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package # hide the package from PAUSE
ClassEncapsulatedAttributes;
use strict;
use warnings;
our $VERSION = '0.06';
use parent 'Class::MOP::Class';
sub initialize {
(shift)->SUPER::initialize(@_,
# use the custom attribute metaclass here
'attribute_metaclass' => 'ClassEncapsulatedAttributes::Attribute',
);
}
sub construct_instance {
my ($class, %params) = @_;
my $meta_instance = $class->get_meta_instance;
my $instance = $meta_instance->create_instance();
# initialize *ALL* attributes, including masked ones (as opposed to applicable)
foreach my $current_class ($class->class_precedence_list()) {
my $meta = $current_class->meta;
foreach my $attr_name ($meta->get_attribute_list()) {
my $attr = $meta->get_attribute($attr_name);
$attr->initialize_instance_slot($meta_instance, $instance, \%params);
}
}
return $instance;
}
package # hide the package from PAUSE
ClassEncapsulatedAttributes::Attribute;
use strict;
use warnings;
our $VERSION = '0.04';
use parent 'Class::MOP::Attribute';
# alter the way parameters are specified
sub initialize_instance_slot {
my ($self, $meta_instance, $instance, $params) = @_;
# if the attr has an init_arg, use that, otherwise,
# use the attributes name itself as the init_arg
my $init_arg = $self->init_arg();
# try to fetch the init arg from the %params ...
my $class = $self->associated_class;
my $val;
$val = $params->{$class->name}->{$init_arg}
if exists $params->{$class->name} &&
exists ${$params->{$class->name}}{$init_arg};
# if nothing was in the %params, we can use the
# attribute's default value (if it has one)
if (!defined $val && $self->has_default) {
$val = $self->default($instance);
}
# now add this to the instance structure
$meta_instance->set_slot_value($instance, $self->name, $val);
}
sub name {
my $self = shift;
return ($self->associated_class->name . '::' . $self->SUPER::name)
}
1;
__END__
=pod
=head1 NAME
ClassEncapsulatedAttributes - A set of example metaclasses with class encapsulated attributes
=head1 SYNOPSIS
package Foo;
use metaclass 'ClassEncapsulatedAttributes';
Foo->meta->add_attribute('foo' => (
accessor => 'Foo_foo',
default => 'init in FOO'
));
sub new {
my $class = shift;
$class->meta->new_object(@_);
}
package Bar;
our @ISA = ('Foo');
# duplicate the attribute name here
Bar->meta->add_attribute('foo' => (
accessor => 'Bar_foo',
default => 'init in BAR'
));
# ... later in other code ...
my $bar = Bar->new();
prints $bar->Bar_foo(); # init in BAR
prints $bar->Foo_foo(); # init in FOO
# and ...
my $bar = Bar->new(
'Foo' => { 'foo' => 'Foo::foo' },
'Bar' => { 'foo' => 'Bar::foo' }
);
prints $bar->Bar_foo(); # Foo::foo
prints $bar->Foo_foo(); # Bar::foo
=head1 DESCRIPTION
This is an example metaclass which encapsulates a class's
attributes on a per-class basis. This means that there is no
possibility of name clashes with inherited attributes. This
is similar to how C++ handles its data members.
=head1 ACKNOWLEDGEMENTS
Thanks to Yuval "nothingmuch" Kogman for the idea for this example.
=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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