.\" Automatically generated by Pod::Man 2.28 (Pod::Simple 3.28) .\" .\" 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 .. .\" Set up some character translations and predefined strings. \*(-- will .\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left .\" double quote, and \*(R" will give a right double quote. \*(C+ will .\" give a nicer C++. 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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 2.1213 .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 \&\s-1XXXX XXX\s0'\s-1XX \s0(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.