class Test

	def main is shared
		Test().run
	
	def run
		# to ? and to ! on a reference type (String)
		s = 'aoeu' to ?
		assert s
		s = nil  # must work because s is String?
		assert s is nil
		s = 'aoeu'
		
		t = s to !
		.foo(t)  # foo only takes String, not String?
	
		# to ? and to ! on a value type (DateTime)
		d = DateTime.now to ?
		d = nil  # must work because d is DateTime?
		assert d is nil
		d = DateTime.now
		
		e = d to !
		.bar(e) # bar only takes DateTime, not DateTime?
		
	def foo(s as String)
		assert s.length

	def bar(dt as DateTime)
		assert dt.year > 2000