fn abc() ?[]int {
    return [1, 2, 3]
}

fn arr_opt(arr ?[]string) ? {
    assert arr != none
    assert arr?.len != 0

    for k, v in arr {
        assert arr?[k] == 'foo'
        assert v == 'foo'
    }
}

fn test_main() {
    mut var2 := abc()?
    assert var2.len == 3

    mut var := ?[]int{}
    assert var == none
    if var == none {
        var = [1]
    }
    assert var != none
    assert var?[0] == 1
    assert var?.len == 1

    mut var3 := ?[]string{}
    assert var3 == none
    var3 = ['foo']
    assert var3 != none

    arr_opt(var3)
    arr_opt([]string{len: 4, init: 'foo'})
    arr_opt(['foo', 'foo', 'foo', 'foo'])
}