Instance (keyed data types) support

[willstott101]

I notice there are no references to register_instance in this library. Are instances (and instance handles) supported by this wrapper currently? Specifically "deleting" a sample from the DDS data space (dispose_instance_handle).

I notice in dds_derive we have:

fn is_key(field : &Field) -> bool {
    for attr in &field.attrs {
        if let Some(ident) = attr.path.get_ident() {
            if ident == "topic_key" || ident == "topic_key_enum"{
                return true
            }
        } 
    }
    false
}

implying that they might be supported for well-known field names only. If that's the case, is there any way to customize serialized field names? Which is relevant for hashed autoid field names

[sjames]

Hi @willstott101,
Instances are only supported for known field names. The the key-hash is generated according to how CDDS expects it when a type has keys.

Reader instances are not supported. I still have to figure out how to support this while using the custom topic API that CDDS exposes. (see https://github.com/sjames/cyclonedds-rs/blob/master/src/serdes.rs)

I would love to hear your thoughts on how the user API could look like.