Страницы справочника OS X

Эта страница руководства для  версии 10.9 Mac OS X

Читать страницы руководства

Moose::Cookbook::Basics::Recipe6(3)  User Contributed Perl Documentation Moose::Cookbook::Basics::Recipe6(3)



NAME
       Moose::Cookbook::Basics::Recipe6 - The augment/inner example

VERSION
       version 2.0205

SYNOPSIS
         package Document::Page;
         use Moose;

         has 'body' => ( is => 'rw', isa => 'Str', default => sub {''} );

         sub create {
             my $self = shift;
             $self->open_page;
             inner();
             $self->close_page;
         }

         sub append_body {
             my ( $self, $appendage ) = @_;
             $self->body( $self->body . $appendage );
         }

         sub open_page  { (shift)->append_body('<page>') }
         sub close_page { (shift)->append_body('</page>') }

         package Document::PageWithHeadersAndFooters;
         use Moose;

         extends 'Document::Page';

         augment 'create' => sub {
             my $self = shift;
             $self->create_header;
             inner();
             $self->create_footer;
         };

         sub create_header { (shift)->append_body('<header/>') }
         sub create_footer { (shift)->append_body('<footer/>') }

         package TPSReport;
         use Moose;

         extends 'Document::PageWithHeadersAndFooters';

         augment 'create' => sub {
             my $self = shift;
             $self->create_tps_report;
             inner();
         };

         sub create_tps_report {
             (shift)->append_body('<report type="tps"/>');
         }

         # <page><header/><report type="tps"/><footer/></page>
         my $report_xml = TPSReport->new->create;

DESCRIPTION
       This recipe shows how the "augment" method modifier works. This modifier reverses the normal subclass
       to parent method resolution order. With an "augment" modifier the least specific method is called
       first. Each successive call to "inner" descends the inheritance tree, ending at the most specific
       subclass.

       The "augment" modifier lets you design a parent class that can be extended in a specific way. The
       parent provides generic wrapper functionality, and the subclasses fill in the details.

       In the example above, we've created a set of document classes, with the most specific being the
       "TPSReport" class.

       We start with the least specific class, "Document::Page". Its create method contains a call to
       "inner()":

         sub create {
             my $self = shift;
             $self->open_page;
             inner();
             $self->close_page;
         }

       The "inner" function is exported by "Moose", and is like "super" for augmented methods. When "inner"
       is called, Moose finds the next method in the chain, which is the "augment" modifier in
       "Document::PageWithHeadersAndFooters". You'll note that we can call "inner" in our modifier:

         augment 'create' => sub {
             my $self = shift;
             $self->create_header;
             inner();
             $self->create_footer;
         };

       This finds the next most specific modifier, in the "TPSReport" class.

       Finally, in the "TPSReport" class, the chain comes to an end:

         augment 'create' => sub {
             my $self = shift;
             $self->create_tps_report;
             inner();
         };

       We do call the "inner" function one more time, but since there is no more specific subclass, this is
       a no-op. Making this call means we can easily subclass "TPSReport" in the future.

CONCLUSION
       The "augment" modifier is a powerful tool for creating a set of nested wrappers. It's not something
       you will need often, but when you do, it is very handy.

AUTHOR
       Stevan Little <stevan@iinteractive.com>

COPYRIGHT AND LICENSE
       This software is copyright (c) 2011 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 v5.12.5                                     2011-09-06              Moose::Cookbook::Basics::Recipe6(3)