Controlling the build

• BUILD is called after new creates the object but before it is returned to the caller

package Class;
use Moose;
...

sub BUILD {
    my $self = shift;
    $self->do_stuff;
    return; # return value is ignored
}

• Checking complex constraints

sub BUILD {
    my $self = shift;

    confess 'if foo is 42, then bar should be less than 8'
       unless $self->foo == 42 && $self->bar < 8;

    $self->bar(64) if $self->quux->is_bazzy;
}

• DEMOLISH is like destroy