Moose::Cookbook::Meta:UseMoose::Cookbook::Meta::GlobRefoInstanceMetaclass(3pm)
NAME
Moose::Cookbook::Meta::GlobRef_InstanceMetaclass - Creating a glob
reference meta-instance class
VERSION
version 2.2203
SYNOPSIS
package My::Meta::Instance;
use Scalar::Util qw( weaken );
use Symbol qw( gensym );
use Moose::Role;
sub create_instance {
my $self = shift;
my $sym = gensym();
bless $sym, $self->_class_name;
}
sub clone_instance {
my ( $self, $instance ) = @_;
my $new_sym = gensym();
%{*$new_sym} = %{*$instance};
bless $new_sym, $self->_class_name;
}
sub get_slot_value {
my ( $self, $instance, $slot_name ) = @_;
return *$instance->{$slot_name};
}
sub set_slot_value {
my ( $self, $instance, $slot_name, $value ) = @_;
*$instance->{$slot_name} = $value;
}
sub deinitialize_slot {
my ( $self, $instance, $slot_name ) = @_;
delete *$instance->{$slot_name};
}
sub is_slot_initialized {
my ( $self, $instance, $slot_name ) = @_;
exists *$instance->{$slot_name};
}
sub weaken_slot_value {
my ( $self, $instance, $slot_name ) = @_;
weaken *$instance->{$slot_name};
}
sub inline_create_instance {
my ( $self, $class_variable ) = @_;
return 'do { my $sym = Symbol::gensym(); bless $sym, ' . $class_variable . ' }';
}
sub inline_slot_access {
my ( $self, $instance, $slot_name ) = @_;
return '*{' . $instance . '}->{' . $slot_name . '}';
}
package MyApp::User;
use Moose;
Moose::Util::MetaRole::apply_metaroles(
for => __PACKAGE__,
class_metaroles => {
instance => ['My::Meta::Instance'],
},
);
has 'name' => (
is => 'rw',
isa => 'Str',
);
has 'email' => (
is => 'rw',
isa => 'Str',
);
DESCRIPTION
This recipe shows how to build your own meta-instance. The meta
instance is the metaclass that creates object instances and helps
manages access to attribute slots.
In this example, we're creating a meta-instance that is based on a glob
reference rather than a hash reference. This example is largely based
on the Piotr Roszatycki's MooseX::GlobRef module.
Our extension is a role which will be applied to Moose::Meta::Instance,
which creates hash reference based objects. We need to override all the
methods which make assumptions about the object's data structure.
The first method we override is "create_instance":
sub create_instance {
my $self = shift;
my $sym = gensym();
bless $sym, $self->_class_name;
}
This returns an glob reference which has been blessed into our meta-
instance's associated class.
We also override "clone_instance" to create a new array reference:
sub clone_instance {
my ( $self, $instance ) = @_;
my $new_sym = gensym();
%{*$new_sym} = %{*$instance};
bless $new_sym, $self->_class_name;
}
After that, we have a series of methods which mediate access to the
object's slots (attributes are stored in "slots"). In the default
instance class, these expect the object to be a hash reference, but we
need to change this to expect a glob reference instead.
sub get_slot_value {
my ( $self, $instance, $slot_name ) = @_;
*$instance->{$slot_name};
}
This level of indirection probably makes our instance class slower than
the default. However, when attribute access is inlined, this lookup
will be cached:
sub inline_slot_access {
my ( $self, $instance, $slot_name ) = @_;
return '*{' . $instance . '}->{' . $slot_name . '}';
}
The code snippet that the "inline_slot_access" method returns will get
"eval"'d once per attribute.
Finally, we use this meta-instance in our "MyApp::User" class:
Moose::Util::MetaRole::apply_metaroles(
for => __PACKAGE__,
class_metaroles => {
instance => ['My::Meta::Instance'],
},
);
We actually don't recommend the use of Moose::Util::MetaRole directly
in your class in most cases. Typically, this would be provided by a
Moose::Exporter-based module which handles applying the role for you.
CONCLUSION
This recipe shows how to create your own meta-instance class. It's
unlikely that you'll need to do this yourself, but it's interesting to
take a peek at how Moose works under the hood.
SEE ALSO
There are a few meta-instance class extensions on CPAN:
• MooseX::Singleton
This module extends the instance class in order to ensure that the
object is a singleton. The instance it uses is still a blessed hash
reference.
• MooseX::GlobRef
This module makes the instance a blessed glob reference. This lets
you use a handle as an object instance.
AUTHORS
• Stevan Little <stevan@cpan.org>
• Dave Rolsky <autarch@urth.org>
• Jesse Luehrs <doy@cpan.org>
• Shawn M Moore <sartak@cpan.org>
• יובל קוג'מן (Yuval Kogman) <nothingmuch@woobling.org>
• Karen Etheridge <ether@cpan.org>
• Florian Ragwitz <rafl@debian.org>
• Hans Dieter Pearcey <hdp@cpan.org>
• Chris Prather <chris@prather.org>
• Matt S Trout <mstrout@cpan.org>
COPYRIGHT AND LICENSE
This software is copyright (c) 2006 by Infinity Interactive, Inc.
This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.
perl v5.36.0 Moose::Cookbook::Meta::GlobRef_InstanceMetaclass(3pm)
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