Flon's Law at work.

Main.hx

class A {
	public var i(get, null):Int;
	public function new() i = 0
	function get_i() return i--
}
class Main {
	static function main() 
		switch (new A()) {
			case a if (a.i < 0): trace('negative');
			case a if (a.i == 0): trace('zero');
			case a if (a.i > 0): trace('positive');
			default: trace('without sign')
		}		
}