#- virtual attributes -#

def assert_attribute_error(f)
    try
        f()
        assert(false, 'unexpected execution flow')
    except .. as e, m
        assert(e == 'attribute_error')
    end
end

class Ta
    var a, b, virtual_c
    def init()
        self.a = 1
        self.b = 2
        self.virtual_c = 3
    end
    def member(n)
        if n == 'c' return self.virtual_c end
        return nil
    end
    def setmember(n, v)
        if n == 'c' self.virtual_c = v return true end
        return false
    end
end
ta = Ta()

assert(ta.a == 1)
assert(ta.b == 2)
assert(ta.c == 3)
ta.a = 10
assert(ta.a == 10)
assert(ta.c == 3)
ta.c = 30
assert(ta.c == 30)
assert(ta.virtual_c == 30)
assert_attribute_error(def() ta.d = 0 end)