[Perl]Mooseでコンストラクタの挙動を変える

BUILDメソッドを定義することで対応できる。

package MyCar;
use Data::Dumper;
use Moose;

has 'speed' => ( is => 'rw', isa => 'Int' );

sub BUILD {
    my $self = shift;
    $self->speed( 50 ) if !$self->speed;
}

no Moose;

my $super_car = MyCar->new( speed => 200 );
my $normal_car = MyCar->new;

print "=== Super Car ===\n". Dumper $super_car;
print "=== Normal Car ===\n". Dumper $normal_car;

結果

=== Super Car ===
$VAR1 = bless( {
                 'speed' => 200
               }, 'MyCar' );
=== Normal Car ===
$VAR1 = bless( {
                 'speed' => 50
               }, 'MyCar' );