Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages

  
 
  

home | help
Moose::Cookbook::BasMoUser:Contribu:edaPerl:DocumentationuilderAndLazyBuild(3)

NAME
       Moose::Cookbook::Basics::BinaryTree_BuilderAndLazyBuild - Builder
       methods and lazy_build

VERSION
       version 2.2005

SYNOPSIS
	 package BinaryTree;
	 use Moose;

	 has 'node' => (is => 'rw', isa	=> 'Any');

	 has 'parent' => (
	     is	       => 'rw',
	     isa       => 'BinaryTree',
	     predicate => 'has_parent',
	     weak_ref  => 1,
	 );

	 has 'left' => (
	     is	       => 'rw',
	     isa       => 'BinaryTree',
	     predicate => 'has_left',
	     lazy      => 1,
	     builder   => '_build_child_tree',
	 );

	 has 'right' =>	(
	     is	       => 'rw',
	     isa       => 'BinaryTree',
	     predicate => 'has_right',
	     lazy      => 1,
	     builder   => '_build_child_tree',
	 );

	 before	'right', 'left'	=> sub {
	     my	($self,	$tree) = @_;
	     $tree->parent($self) if defined $tree;
	 };

	 sub _build_child_tree {
	     my	$self =	shift;

	     return BinaryTree->new( parent => $self );
	 }

DESCRIPTION
       If you've already read
       Moose::Cookbook::Basics::BinaryTree_AttributeFeatures, then this
       example should look very	familiar. In fact, all we've done here is
       replace the attribute's "default" parameter with	a "builder".

       In this particular case,	the "default" and "builder" options act	in
       exactly the same	way. When the "left" or	"right"	attribute is read,
       Moose calls the builder method to initialize the	attribute.

       Note that Moose calls the builder method	on the object which has	the
       attribute. Here's an example:

	 my $tree = BinaryTree->new();

	 my $left = $tree->left();

       When "$tree->left()" is called, Moose calls
       "$tree->_build_child_tree()" in order to	populate the "left" attribute.
       If we had passed	"left" to the original constructor, the	builder	would
       not be called.

       There are some differences between "default" and	"builder". Notably, a
       builder is subclassable,	and can	be composed from a role. See
       Moose::Manual::Attributes for more details.

   The lazy_build shortcut
       The "lazy_build"	attribute option can be	used as	sugar to specify a
       whole set of attribute options at once:

	 has 'animal' => (
	     is		=> 'ro',
	     isa	=> 'Animal',
	     lazy_build	=> 1,
	 );

       This is a shorthand for:

	 has 'animal' => (
	     is	       => 'ro',
	     isa       => 'Animal',
	     required  => 1,
	     lazy      => 1,
	     builder   => '_build_animal',
	     predicate => 'has_animal',
	     clearer   => 'clear_animal',
	 );

       If your attribute starts	with an	underscore, Moose is smart and will do
       the right thing with the	"predicate" and	"clearer", making them both
       start with an underscore. The "builder" method always starts with an
       underscore.

       You can read more about "lazy_build" in Moose::Meta::Attribute

CONCLUSION
       The "builder" option is a more OO-friendly version of the "default"
       functionality. It also separates	the default-generating code into a
       well-defined method. Sprinkling your attribute definitions with
       anonymous subroutines can be quite ugly and hard	to follow.

AUTHORS
       o   Stevan Little <stevan.little@iinteractive.com>

       o   Dave	Rolsky <autarch@urth.org>

       o   Jesse Luehrs	<doy@tozt.net>

       o   Shawn M Moore <code@sartak.org>

       o   xxxx	x<section>xx'xx	(Yuval Kogman) <nothingmuch@woobling.org>

       o   Karen Etheridge <ether@cpan.org>

       o   Florian Ragwitz <rafl@debian.org>

       o   Hans	Dieter Pearcey <hdp@weftsoar.net>

       o   Chris Prather <chris@prather.org>

       o   Matt	S Trout	<mst@shadowcat.co.uk>

COPYRIGHT AND LICENSE
       This software is	copyright (c) 2006 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 v5.24.1	    Moose::Cookbook::Basics::BinaryTree_BuilderAndLazyBuild(3)

NAME | VERSION | SYNOPSIS | DESCRIPTION | CONCLUSION | AUTHORS | COPYRIGHT AND LICENSE

Want to link to this manual page? Use this URL:
<https://www.freebsd.org/cgi/man.cgi?query=Moose::Cookbook::Basics::BinaryTree_BuilderAndLazyBuild&sektion=3&manpath=FreeBSD+12.0-RELEASE+and+Ports>

home | help