subset Longitude of Rat where -180 <= * <= 180; subset Latitude of Rat where -90 <= * <= 90; class GeoPoint { has Latitude $.lat is rw = 0; has Longitude $.lon is rw = 0; method gist { ($!lat >= 0 ?? "N$!lat" !! "S{-$!lat}") ~ " " ~ ($!lon >= 0 ?? "E$!lon" !! "W{-$!lon}") } } my $geo = GeoPoint.new(lat => 39.1915045); $geo.lon = "Tuesday"; # Type Check Error!