# this is like the cross ref example in class-decls, but the return types are nilable
class Test

	def main
		is shared
		assert Letter.fromNumber(Number(1)).value=='a'
		assert Number.fromLetter(Letter('b')).value==2

class Letter

	var _value as String
	
	cue init(value as String)
		base.init
		_value = value
		
	get value from _value

	def fromNumber(n as Number) as Letter?
		is shared
		branch n.value
			on 1, return Letter('a')
			on 2, return Letter('b')
		return nil

class Number

	var _value as int

	cue init(value as int)
		base.init
		_value = value
		
	get value from _value
	
	def fromLetter(le as Letter) as Number?
		is shared
		branch le.value
			on 'a', return Number(1)
			on 'b', return Number(2)
		return nil