During serialization, internally tagged enums invoke the Serializer's
serialize_struct. In JSON this turns into a map which uses visit_map
when deserialized. But some formats employ visit_seq when
deserializing a struct. One example is rmp-serde. Such formats were
previously unable to deserialize an internally tagged enum. This
change fixes it by adding visit_seq for internally tagged enums.
Since we know exactly how many bytes we should serialize as we can hint
to the serializer that it is not required which further reduces the
serialized size when compared to just serializing as bytes.
This implements the KISS suggested in https://github.com/serde-rs/serde/issues/790.
It is possible that one of the other approaches may be better but this
seemed like the simplest one to reignite som discussion.
Personally I find the original suggestion of adding two traits perhaps slightly
cleaner in theory but I think it ends up more complicated in the end
since the added traits also need to be duplicated to to the `Seed`
traits.
Closes#790
This adds two new types to the `de::value` module,
`BorrowedStrDeserializer` and `BorrowedBytesDeserializer`. A
`BorrowedStrDeserializer` is just like `StrDeserializer`, except the
lifetime of the string is tied to the lifetime of the deserializer. This
can be useful when, for example, deserializing into a
`HashMap<&str, &str>` when the keys/values are tied to the deserializer
itself.
The `BorrowedBytesDeserializer` has no analog, but it's the same as
`BorrowedStrDeserialize` except for `&[u8]` instead of `&str`.
David Tolnay