struct FixedStruct1 {
    a int
    b string
    c ?int
    d ?string
}

struct Encoder {}

fn test_main() {
    fixed := FixedStruct1{123, '456', 789, '321'}
    // this work well
    println(fixed.a.str())
    println(fixed.c?.str())

    println(fixed.b.int())
    println(fixed.d?.int())

    e := Encoder{}
    // this not work
    e.encode_struct(fixed)
}

fn (e &Encoder) encode_struct[T](val T) {
    mut count := 0
    $for field in T.fields {
        mut value := val.$(field.name)
        $if field.is_option {
            if field.name in ['c', 'd'] {
                assert true
            }
            println('>> ${value ?.str()}')
            println(val.$(field.name) ?.str())
            count += 1
        }
    }
    assert count == 2
}