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package # hide the package from PAUSE
InsideOutClass::Attribute;
use strict;
use warnings;
our $VERSION = '0.02';
use Carp 'confess';
use Scalar::Util 'refaddr';
use base 'Class::MOP::Attribute';
sub initialize_instance_slot {
my ($self, $meta_instance, $instance, $params) = @_;
my $init_arg = $self->init_arg;
# try to fetch the init arg from the %params ...
my $val;
$val = $params->{$init_arg} if exists $params->{$init_arg};
# if nothing was in the %params, we can use the
# attribute's default value (if it has one)
if (!defined $val && defined $self->default) {
$val = $self->default($instance);
}
my $_meta_instance = $self->associated_class->get_meta_instance;
$_meta_instance->initialize_slot($instance, $self->name);
$_meta_instance->set_slot_value($instance, $self->name, $val);
}
sub accessor_metaclass { 'InsideOutClass::Method::Accessor' }
package # hide the package from PAUSE
InsideOutClass::Method::Accessor;
use strict;
use warnings;
our $VERSION = '0.01';
use Carp 'confess';
use Scalar::Util 'refaddr';
use base 'Class::MOP::Method::Accessor';
## Method generation helpers
sub _generate_accessor_method {
my $attr = (shift)->associated_attribute;
my $meta_class = $attr->associated_class;
my $attr_name = $attr->name;
return sub {
my $meta_instance = $meta_class->get_meta_instance;
$meta_instance->set_slot_value($_[0], $attr_name, $_[1]) if scalar(@_) == 2;
$meta_instance->get_slot_value($_[0], $attr_name);
};
}
sub _generate_reader_method {
my $attr = (shift)->associated_attribute;
my $meta_class = $attr->associated_class;
my $attr_name = $attr->name;
return sub {
confess "Cannot assign a value to a read-only accessor" if @_ > 1;
$meta_class->get_meta_instance
->get_slot_value($_[0], $attr_name);
};
}
sub _generate_writer_method {
my $attr = (shift)->associated_attribute;
my $meta_class = $attr->associated_class;
my $attr_name = $attr->name;
return sub {
$meta_class->get_meta_instance
->set_slot_value($_[0], $attr_name, $_[1]);
};
}
sub _generate_predicate_method {
my $attr = (shift)->associated_attribute;
my $meta_class = $attr->associated_class;
my $attr_name = $attr->name;
return sub {
defined $meta_class->get_meta_instance
->get_slot_value($_[0], $attr_name) ? 1 : 0;
};
}
package # hide the package from PAUSE
InsideOutClass::Instance;
use strict;
use warnings;
our $VERSION = '0.01';
use Carp 'confess';
use Scalar::Util 'refaddr';
use base 'Class::MOP::Instance';
sub create_instance {
my ($self, $class) = @_;
bless \(my $instance), $self->_class_name;
}
sub get_slot_value {
my ($self, $instance, $slot_name) = @_;
$self->associated_metaclass->get_package_symbol('%' . $slot_name)->{refaddr $instance};
}
sub set_slot_value {
my ($self, $instance, $slot_name, $value) = @_;
$self->associated_metaclass->get_package_symbol('%' . $slot_name)->{refaddr $instance} = $value;
}
sub initialize_slot {
my ($self, $instance, $slot_name) = @_;
$self->associated_metaclass->add_package_symbol(('%' . $slot_name) => {})
unless $self->associated_metaclass->has_package_symbol('%' . $slot_name);
$self->associated_metaclass->get_package_symbol('%' . $slot_name)->{refaddr $instance} = undef;
}
sub is_slot_initialized {
my ($self, $instance, $slot_name) = @_;
return 0 unless $self->associated_metaclass->has_package_symbol('%' . $slot_name);
return exists $self->associated_metaclass->get_package_symbol('%' . $slot_name)->{refaddr $instance} ? 1 : 0;
}
1;
__END__
=pod
=head1 NAME
InsideOutClass - A set of example metaclasses which implement the Inside-Out technique
=head1 SYNOPSIS
package Foo;
use metaclass (
':attribute_metaclass' => 'InsideOutClass::Attribute',
':instance_metaclass' => 'InsideOutClass::Instance'
);
__PACKAGE__->meta->add_attribute('foo' => (
reader => 'get_foo',
writer => 'set_foo'
));
sub new {
my $class = shift;
$class->meta->new_object(@_);
}
# now you can just use the class as normal
=head1 DESCRIPTION
This is a set of example metaclasses which implement the Inside-Out
class technique. What follows is a brief explaination of the code
found in this module.
We must create a subclass of B<Class::MOP::Instance> and override
the slot operations. This requires
overloading C<get_slot_value>, C<set_slot_value>, C<slot_initialized>, and
C<initialize_slot>, as well as their inline counterparts. Additionally we
overload C<add_slot> in order to initialize the global hash containing the
actual slot values.
And that is pretty much all. Of course I am ignoring need for
inside-out objects to be C<DESTROY>-ed, and some other details as
well (threading, etc), but this is an example. A real implementation is left as
an exercise to the reader.
=head1 AUTHORS
Stevan Little E<lt>stevan@iinteractive.comE<gt>
Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
=head1 COPYRIGHT AND LICENSE
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.
=cut
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