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Always turn off hyphenation; it makes .\" way too many mistakes in technical documents. .if n .ad l .nh .SH "NAME" Moose::Cookbook::Meta::GlobRef_InstanceMetaclass \- Creating a glob reference meta\-instance class .SH "VERSION" .IX Header "VERSION" version 2.1213 .SH "SYNOPSIS" .IX Header "SYNOPSIS" .Vb 1 \& 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 \*(Aqdo { my $sym = Symbol::gensym(); bless $sym, \*(Aq . $class_variable . \*(Aq }\*(Aq; \& } \& \& sub inline_slot_access { \& my ( $self, $instance, $slot_name ) = @_; \& return \*(Aq*{\*(Aq . $instance . \*(Aq}\->{\*(Aq . $slot_name . \*(Aq}\*(Aq; \& } \& \& package MyApp::User; \& \& use Moose; \& Moose::Util::MetaRole::apply_metaroles( \& for => _\|_PACKAGE_\|_, \& class_metaroles => { \& instance => [\*(AqMy::Meta::Instance\*(Aq], \& }, \& ); \& \& has \*(Aqname\*(Aq => ( \& is => \*(Aqrw\*(Aq, \& isa => \*(AqStr\*(Aq, \& ); \& \& has \*(Aqemail\*(Aq => ( \& is => \*(Aqrw\*(Aq, \& isa => \*(AqStr\*(Aq, \& ); .Ve .SH "DESCRIPTION" .IX Header "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. .PP 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. .PP 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. .PP The first method we override is \f(CW\*(C`create_instance\*(C'\fR: .PP .Vb 5 \& sub create_instance { \& my $self = shift; \& my $sym = gensym(); \& bless $sym, $self\->_class_name; \& } .Ve .PP This returns an glob reference which has been blessed into our meta-instance's associated class. .PP We also override \f(CW\*(C`clone_instance\*(C'\fR to create a new array reference: .PP .Vb 2 \& sub clone_instance { \& my ( $self, $instance ) = @_; \& \& my $new_sym = gensym(); \& %{*$new_sym} = %{*$instance}; \& \& bless $new_sym, $self\->_class_name; \& } .Ve .PP After that, we have a series of methods which mediate access to the object's slots (attributes are stored in \*(L"slots\*(R"). 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. .PP .Vb 4 \& sub get_slot_value { \& my ( $self, $instance, $slot_name ) = @_; \& *$instance\->{$slot_name}; \& } .Ve .PP This level of indirection probably makes our instance class \fIslower\fR than the default. However, when attribute access is inlined, this lookup will be cached: .PP .Vb 4 \& sub inline_slot_access { \& my ( $self, $instance, $slot_name ) = @_; \& return \*(Aq*{\*(Aq . $instance . \*(Aq}\->{\*(Aq . $slot_name . \*(Aq}\*(Aq; \& } .Ve .PP The code snippet that the \f(CW\*(C`inline_slot_access\*(C'\fR method returns will get \f(CW\*(C`eval\*(C'\fR'd once per attribute. .PP Finally, we use this meta-instance in our \f(CW\*(C`MyApp::User\*(C'\fR class: .PP .Vb 6 \& Moose::Util::MetaRole::apply_metaroles( \& for => _\|_PACKAGE_\|_, \& class_metaroles => { \& instance => [\*(AqMy::Meta::Instance\*(Aq], \& }, \& ); .Ve .PP 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. .SH "CONCLUSION" .IX Header "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. .SH "SEE ALSO" .IX Header "SEE ALSO" There are a few meta-instance class extensions on \s-1CPAN:\s0 .IP "\(bu" 4 MooseX::Singleton .Sp 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. .IP "\(bu" 4 MooseX::GlobRef .Sp This module makes the instance a blessed glob reference. This lets you use a handle as an object instance. .SH "AUTHORS" .IX Header "AUTHORS" .IP "\(bu" 4 Stevan Little .IP "\(bu" 4 Dave Rolsky .IP "\(bu" 4 Jesse Luehrs .IP "\(bu" 4 Shawn M Moore .IP "\(bu" 4 \&\s-1XXXX XXX\s0'\s-1XX \s0(Yuval Kogman) .IP "\(bu" 4 Karen Etheridge .IP "\(bu" 4 Florian Ragwitz .IP "\(bu" 4 Hans Dieter Pearcey .IP "\(bu" 4 Chris Prather .IP "\(bu" 4 Matt S Trout .SH "COPYRIGHT AND LICENSE" .IX Header "COPYRIGHT AND LICENSE" This software is copyright (c) 2006 by Infinity Interactive, Inc.. .PP This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.