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.IX Title "Moose::Cookbook::Basics::Document_AugmentAndInner 3pm"
.TH Moose::Cookbook::Basics::Document_AugmentAndInner 3pm "2023-01-30" "perl v5.36.0" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
Moose::Cookbook::Basics::Document_AugmentAndInner \- The augment modifier, which turns normal method overriding "inside\-out"
.SH "VERSION"
.IX Header "VERSION"
version 2.2203
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 2
\&  package Document::Page;
\&  use Moose;
\&
\&  has \*(Aqbody\*(Aq => ( is => \*(Aqrw\*(Aq, isa => \*(AqStr\*(Aq, default => sub {\*(Aq\*(Aq} );
\&
\&  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(\*(Aq<page>\*(Aq) }
\&  sub close_page { (shift)\->append_body(\*(Aq</page>\*(Aq) }
\&
\&  package Document::PageWithHeadersAndFooters;
\&  use Moose;
\&
\&  extends \*(AqDocument::Page\*(Aq;
\&
\&  augment \*(Aqcreate\*(Aq => sub {
\&      my $self = shift;
\&      $self\->create_header;
\&      inner();
\&      $self\->create_footer;
\&  };
\&
\&  sub create_header { (shift)\->append_body(\*(Aq<header/>\*(Aq) }
\&  sub create_footer { (shift)\->append_body(\*(Aq<footer/>\*(Aq) }
\&
\&  package TPSReport;
\&  use Moose;
\&
\&  extends \*(AqDocument::PageWithHeadersAndFooters\*(Aq;
\&
\&  augment \*(Aqcreate\*(Aq => sub {
\&      my $self = shift;
\&      $self\->create_tps_report;
\&      inner();
\&  };
\&
\&  sub create_tps_report {
\&      (shift)\->append_body(\*(Aq<report type="tps"/>\*(Aq);
\&  }
\&
\&  # <page><header/><report type="tps"/><footer/></page>
\&  my $report_xml = TPSReport\->new\->create;
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
This recipe shows how the \f(CW\*(C`augment\*(C'\fR method modifier works. This
modifier reverses the normal subclass to parent method resolution
order. With an \f(CW\*(C`augment\*(C'\fR modifier the \fIleast\fR specific method is
called first. Each successive call to \f(CW\*(C`inner\*(C'\fR descends the
inheritance tree, ending at the most specific subclass.
.PP
The \f(CW\*(C`augment\*(C'\fR 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.
.PP
In the example above, we've created a set of document classes, with
the most specific being the \f(CW\*(C`TPSReport\*(C'\fR class.
.PP
We start with the least specific class, \f(CW\*(C`Document::Page\*(C'\fR. Its create
method contains a call to \f(CW\*(C`inner()\*(C'\fR:
.PP
.Vb 6
\&  sub create {
\&      my $self = shift;
\&      $self\->open_page;
\&      inner();
\&      $self\->close_page;
\&  }
.Ve
.PP
The \f(CW\*(C`inner\*(C'\fR function is exported by \f(CW\*(C`Moose\*(C'\fR, and is like \f(CW\*(C`super\*(C'\fR
for augmented methods. When \f(CW\*(C`inner\*(C'\fR is called, Moose finds the next
method in the chain, which is the \f(CW\*(C`augment\*(C'\fR modifier in
\&\f(CW\*(C`Document::PageWithHeadersAndFooters\*(C'\fR. You'll note that we can call
\&\f(CW\*(C`inner\*(C'\fR in our modifier:
.PP
.Vb 6
\&  augment \*(Aqcreate\*(Aq => sub {
\&      my $self = shift;
\&      $self\->create_header;
\&      inner();
\&      $self\->create_footer;
\&  };
.Ve
.PP
This finds the next most specific modifier, in the \f(CW\*(C`TPSReport\*(C'\fR class.
.PP
Finally, in the \f(CW\*(C`TPSReport\*(C'\fR class, the chain comes to an end:
.PP
.Vb 5
\&  augment \*(Aqcreate\*(Aq => sub {
\&      my $self = shift;
\&      $self\->create_tps_report;
\&      inner();
\&  };
.Ve
.PP
We do call the \f(CW\*(C`inner\*(C'\fR 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 \f(CW\*(C`TPSReport\*(C'\fR in the future.
.SH "CONCLUSION"
.IX Header "CONCLUSION"
The \f(CW\*(C`augment\*(C'\fR 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.
.SH "AUTHORS"
.IX Header "AUTHORS"
.IP "\(bu" 4
Stevan Little <stevan@cpan.org>
.IP "\(bu" 4
Dave Rolsky <autarch@urth.org>
.IP "\(bu" 4
Jesse Luehrs <doy@cpan.org>
.IP "\(bu" 4
Shawn M Moore <sartak@cpan.org>
.IP "\(bu" 4
יובל קוג'מן (Yuval Kogman) <nothingmuch@woobling.org>
.IP "\(bu" 4
Karen Etheridge <ether@cpan.org>
.IP "\(bu" 4
Florian Ragwitz <rafl@debian.org>
.IP "\(bu" 4
Hans Dieter Pearcey <hdp@cpan.org>
.IP "\(bu" 4
Chris Prather <chris@prather.org>
.IP "\(bu" 4
Matt S Trout <mstrout@cpan.org>
.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.