module main

interface TestInterface {
    test_func() f64
}

struct Struct1 {
    num f64
}

fn (o &Struct1) test_func() f64 {
    return o.num
}

struct Struct2 {
mut:
    s1 ?&Struct1
}

fn do_thing[T](s1 Struct1) T {
    mut t := T{}
    t.s1 = &s1
    $for field in T.fields {
        $if field.typ is TestInterface {
            i := TestInterface(t.$(field.name))
            assert false
        } $else $if field.typ is ?TestInterface {
            i := TestInterface(t.$(field.name) ?)
            assert true
        }
    }
    return t
}

fn test_main() {
    assert do_thing[Struct2](Struct1{1.23}).s1?.num == 1.23
}