struct IntArray {
    a []int
}

fn encode_array[U](val []U) []string {
    mut out := []string{}
    $if U is int {
        out << 'is int'
    } $else $if U is $struct {
        out << 'is struct'
    }
    return out
}

fn encode_struct[U](val U) ?[]string {
    $for field in U.fields {
        if field.is_array {
            value := val.$(field.name)
            return encode_array(value)
        }
    }
    return none
}

fn test_main() {
    int_array := IntArray{
        a: [1, 2, 3]
    }
    assert encode_struct(int_array)?.str() == "['is int']"
}