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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\*(Aq) }
\& sub close_page { (shift)\->append_body(\*(Aq\*(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\*(Aq) }
\& sub create_footer { (shift)\->append_body(\*(Aq\*(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\*(Aq);
\& }
\&
\& #
\& 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
.IP "\(bu" 4
Dave Rolsky
.IP "\(bu" 4
Jesse Luehrs
.IP "\(bu" 4
Shawn M Moore
.IP "\(bu" 4
יובל קוג'מן (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.