serde: Unable to serialize sequence without knowing all elements.

In the logging library I’m working on, I would like to serialize map elements, provided by user API calls. However at any given time, I have only one key: value pair.

So I can’t efficiently serialize a map:

    fn serialize_map<V>(&mut self, visitor: V) -> Result<(), Self::Error> where V: MapVisitor;
    fn serialize_map_elt<K, V>(&mut self, key: K, value: V) -> Result<(), Self::Error> where K: Serialize, V: Serialize;

As I have to build a Visitor

If the API would be returning some kind of Visitor that one can call to serialize field after field, then both my and currently-supported use cases would work. Would it be worse in some aspect that I’m missing?