[gitmo/Class-MOP.git] / lib / Class / MOP.pm


package Class::MOP;

use strict;
use warnings;

use Scalar::Util 'blessed';
use Carp         'confess';

use Class::MOP::Class;
use Class::MOP::Attribute;
use Class::MOP::Method;

our $VERSION = '0.01';

sub import {
    shift;
    return unless @_;
    if ($_[0] eq ':universal') {
        *UNIVERSAL::meta = sub { 
            Class::MOP::Class->initialize(blessed($_[0]) || $_[0]) 
        };
    }
}

## ----------------------------------------------------------------------------
## 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::Class

Class::MOP::Class->meta->add_attribute(
    Class::MOP::Attribute->new('$:pkg' => (
        init_arg => ':pkg'
    ))
);

Class::MOP::Class->meta->add_attribute(
    Class::MOP::Attribute->new('%:attrs' => (
        init_arg => ':attrs',
        default  => sub { {} }
    ))
);

## Class::MOP::Attribute

Class::MOP::Attribute->meta->add_attribute(Class::MOP::Attribute->new('name'));
Class::MOP::Attribute->meta->add_attribute(Class::MOP::Attribute->new('accessor'));
Class::MOP::Attribute->meta->add_attribute(Class::MOP::Attribute->new('reader'));
Class::MOP::Attribute->meta->add_attribute(Class::MOP::Attribute->new('writer'));
Class::MOP::Attribute->meta->add_attribute(Class::MOP::Attribute->new('predicate'));
Class::MOP::Attribute->meta->add_attribute(Class::MOP::Attribute->new('init_arg'));
Class::MOP::Attribute->meta->add_attribute(Class::MOP::Attribute->new('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";
    (!exists $options{reader} && !exists $options{writer})
        || confess "You cannot declare an accessor and reader and/or writer functions"
            if exists $options{accessor};
            
    bless $class->meta->construct_instance(name => $name, %options) => $class;
});

# NOTE: (meta-circularity)
# This is how we "tie the knot" for the class
# meta-objects. This is used to construct the
# Class::MOP::Class instances after all the 
# bootstrapping is complete.
Class::MOP::Class->meta->add_method('construct_class_instance' => sub {
    my ($class, $package_name) = @_;
    (defined $package_name && $package_name)
        || confess "You must pass a package name";      
    bless Class::MOP::Class->meta->construct_instance(':pkg' => $package_name) => blessed($class) || $class        
});

1;

__END__

=pod

=head1 NAME 

Class::MOP - A Meta Object Protocol for Perl 5

=head1 SYNOPSIS

  # ... 

=head1 DESCRIPTON

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.

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.

=head2 What is a Meta Object Protocol?

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. 

=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 
it's 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 does 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 optional features as well. 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.

=head1 PROTOCOLS

The protocol is divided into 3 main sub-protocols:

=over 4

=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.

=item The Attribute protocol

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.

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.

=back

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 SEE ALSO

=head2 Books

=over 4

=item "The Art of the Meta Object Protocol"

=item "Advances in Object-Oriented Metalevel Architecture and Reflection"

=item "Putting MetaClasses to Work"

=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/perl5/Perl6-MetaModel>

=item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace>

=back

=back

=head1 AUTHOR

Stevan Little E<gt>stevan@iinteractive.comE<lt>

Rob Kinyon E<gt>rob@iinteractive.comE<lt>

=head1 COPYRIGHT AND LICENSE

Copyright 2006 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. 

=cut
Commit	Line	Data
94b19069	1
	2	package Class::MOP;
	3
	4	use strict;
	5	use warnings;
	6
8b978dd5	7	use Scalar::Util 'blessed';
727919c5	8	use Carp 'confess';
8b978dd5	9
2eb717d5	10	use Class::MOP::Class;
	11	use Class::MOP::Attribute;
	12	use Class::MOP::Method;
	13
94b19069	14	our $VERSION = '0.01';
94b19069	15
2eb717d5	16	sub import {
	17	shift;
	18	return unless @_;
	19	if ($_[0] eq ':universal') {
	20	*UNIVERSAL::meta = sub {
	21	Class::MOP::Class->initialize(blessed($_[0]) \|\| $_[0])
	22	};
	23	}
	24	}
8b978dd5	25
b51af7f9	26	## ----------------------------------------------------------------------------
	27	## Bootstrapping
	28	## ----------------------------------------------------------------------------
	29	## The code below here is to bootstrap our MOP with itself. This is also
	30	## sometimes called "tying the knot". By doing this, we make it much easier
	31	## to extend the MOP through subclassing and such since now you can use the
	32	## MOP itself to extend itself.
	33	##
	34	## Yes, I know, thats weird and insane, but it's a good thing, trust me :)
	35	## ----------------------------------------------------------------------------
727919c5	36
	37	# We need to add in the meta-attributes here so that
	38	# any subclass of Class::MOP::* will be able to
	39	# inherit them using &construct_instance
	40
	41	## Class::MOP::Class
	42
	43	Class::MOP::Class->meta->add_attribute(
	44	Class::MOP::Attribute->new('$:pkg' => (
	45	init_arg => ':pkg'
	46	))
	47	);
	48
	49	Class::MOP::Class->meta->add_attribute(
	50	Class::MOP::Attribute->new('%:attrs' => (
	51	init_arg => ':attrs',
	52	default => sub { {} }
	53	))
	54	);
	55
	56	## Class::MOP::Attribute
	57
	58	Class::MOP::Attribute->meta->add_attribute(Class::MOP::Attribute->new('name'));
	59	Class::MOP::Attribute->meta->add_attribute(Class::MOP::Attribute->new('accessor'));
	60	Class::MOP::Attribute->meta->add_attribute(Class::MOP::Attribute->new('reader'));
	61	Class::MOP::Attribute->meta->add_attribute(Class::MOP::Attribute->new('writer'));
	62	Class::MOP::Attribute->meta->add_attribute(Class::MOP::Attribute->new('predicate'));
	63	Class::MOP::Attribute->meta->add_attribute(Class::MOP::Attribute->new('init_arg'));
	64	Class::MOP::Attribute->meta->add_attribute(Class::MOP::Attribute->new('default'));
	65
	66	# NOTE: (meta-circularity)
	67	# This should be one of the last things done
	68	# it will "tie the knot" with Class::MOP::Attribute
	69	# so that it uses the attributes meta-objects
	70	# to construct itself.
	71	Class::MOP::Attribute->meta->add_method('new' => sub {
	72	my $class = shift;
	73	my $name = shift;
	74	my %options = @_;
	75
	76	(defined $name && $name)
	77	\|\| confess "You must provide a name for the attribute";
	78	(!exists $options{reader} && !exists $options{writer})
	79	\|\| confess "You cannot declare an accessor and reader and/or writer functions"
	80	if exists $options{accessor};
	81
	82	bless $class->meta->construct_instance(name => $name, %options) => $class;
	83	});
	84
	85	# NOTE: (meta-circularity)
	86	# This is how we "tie the knot" for the class
	87	# meta-objects. This is used to construct the
	88	# Class::MOP::Class instances after all the
	89	# bootstrapping is complete.
	90	Class::MOP::Class->meta->add_method('construct_class_instance' => sub {
	91	my ($class, $package_name) = @_;
	92	(defined $package_name && $package_name)
	93	\|\| confess "You must pass a package name";
	94	bless Class::MOP::Class->meta->construct_instance(':pkg' => $package_name) => blessed($class) \|\| $class
	95	});
	96
94b19069	97	1;
	98
	99	__END__
	100
	101	=pod
	102
	103	=head1 NAME
	104
	105	Class::MOP - A Meta Object Protocol for Perl 5
	106
	107	=head1 SYNOPSIS
	108
fe122940	109	# ...
94b19069	110
	111	=head1 DESCRIPTON
	112
	113	This module is an attempt to create a meta object protocol for the
	114	Perl 5 object system. It makes no attempt to change the behavior or
	115	characteristics of the Perl 5 object system, only to create a
27e31eaf	116	protocol for its manipulation and introspection.
94b19069	117
	118	That said, it does attempt to create the tools for building a rich
	119	set of extensions to the Perl 5 object system. Every attempt has been
	120	made for these tools to keep to the spirit of the Perl 5 object
	121	system that we all know and love.
	122
bfe4d0fc	123	=head2 What is a Meta Object Protocol?
	124
	125	A meta object protocol is an API to an object system.
	126
	127	To be more specific, it is a set of abstractions of the components of
	128	an object system (typically things like; classes, object, methods,
	129	object attributes, etc.). These abstractions can then be used to both
	130	inspect and manipulate the object system which they describe.
	131
	132	It can be said that there are two MOPs for any object system; the
	133	implicit MOP, and the explicit MOP. The implicit MOP handles things
	134	like method dispatch or inheritance, which happen automatically as
	135	part of how the object system works. The explicit MOP typically
	136	handles the introspection/reflection features of the object system.
	137	All object systems have implicit MOPs, without one, they would not
	138	work. Explict MOPs however as less common, and depending on the
	139	language can vary from restrictive (Reflection in Java or C#) to
	140	wide open (CLOS is a perfect example).
	141
e16da3e6	142	=head2 Yet Another Class Builder!! Why?
	143
	144	This is B<not> a class builder so much as it is a I<class builder
	145	B<builder>>. My intent is that an end user does not use this module
	146	directly, but instead this module is used by module authors to
	147	build extensions and features onto the Perl 5 object system.
	148
94b19069	149	=head2 Who is this module for?
	150
	151	This module is specifically for anyone who has ever created or
	152	wanted to create a module for the Class:: namespace. The tools which
	153	this module will provide will hopefully make it easier to do more
	154	complex things with Perl 5 classes by removing such barriers as
	155	the need to hack the symbol tables, or understand the fine details
	156	of method dispatch.
	157
bfe4d0fc	158	=head2 What changes do I have to make to use this module?
bfe4d0fc	159
2eb717d5	160	This module was designed to be as unintrusive as possible. Many of
bfe4d0fc	161	it's features are accessible without B<any> change to your existsing
bfe4d0fc	162	code at all. It is meant to be a compliment to your existing code and
2eb717d5	163	not an intrusion on your code base. Unlike many other B<Class::>
	164	modules, this module does require you subclass it, or even that you
	165	C<use> it in within your module's package.
bfe4d0fc	166
2eb717d5	167	The only features which requires additions to your code are the
	168	attribute handling and instance construction features, and these are
	169	both optional features as well. The only reason for this is because
	170	Perl 5's object system does not actually have these features built
	171	in. More information about this feature can be found below.
bfe4d0fc	172
	173	=head2 A Note about Performance?
	174
	175	It is a common misconception that explict MOPs are performance drains.
	176	But this is not a universal truth at all, it is an side-effect of
	177	specific implementations. For instance, using Java reflection is much
	178	slower because the JVM cannot take advantage of any compiler
	179	optimizations, and the JVM has to deal with much more runtime type
	180	information as well. Reflection in C# is marginally better as it was
	181	designed into the language and runtime (the CLR). In contrast, CLOS
	182	(the Common Lisp Object System) was built to support an explicit MOP,
	183	and so performance is tuned for it.
	184
	185	This library in particular does it's absolute best to avoid putting
2eb717d5	186	B<any> drain at all upon your code's performance. In fact, by itself
	187	it does nothing to affect your existing code. So you only pay for
	188	what you actually use.
bfe4d0fc	189
94b19069	190	=head1 PROTOCOLS
	191
	192	The protocol is divided into 3 main sub-protocols:
	193
	194	=over 4
	195
	196	=item The Class protocol
	197
	198	This provides a means of manipulating and introspecting a Perl 5
	199	class. It handles all of symbol table hacking for you, and provides
	200	a rich set of methods that go beyond simple package introspection.
	201
552e3d24	202	See L<Class::MOP::Class> for more details.
552e3d24	203
94b19069	204	=item The Attribute protocol
	205
	206	This provides a consistent represenation for an attribute of a
	207	Perl 5 class. Since there are so many ways to create and handle
	208	atttributes in Perl 5 OO, this attempts to provide as much of a
	209	unified approach as possible, while giving the freedom and
	210	flexibility to subclass for specialization.
	211
552e3d24	212	See L<Class::MOP::Attribute> for more details.
552e3d24	213
94b19069	214	=item The Method protocol
	215
	216	This provides a means of manipulating and introspecting methods in
	217	the Perl 5 object system. As with attributes, there are many ways to
	218	approach this topic, so we try to keep it pretty basic, while still
	219	making it possible to extend the system in many ways.
	220
552e3d24	221	See L<Class::MOP::Method> for more details.
94b19069	222
	223	=back
	224
7184ca14	225	head1 BUGS
	226
	227	All complex software has bugs lurking in it, and this module is no
	228	exception. If you find a bug please either email me, or add the bug
	229	to cpan-RT.
	230
552e3d24	231	=head1 SEE ALSO
8b978dd5	232
552e3d24	233	=head2 Books
8b978dd5	234
	235	=over 4
	236
552e3d24	237	=item "The Art of the Meta Object Protocol"
8b978dd5	238
552e3d24	239	=item "Advances in Object-Oriented Metalevel Architecture and Reflection"
8b978dd5	240
b51af7f9	241	=item "Putting MetaClasses to Work"
b51af7f9	242
94b19069	243	=back
94b19069	244
552e3d24	245	=head2 Prior Art
8b978dd5	246
	247	=over 4
	248
7184ca14	249	=item The Perl 6 MetaModel work in the Pugs project
8b978dd5	250
	251	=over 4
	252
552e3d24	253	=item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel>
8b978dd5	254
552e3d24	255	=item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace>
8b978dd5	256
	257	=back
	258
94b19069	259	=back
	260
	261	=head1 AUTHOR
	262
	263	Stevan Little E<gt>stevan@iinteractive.comE<lt>
	264
552e3d24	265	Rob Kinyon E<gt>rob@iinteractive.comE<lt>
552e3d24	266
94b19069	267	=head1 COPYRIGHT AND LICENSE
	268
	269	Copyright 2006 by Infinity Interactive, Inc.
	270
	271	L<http://www.iinteractive.com>
	272
	273	This library is free software; you can redistribute it and/or modify
	274	it under the same terms as Perl itself.
	275
	276	=cut