Support traits that can't implement erased_serde::Serialize directly #113
Description
I have types that erased_serde::Serialize directly because they require extra arguments for context, so instead they have a custom serialize method. Unfortunately, this prevents me from using erased_serde::serialize, because the erased_serde::Serialize is sealed. Here's what I would like to work:
trait Object {
fn erased_serialize(
&self,
extra: &str,
serializer: &dyn erased_serde::Serializer,
) -> Result<(), erased_serde::Error>;
// fn do_erased_serialize...
}
struct Manager {
extra: String,
object: Box<dyn Object>,
}
impl serde::Serialize for Manager {
fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
where
S: serde::Serializer,
{
struct SerializeObjectWithExtra<'a>(&'a dyn Object, &'a str);
// This part is not supported currently.
impl erased_serde::SerializeBecause for SerializeObjectWithExtra<'_> {
fn erased_serialize(
&self,
serializer: &mut dyn erased_serde::Serializer,
) -> Result<(), erased_serde::Error> {
self.0.serialize(self.1, serializer)
}
// fn do_erased_serialize...
}
erased_serde::serialize(
&SerializeObjectWithExtra(&*self.object, &self.extra),
serializer,
)
}
}The way I am hacking around this currently is instead defining Object as:
trait Object {
fn as_serialize<'a>(&'a self, extra: &'a str) -> Box<dyn erased_serde::Serialize + 'a>;
}But this requires an extra allocation that I would like to avoid.
I'm not sure if unsealing erased_serde::Serialize is the best way to support this, because as I understand it, erased_serde needs access to a concrete serde::Serialize at some point to create the erased type, and you probably don't want to expose do_erased_serialize publicly. Is there a better way to do this?