[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]) 
        };
    }
    else {
        my $pkg = caller();
        no strict 'refs';
        *{$pkg . '::' . $_[0]} = sub { 
            Class::MOP::Class->initialize(blessed($_[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;
});

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	}
1a7ebbb3	24	else {
	25	my $pkg = caller();
	26	no strict 'refs';
	27	*{$pkg . '::' . $_[0]} = sub {
	28	Class::MOP::Class->initialize(blessed($_[0]) \|\| $_[0])
	29	};
	30	}
2eb717d5	31	}
8b978dd5	32
b51af7f9	33	## ----------------------------------------------------------------------------
	34	## Bootstrapping
	35	## ----------------------------------------------------------------------------
	36	## The code below here is to bootstrap our MOP with itself. This is also
	37	## sometimes called "tying the knot". By doing this, we make it much easier
	38	## to extend the MOP through subclassing and such since now you can use the
	39	## MOP itself to extend itself.
	40	##
	41	## Yes, I know, thats weird and insane, but it's a good thing, trust me :)
	42	## ----------------------------------------------------------------------------
727919c5	43
	44	# We need to add in the meta-attributes here so that
	45	# any subclass of Class::MOP::* will be able to
	46	# inherit them using &construct_instance
	47
	48	## Class::MOP::Class
	49
	50	Class::MOP::Class->meta->add_attribute(
	51	Class::MOP::Attribute->new('$:pkg' => (
	52	init_arg => ':pkg'
	53	))
	54	);
	55
	56	Class::MOP::Class->meta->add_attribute(
	57	Class::MOP::Attribute->new('%:attrs' => (
	58	init_arg => ':attrs',
	59	default => sub { {} }
	60	))
	61	);
	62
	63	## Class::MOP::Attribute
	64
	65	Class::MOP::Attribute->meta->add_attribute(Class::MOP::Attribute->new('name'));
	66	Class::MOP::Attribute->meta->add_attribute(Class::MOP::Attribute->new('accessor'));
	67	Class::MOP::Attribute->meta->add_attribute(Class::MOP::Attribute->new('reader'));
	68	Class::MOP::Attribute->meta->add_attribute(Class::MOP::Attribute->new('writer'));
	69	Class::MOP::Attribute->meta->add_attribute(Class::MOP::Attribute->new('predicate'));
	70	Class::MOP::Attribute->meta->add_attribute(Class::MOP::Attribute->new('init_arg'));
	71	Class::MOP::Attribute->meta->add_attribute(Class::MOP::Attribute->new('default'));
	72
	73	# NOTE: (meta-circularity)
	74	# This should be one of the last things done
	75	# it will "tie the knot" with Class::MOP::Attribute
	76	# so that it uses the attributes meta-objects
	77	# to construct itself.
	78	Class::MOP::Attribute->meta->add_method('new' => sub {
	79	my $class = shift;
	80	my $name = shift;
	81	my %options = @_;
	82
	83	(defined $name && $name)
	84	\|\| confess "You must provide a name for the attribute";
	85	(!exists $options{reader} && !exists $options{writer})
	86	\|\| confess "You cannot declare an accessor and reader and/or writer functions"
	87	if exists $options{accessor};
	88
	89	bless $class->meta->construct_instance(name => $name, %options) => $class;
	90	});
	91
94b19069	92	1;
	93
	94	__END__
	95
	96	=pod
	97
	98	=head1 NAME
	99
	100	Class::MOP - A Meta Object Protocol for Perl 5
	101
	102	=head1 SYNOPSIS
	103
fe122940	104	# ...
94b19069	105
	106	=head1 DESCRIPTON
	107
	108	This module is an attempt to create a meta object protocol for the
	109	Perl 5 object system. It makes no attempt to change the behavior or
	110	characteristics of the Perl 5 object system, only to create a
27e31eaf	111	protocol for its manipulation and introspection.
94b19069	112
	113	That said, it does attempt to create the tools for building a rich
	114	set of extensions to the Perl 5 object system. Every attempt has been
	115	made for these tools to keep to the spirit of the Perl 5 object
	116	system that we all know and love.
	117
bfe4d0fc	118	=head2 What is a Meta Object Protocol?
	119
	120	A meta object protocol is an API to an object system.
	121
	122	To be more specific, it is a set of abstractions of the components of
	123	an object system (typically things like; classes, object, methods,
	124	object attributes, etc.). These abstractions can then be used to both
	125	inspect and manipulate the object system which they describe.
	126
	127	It can be said that there are two MOPs for any object system; the
	128	implicit MOP, and the explicit MOP. The implicit MOP handles things
	129	like method dispatch or inheritance, which happen automatically as
	130	part of how the object system works. The explicit MOP typically
	131	handles the introspection/reflection features of the object system.
	132	All object systems have implicit MOPs, without one, they would not
	133	work. Explict MOPs however as less common, and depending on the
	134	language can vary from restrictive (Reflection in Java or C#) to
	135	wide open (CLOS is a perfect example).
	136
e16da3e6	137	=head2 Yet Another Class Builder!! Why?
	138
	139	This is B<not> a class builder so much as it is a I<class builder
	140	B<builder>>. My intent is that an end user does not use this module
	141	directly, but instead this module is used by module authors to
	142	build extensions and features onto the Perl 5 object system.
	143
94b19069	144	=head2 Who is this module for?
	145
	146	This module is specifically for anyone who has ever created or
	147	wanted to create a module for the Class:: namespace. The tools which
	148	this module will provide will hopefully make it easier to do more
	149	complex things with Perl 5 classes by removing such barriers as
	150	the need to hack the symbol tables, or understand the fine details
	151	of method dispatch.
	152
bfe4d0fc	153	=head2 What changes do I have to make to use this module?
bfe4d0fc	154
2eb717d5	155	This module was designed to be as unintrusive as possible. Many of
bfe4d0fc	156	it's features are accessible without B<any> change to your existsing
bfe4d0fc	157	code at all. It is meant to be a compliment to your existing code and
2eb717d5	158	not an intrusion on your code base. Unlike many other B<Class::>
	159	modules, this module does require you subclass it, or even that you
	160	C<use> it in within your module's package.
bfe4d0fc	161
2eb717d5	162	The only features which requires additions to your code are the
	163	attribute handling and instance construction features, and these are
	164	both optional features as well. The only reason for this is because
	165	Perl 5's object system does not actually have these features built
	166	in. More information about this feature can be found below.
bfe4d0fc	167
	168	=head2 A Note about Performance?
	169
	170	It is a common misconception that explict MOPs are performance drains.
	171	But this is not a universal truth at all, it is an side-effect of
	172	specific implementations. For instance, using Java reflection is much
	173	slower because the JVM cannot take advantage of any compiler
	174	optimizations, and the JVM has to deal with much more runtime type
	175	information as well. Reflection in C# is marginally better as it was
	176	designed into the language and runtime (the CLR). In contrast, CLOS
	177	(the Common Lisp Object System) was built to support an explicit MOP,
	178	and so performance is tuned for it.
	179
	180	This library in particular does it's absolute best to avoid putting
2eb717d5	181	B<any> drain at all upon your code's performance. In fact, by itself
	182	it does nothing to affect your existing code. So you only pay for
	183	what you actually use.
bfe4d0fc	184
94b19069	185	=head1 PROTOCOLS
	186
	187	The protocol is divided into 3 main sub-protocols:
	188
	189	=over 4
	190
	191	=item The Class protocol
	192
	193	This provides a means of manipulating and introspecting a Perl 5
	194	class. It handles all of symbol table hacking for you, and provides
	195	a rich set of methods that go beyond simple package introspection.
	196
552e3d24	197	See L<Class::MOP::Class> for more details.
552e3d24	198
94b19069	199	=item The Attribute protocol
	200
	201	This provides a consistent represenation for an attribute of a
	202	Perl 5 class. Since there are so many ways to create and handle
	203	atttributes in Perl 5 OO, this attempts to provide as much of a
	204	unified approach as possible, while giving the freedom and
	205	flexibility to subclass for specialization.
	206
552e3d24	207	See L<Class::MOP::Attribute> for more details.
552e3d24	208
94b19069	209	=item The Method protocol
	210
	211	This provides a means of manipulating and introspecting methods in
	212	the Perl 5 object system. As with attributes, there are many ways to
	213	approach this topic, so we try to keep it pretty basic, while still
	214	making it possible to extend the system in many ways.
	215
552e3d24	216	See L<Class::MOP::Method> for more details.
94b19069	217
	218	=back
	219
7184ca14	220	head1 BUGS
	221
	222	All complex software has bugs lurking in it, and this module is no
	223	exception. If you find a bug please either email me, or add the bug
	224	to cpan-RT.
	225
552e3d24	226	=head1 SEE ALSO
8b978dd5	227
552e3d24	228	=head2 Books
8b978dd5	229
	230	=over 4
	231
552e3d24	232	=item "The Art of the Meta Object Protocol"
8b978dd5	233
552e3d24	234	=item "Advances in Object-Oriented Metalevel Architecture and Reflection"
8b978dd5	235
b51af7f9	236	=item "Putting MetaClasses to Work"
b51af7f9	237
94b19069	238	=back
94b19069	239
552e3d24	240	=head2 Prior Art
8b978dd5	241
	242	=over 4
	243
7184ca14	244	=item The Perl 6 MetaModel work in the Pugs project
8b978dd5	245
	246	=over 4
	247
552e3d24	248	=item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel>
8b978dd5	249
552e3d24	250	=item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace>
8b978dd5	251
	252	=back
	253
94b19069	254	=back
	255
	256	=head1 AUTHOR
	257
	258	Stevan Little E<gt>stevan@iinteractive.comE<lt>
	259
552e3d24	260	Rob Kinyon E<gt>rob@iinteractive.comE<lt>
552e3d24	261
94b19069	262	=head1 COPYRIGHT AND LICENSE
	263
	264	Copyright 2006 by Infinity Interactive, Inc.
	265
	266	L<http://www.iinteractive.com>
	267
	268	This library is free software; you can redistribute it and/or modify
	269	it under the same terms as Perl itself.
	270
	271	=cut