Name

Mo::default - Adds the default feature to Mo's has

Synopsis

use Mo qw'default';
has job  => ( default => 'Killer' );
has name => ( default => sub { 'Joe' } );
has age      => 42;
has colors   => [ 'green', 'blue' ];

Description

Adds the default parameter to has, which expects a value. If the value is a code ref, it is called to produce the default. If the value is a hash or array ref, then a shallow copy is made for the default. If there is an odd number of arguments after the attribute name, then the first value is the default.

These 3 lines are the same:

has things => default => sub {+{}};
has things => default => {};
has things => {};

Laziness

Default attribute values in Mo are lazy by default. This can be changed by explicitly setting the lazy argument to false, in order to cause it to be initialized during instantiation.

use Mo qw'default';
has status   => 'active';                 # lazy
has location => sub { ... }, lazy => 1;   # lazy
has target   => sub { ... }, lazy => 0;   # eager

To change the default behavior and make attributes to be initialized eagerly by default, import nonlazy.

use Mo qw'default nonlazy';
has status   => 'active';                 # eager
has location => sub { ... }, lazy => 1;   # lazy
has target   => sub { ... }, lazy => 0;   # eager