NAME<\/a> Moose::Cookbook::Basics::BinaryTree_BuilderAndLazyBuild \u2212 Builder methods and lazy_build<\/p>\n version 2.2014<\/p>\n package BinaryTree; If you\u2019ve already read Moose::Cookbook::Basics::BinaryTree_AttributeFeatures, then this example should look very familiar. In fact, all we\u2019ve done here is replace the attribute\u2019s “default” parameter with a “builder”.<\/p>\n 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.<\/p>\n Note that Moose calls the builder method on the object which has the attribute<\/i>. Here\u2019s an example:<\/p>\n my $tree = BinaryTree\u2212>new(); When “$tree\u2212>left()” is called, Moose calls “$tree\u2212>_build_child_tree()” in order to populate the “left” attribute. If we had passed “left” to the original constructor, the builder would not be called.<\/p>\n There are some differences between “default” and “builder”. Notably, a builder is subclassable, and can be composed from a role. See Moose::Manual::Attributes for more details.<\/p>\n The lazy_build shortcut<\/b> has ‘animal’ => ( This is a shorthand for:<\/p>\n has ‘animal’ => ( If your attribute starts with an underscore, Moose is smart and will do the right thing with the “predicate” and “clearer”, making them both start with an underscore. The “builder” method always<\/i> starts with an underscore.<\/p>\n You can read more about “lazy_build” in Moose::Meta::Attribute<\/p>\n The “builder” option is a more OO-friendly version of the “default” functionality. It also separates the default-generating code into a well-defined method. Sprinkling your attribute definitions with anonymous subroutines can be quite ugly and hard to follow.<\/p>\n
VERSION<\/a>
SYNOPSIS<\/a>
DESCRIPTION<\/a>
CONCLUSION<\/a>
AUTHORS<\/a>
COPYRIGHT AND LICENSE<\/a> <\/p>\n
\nNAME <\/a> <\/h2>\n
VERSION <\/a> <\/h2>\n
SYNOPSIS <\/a> <\/h2>\n
use Moose;
has ‘node’ => (is => ‘rw’, isa => ‘Any’);
has ‘parent’ => (
is => ‘rw’,
isa => ‘BinaryTree’,
predicate => ‘has_parent’,
weak_ref => 1,
);
has ‘left’ => (
is => ‘rw’,
isa => ‘BinaryTree’,
predicate => ‘has_left’,
lazy => 1,
builder => ‘_build_child_tree’,
);
has ‘right’ => (
is => ‘rw’,
isa => ‘BinaryTree’,
predicate => ‘has_right’,
lazy => 1,
builder => ‘_build_child_tree’,
);
before ‘right’, ‘left’ => sub {
my ($self, $tree) = @_;
$tree\u2212>parent($self) if defined $tree;
};
sub _build_child_tree {
my $self = shift;
return BinaryTree\u2212>new( parent => $self );
}<\/p>\nDESCRIPTION <\/a> <\/h2>\n
my $left = $tree\u2212>left();<\/p>\n
The “lazy_build” attribute option can be used as sugar to specify a whole set of attribute options at once:<\/p>\n
is => ‘ro’,
isa => ‘Animal’,
lazy_build => 1,
);<\/p>\n
is => ‘ro’,
isa => ‘Animal’,
required => 1,
lazy => 1,
builder => ‘_build_animal’,
predicate => ‘has_animal’,
clearer => ‘clear_animal’,
);<\/p>\nCONCLUSION <\/a> <\/h2>\n
AUTHORS <\/a> <\/h2>\n
| <\/td>\n | \n \u2022<\/p>\n<\/td>\n | <\/td>\n | \n Stevan Little \u2022<\/p>\n<\/td>\n Dave Rolsky \u2022<\/p>\n<\/td>\n Jesse Luehrs \u2022<\/p>\n<\/td>\n Shawn M Moore \u2022<\/p>\n<\/td>\n \u00d7\u00d7\u00d7\u00d7 \u00d7\u00a7\u00d7\u00d7\u2019\u00d7\u00d7 (Yuval Kogman) \u2022<\/p>\n<\/td>\n Karen Etheridge \u2022<\/p>\n<\/td>\n Florian Ragwitz \u2022<\/p>\n<\/td>\n Hans Dieter Pearcey \u2022<\/p>\n<\/td>\n |