Editing Constructor (object-oriented programming) (section)

==== Perl 5 with Moose ====
In the [[Moose perl|Moose object system]] for Perl, most of this boilerplate can be omitted, a default ''new'' is created, attributes can be specified, and whether they can be set, reset, or are required. In addition, any extra constructor functionality can be included in a ''BUILD'' method which the Moose generated constructor will call, after it has checked the arguments.  A ''BUILDARGS'' method can be specified to handle constructor arguments not in hashref / key => value form.

<syntaxhighlight lang="perl">
package Person;
# enable Moose-style object construction
use Moose;

# first name ( a string) can only be set at construction time ('ro')
has first_name => (is => 'ro', isa => 'Str', required => 1);
# last name ( a string) can only be set at construction time ('ro')
has last_name  => (is => 'ro', isa => 'Str', required => 1);
# age (Integer) can be modified after construction ('rw'), and is not required
# to be passed to be constructor.  Also creates a 'has_age' method which returns
# true if age has been set
has age        => (is => 'rw', isa => 'Int', predicate => 'has_age');

# Check custom requirements
sub BUILD {
      my $self = shift;
      if ($self->has_age && $self->age < 18) { # no under 18s
           die "No under-18 Persons";
      }
}
1;
</syntaxhighlight>

In both cases the Person class is instiated like this:
<syntaxhighlight lang="perl">
use Person;
my $p = Person->new( first_name => 'Sam', last_name => 'Ashe', age => 42 );
</syntaxhighlight>