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|
=pod
=head1 NAME
Moose::Cookbook::Basics::Recipe6 - The augment/inner example
=head1 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;
=head1 DESCRIPTION
This recipe shows how the C<augment> method modifier works. This
modifier reverses the normal subclass to parent method resolution
order. With an C<augment> modifier the I<least> specific method is
called first. Each successive call to C<inner> descends the
inheritance tree, ending at the most specific subclass.
The C<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 C<TPSReport> class.
We start with the least specific class, C<Document::Page>. Its create
method contains a call to C<inner()>:
sub create {
my $self = shift;
$self->open_page;
inner();
$self->close_page;
}
The C<inner> function is exported by C<Moose>, and is like C<super>
for augmented methods. When C<inner> is called, Moose finds the next
method in the chain, which is the C<augment> modifier in
C<Document::PageWithHeadersAndFooters>. You'll note that we can call
C<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 C<TPSReport> class.
Finally, in the C<TPSReport> class, the chain comes to an end:
augment 'create' => sub {
my $self = shift;
$self->create_tps_report;
inner();
};
We do call the C<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 C<TPSReport> in the future.
=head1 CONCLUSION
The C<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.
=head1 AUTHOR
Stevan Little E<lt>stevan@iinteractive.comE<gt>
Dave Rolsky E<lt>autarch@urth.orgE<gt>
=head1 COPYRIGHT AND LICENSE
Copyright 2007-2009 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.
=begin testing
my $tps_report = TPSReport->new;
isa_ok( $tps_report, 'TPSReport' );
is(
$tps_report->create,
q{<page><header/><report type="tps"/><footer/></page>},
'... got the right TPS report'
);
=end testing
=cut
|
