.\" -*- mode: troff; coding: utf-8 -*- .\" Automatically generated by Pod::Man 5.01 (Pod::Simple 3.43) .\" .\" Standard preamble: .\" ======================================================================== .de Sp \" Vertical space (when we can't use .PP) .if t .sp .5v .if n .sp .. .de Vb \" Begin verbatim text .ft CW .nf .ne \\$1 .. .de Ve \" End verbatim text .ft R .fi .. .\" \*(C` and \*(C' are quotes in nroff, nothing in troff, for use with C<>. .ie n \{\ . ds C` "" . ds C' "" 'br\} .el\{\ . ds C` . ds C' 'br\} .\" .\" Escape single quotes in literal strings from groff's Unicode transform. .ie \n(.g .ds Aq \(aq .el .ds Aq ' .\" .\" If the F register is >0, we'll generate index entries on stderr for .\" titles (.TH), headers (.SH), subsections (.SS), items (.Ip), and index .\" entries marked with X<> in POD. Of course, you'll have to process the .\" output yourself in some meaningful fashion. .\" .\" Avoid warning from groff about undefined register 'F'. .de IX .. .nr rF 0 .if \n(.g .if rF .nr rF 1 .if (\n(rF:(\n(.g==0)) \{\ . if \nF \{\ . de IX . tm Index:\\$1\t\\n%\t"\\$2" .. . if !\nF==2 \{\ . nr % 0 . nr F 2 . \} . \} .\} .rr rF .\" ======================================================================== .\" .IX Title "Moose::Cookbook::Basics::BinaryTree_BuilderAndLazyBuild 3pm" .TH Moose::Cookbook::Basics::BinaryTree_BuilderAndLazyBuild 3pm 2024-01-21 "perl v5.38.2" "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::BinaryTree_BuilderAndLazyBuild \- Builder methods and lazy_build .SH VERSION .IX Header "VERSION" version 2.2207 .SH SYNOPSIS .IX Header "SYNOPSIS" .Vb 2 \& package BinaryTree; \& use Moose; \& \& has \*(Aqnode\*(Aq => (is => \*(Aqrw\*(Aq, isa => \*(AqAny\*(Aq); \& \& has \*(Aqparent\*(Aq => ( \& is => \*(Aqrw\*(Aq, \& isa => \*(AqBinaryTree\*(Aq, \& predicate => \*(Aqhas_parent\*(Aq, \& weak_ref => 1, \& ); \& \& has \*(Aqleft\*(Aq => ( \& is => \*(Aqrw\*(Aq, \& isa => \*(AqBinaryTree\*(Aq, \& predicate => \*(Aqhas_left\*(Aq, \& lazy => 1, \& builder => \*(Aq_build_child_tree\*(Aq, \& ); \& \& has \*(Aqright\*(Aq => ( \& is => \*(Aqrw\*(Aq, \& isa => \*(AqBinaryTree\*(Aq, \& predicate => \*(Aqhas_right\*(Aq, \& lazy => 1, \& builder => \*(Aq_build_child_tree\*(Aq, \& ); \& \& before \*(Aqright\*(Aq, \*(Aqleft\*(Aq => sub { \& my ($self, $tree) = @_; \& $tree\->parent($self) if defined $tree; \& }; \& \& sub _build_child_tree { \& my $self = shift; \& \& return BinaryTree\->new( parent => $self ); \& } .Ve .SH DESCRIPTION .IX Header "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 \f(CW\*(C`default\*(C'\fR parameter with a \f(CW\*(C`builder\*(C'\fR. .PP In this particular case, the \f(CW\*(C`default\*(C'\fR and \f(CW\*(C`builder\*(C'\fR options act in exactly the same way. When the \f(CW\*(C`left\*(C'\fR or \f(CW\*(C`right\*(C'\fR attribute is read, Moose calls the builder method to initialize the attribute. .PP Note that Moose calls the builder method \fIon the object which has the attribute\fR. Here's an example: .PP .Vb 1 \& my $tree = BinaryTree\->new(); \& \& my $left = $tree\->left(); .Ve .PP When \f(CW\*(C`$tree\->left()\*(C'\fR is called, Moose calls \f(CW\*(C`$tree\->_build_child_tree()\*(C'\fR in order to populate the \f(CW\*(C`left\*(C'\fR attribute. If we had passed \f(CW\*(C`left\*(C'\fR to the original constructor, the builder would not be called. .PP There are some differences between \f(CW\*(C`default\*(C'\fR and \f(CW\*(C`builder\*(C'\fR. Notably, a builder is subclassable, and can be composed from a role. See Moose::Manual::Attributes for more details. .SS "The lazy_build shortcut" .IX Subsection "The lazy_build shortcut" The \f(CW\*(C`lazy_build\*(C'\fR attribute option can be used as sugar to specify a whole set of attribute options at once: .PP .Vb 5 \& has \*(Aqanimal\*(Aq => ( \& is => \*(Aqro\*(Aq, \& isa => \*(AqAnimal\*(Aq, \& lazy_build => 1, \& ); .Ve .PP This is a shorthand for: .PP .Vb 9 \& has \*(Aqanimal\*(Aq => ( \& is => \*(Aqro\*(Aq, \& isa => \*(AqAnimal\*(Aq, \& required => 1, \& lazy => 1, \& builder => \*(Aq_build_animal\*(Aq, \& predicate => \*(Aqhas_animal\*(Aq, \& clearer => \*(Aqclear_animal\*(Aq, \& ); .Ve .PP If your attribute starts with an underscore, Moose is smart and will do the right thing with the \f(CW\*(C`predicate\*(C'\fR and \f(CW\*(C`clearer\*(C'\fR, making them both start with an underscore. The \f(CW\*(C`builder\*(C'\fR method \fIalways\fR starts with an underscore. .PP You can read more about \f(CW\*(C`lazy_build\*(C'\fR in Moose::Meta::Attribute .SH CONCLUSION .IX Header "CONCLUSION" The \f(CW\*(C`builder\*(C'\fR option is a more OO-friendly version of the \f(CW\*(C`default\*(C'\fR 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. .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.