struct Bar {
mut:
    a int
}

struct Foo {
    field ?&Bar
}

fn t(mut opt ?Bar) {
    v := Foo{
        field: opt
    }
    if opt == none {
        assert opt == none
        assert v.field == none
    } else {
        assert opt.a == 123
        assert v.field != none
    }
    if mut opt != none {
        opt.a = 321
    }
}

fn test_main() {
    mut var := ?&Bar(none)
    t(mut var)
    assert var == none
}

fn test_not_none() {
    mut var := ?&Bar(&Bar{
        a: 123
    })
    t(mut var)
    assert var != none
    assert var?.a == 321
}