package Some::Class;

sub new : New {
    my ($self) = @_;
    exists $self->{$_} or croak "Mandatory argument '$_' missing"
        for qw(id foo);
    return $self;
}

sub id   : Property { /^\d+\z/ }
sub foo  : Property;
sub bar  : Property;
sub blah : Property { $_ < 50 }

sub _private : method {
    my ($self) = @_;
    ...
}

sub do_something : method {
    my ($self, $quux) = @_;
    ...
}

##</code><code>##

my $thing = Some::Class->new( id => 15, foo => "Hello" );
$thing->foo =~ s/e/a/;
$thing->id++;

$thing->do_something($$);

$thing->blah = 10;
$thing->blah = 60;  # dies