Am I passing metadata through DeserializeSeed to facilitate deserialization of algebraic datatypes as intended

[hirenhpatel]

Am I passing metadata through DeserializeSeed to facilitate deserialization of algebraic datatypes as intended

[dtolnay]

Usually you would implement DeserializeSeed on the same type that also has the corresponding Visitor impl. So a canonical impl would look like:

impl<'de> DeserializeSeed<'de> for TheVisitor {
    type Value = <Self as Visitor<'de>>::Value;

    fn deserialize<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
    where
        D: Deserializer<'de>,
    {
        deserializer.deserialize_………(self)
    }
}

[hirenhpatel]

The thought of implementing DeserializeSeed on Visitor never occurred to me! After studying your suggestion some more, I have settled on the pattern of having a surrogate nested visitor type DynamicVisitor<TupleVisitor<..., NodeVisitor<...>> that mirrors the target deserialization datatype: Dynamic<(..., NodeVisitor<...>)>.

I have implemented DeserializeSeed<'de> on all of the *Visitor structs, which have the metadata as needed. Then, most of the my deserialize calls look like this
deserializer.deserialize_*(self.0) to pass the inner visitor to the next step in the recursion.

Have I understand your guidance correctly?

Further, do I understand correctly that, in my recursive deserialization implementations, I should
not mix Deserialize with DeserializeSeed? That is, in any chain, I will be dealing with Deserialize<'de> exclusively, or with DeserializeSeed<'de> exclusively?

Thanks in advance