Casting between ArcOSMObj and StringOSMObj?

[erictapen]

Thanks for this great piece of software.

I'm currently struggling with converting StringOSMObj to an ArcOSMObj. My intuition is that it shouldn't be a problem, as I already was able to stream objects from an PBFReader to an XMLWriter. And of course there is the OSMObj trait.

My problem boils down to this: I want to write a test for a function show_id that in production only processes ArcOSMObj from an PBFReader. However for the test I'd like to be able to write xml, as it is more convenient. I have no problem with putting the trait OSMObj into show_id's type signature instead of ArcOSMObj.

However this doesn't compile:

use osmio::{OSMObj, ObjId};

fn show_id(obj: dyn OSMObj) -> ObjId {
    obj.id()
}

fn main() {
    println!("Hello, world!");
}

#[cfg(test)]
mod tests {
    use super::*;
    use osmio::xml::XMLReader;
    use osmio::OSMReader;

    #[test]
    fn test_show_version() {
        let xml = r#"
          <?xml version="1.0" encoding="utf-8"?>
          <osm version="0.6">
            <node id="1" lat="0.0" lon="0.0"/>
          </osm>
        "#;
        let reader = XMLReader::new(xml.as_bytes());
        for obj in reader.objects() {
            assert_eq!(1, show_id(obj));
        }
    }
}

$ rustc --version
rustc 1.55.0

$ cargo test
   Compiling cast_test v0.1.0 (/home/kerstin/fh/cityvis/camps/osm-history/cast_test)
error[E0038]: the trait `OSMObj` cannot be made into an object
   --> src/main.rs:3:17
    |
3   | fn show_id(obj: dyn OSMObj) -> ObjId {
    |                 ^^^^^^^^^^ `OSMObj` cannot be made into an object
    |
note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
   --> /home/kerstin/.cargo/registry/src/github.com-1ecc6299db9ec823/osmio-0.6.0/src/lib.rs:285:23
    |
285 | pub trait OSMObjBase: PartialEq + Debug + Clone {
    |                       ^^^^^^^^^ the trait cannot be made into an object because it uses `Self` as a type parameter

For more information about this error, try `rustc --explain E0038`.
error: could not compile `cast_test` due to previous error

Any ideas on how to achieve this?

[erictapen]

Nevermind, figured that my problem was something entirely different. The test case above was solved with

//              v
fn show_id(obj: impl OSMObj) -> ObjId {
    obj.id()
}