my $class = $self->associated_class;
- $self->detach_from_class() if defined $class;
- my $clone = $self->meta->clone_object($self, @_);
- if (defined $class) {
- $self->attach_to_class($class);
- $clone->attach_to_class($class);
- }
- return $clone;
+ $self->meta->clone_object($self, @_);
});
1;
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 3 main sub-protocols:
=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://www.iam.unibe.ch/~scg/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
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 is very
-different from this module.
-
-To start with, it provides wrappers around common Perl data types, and even
-extends those types with more specific subtypes. This module does not
-go into that area at all.
-
-L<Class::Meta> also seems to create it's own custom meta-object protocol,
-which is both more restrictive and more featureful than the vanilla
-Perl 5 one. This module attempts to model the existing Perl 5 MOP as it is.
-
-It's introspection capabilities also seem to be heavily rooted in this
-custom MOP, so that you can only introspect classes which are already
-created with L<Class::Meta>. This module does not make such restictions.
-
-Now, all this said, L<Class::Meta> is much more featureful than B<Class::MOP>
-would ever try to be. But B<Class::MOP> has some features which L<Class::Meta>
-could not easily implement. It would be very possible to completely re-implement
-L<Class::Meta> using B<Class::MOP> and bring some of these features to
-L<Class::Meta> though.
-
-But in the end, this module's admitedly ambitious goals have no direct equal
-on CPAN since surely no one has been crazy enough to try something as silly
-as this ;) until now.
+like this module is L<Class::Meta>, although it's philosophy and the MOP it
+creates are very different from this modules.
=head1 BUGS
exception. If you find a bug please either email me, or add the bug
to cpan-RT.
+=head1 CODE COVERAGE
+
+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.
+
+ ---------------------------- ------ ------ ------ ------ ------ ------ ------
+ File stmt bran cond sub pod time total
+ ---------------------------- ------ ------ ------ ------ ------ ------ ------
+ Class/MOP.pm 100.0 100.0 100.0 100.0 n/a 9.6 100.0
+ Class/MOP/Attribute.pm 100.0 100.0 91.7 73.8 100.0 28.4 92.1
+ Class/MOP/Class.pm 100.0 93.5 82.3 98.2 100.0 56.6 95.7
+ Class/MOP/Method.pm 100.0 64.3 52.9 80.0 100.0 3.5 85.3
+ metaclass.pm 100.0 100.0 80.0 100.0 n/a 1.9 97.4
+ ---------------------------- ------ ------ ------ ------ ------ ------ ------
+ Total 100.0 90.8 79.7 86.2 100.0 100.0 93.6
+ ---------------------------- ------ ------ ------ ------ ------ ------ ------
+
=head1 ACKNOWLEDGEMENTS
=over 4
projects / gitmo/Class-MOP.git / blobdiff