struct Foo {
mut:
    name string
}

struct Test {
pub mut:
    a string
    b ?string
}

fn (mut f Foo) test(arr ?[]int) ?string {
    return arr?.len.str()
}

fn (mut f Foo) test2() ?string {
    return none
}

fn fn_a(s ?Test) ? {
    println(s?.a)
    assert false
}

fn fn_b(s ?Test) ? {
    println(s?.b?)
    assert false
}

fn test_main() {
    mut m := ?Foo{}
    assert m == none
    m = Foo{
        name: 'foo'
    }
    assert m != none
    v := m?.test([1, 2, 3]) or { '4' }
    m?.name = 'foo'
    assert m?.name == 'foo'
    assert v == '3'
    var := m?.test2() or { '' }
    assert var == ''
}

fn test_opt_call() {
    mut t := ?Test{}
    fn_a(none) // returns none
    fn_b(t) // returns none
}