h2o -class=>'Point', -new, -meth, { angle => sub { my $self = shift; atan2($self->y, $self->x) }, }, qw/ x y /; my $one = Point->new(x=>1, y=>2); my $two = Point->new(x=>3, y=>4); $two->y(5); printf "%.4f\n", $two->angle; # prints 1.0304